SPECTROMETER FOR ANALYSIS OF THE SPECTRUM OF A LIGHT BEAM

The invention relates to the field of optical metrology.

More particularly a spectrometer high diffraction efficiency for analysing the spectrum of a light or a light source regardless of the state of polarization of the light beam.

The invention is particularly advantageous when the spectrometer high efficiency over a wide spectral band is desired.

In optical metrology, the spectrometry is a technique that includes analyzing the spectrum of a light beam that upstream thereof is originating from a light source, or that it comes from an object illuminated by a light source to derive certain properties of the source or the object.

A spectrometer is an optical instrument for performing such analysis for a spectrum comprising a plurality of wavelengths.

It is well known to those skilled in the art as a spectrometer generally includes:

an entry slot adapted to pass a light beam upstream,

angular dispersion means adapted to angularly disperse an incident light beam as a function of a plurality of wavelengths,

In many applications, such as Raman spectroscopy or spectroscopy in the NIR range, the amount of light actually available at the output spectrometer, at detection means or of an output slit, for the analysis of the spectrum is low. A rapid measurement or accurate then be difficult.

Therefore, a spectrometer, whose means for angular dispersion have a very high efficiency over a wide spectral band, would be transported with a minimum loss the overall number of photons of the light beam upstream from the entry slot to the detection means or to the exit slot. This would provide greater rapidity and accuracy of measurement of the spectrometer for analyzing the spectrum of the upstream light beam.

Are known documents US2010/0225856A1 US2010/0225876A1 and angular dispersion means having at least one diffraction grating having polarization-splitting a very high diffraction efficiency in the diffraction orders +1 and -1 over a wide spectral range, particularly in the field of ultraviolet wavelength, visible and infrared.

Documents US2010/0225856A1 US2010/0225876A1 and teach that such a diffraction grating diffracts polarization-splitting an incident light beam, which has any arbitrary polarization state, in a diffracted beam in the order 0, a diffracted beam in the order +1, and/or a diffracted beam in the order -1.

According the same, a diffraction grating polarization-splitting has the following properties:

the sum of the diffraction efficiencies in the order of diffraction and +1-1 in the diffraction order is very high, typically greater than 90%, and

the relative intensities of the diffracted light beams in the diffraction order +1 and in the order of diffraction are -1 function of the state of polarization of the incident light beam, and may vary between 0% and 100% of the total intensity of the diffracted light beams in the order of diffraction and +1 in the diffraction order -1 according to the polarization state of the incident light beam.

However, a spectrometer is generally designed such that a single order, except the diffraction order 0, is operated for the analysis of the upstream light beam.

Therefore, a spectrometer using a diffraction grating polarization-splitting for analyzing the spectrum of a light beam upstream, may have efficiency quasi zero according to the polarization state of the light beam to be upstream least advantageous that a conventional spectrometer using other angular dispersion optimized to means that the evaluation of the diffraction order for the analysis of the upstream light beam is effective.

In order to remedy the disadvantage of the prior art, the present invention provides a spectrometer for operating the very high diffraction efficiency of a bias network polarization-splitting over a wide spectral range.

To this end, the invention relates to a spectrometer for analysing the spectrum of a light beam upstream comprising:

an entry slot adapted to pass said light beam upstream,

angular dispersion means that can be fixed or mobile, adapted to rectified angularly dispersing a light beam as a function of a plurality of wavelengths into a plurality of diffracted light beams,

According to the invention, said means for angular dispersion comprises at least one polarization-splitting diffraction which is adapted, for said plurality of wavelengths, rectified to diffract said light beam into said plurality of diffracted light beams in a same order of diffraction particular from said diffraction grating to polarization separation, which is either the diffraction order + 1, is the -1 diffraction order, when said rectified light beam has a polarization state predetermined rectified which is circular, and said spectrometer further comprises polarization modification means disposed between said inlet slot and said means for angular dispersion, and adapted, for said plurality of wavelengths, to alter the state of polarization of said light beam to generate said upstream light beam according to the rectified rectified predetermined polarization state, said means for modifying the polarization comprising:

means for separating the polarization adapted, for said plurality of wavelengths, to generate, from said upstream light beam, a first light beam and a separate second light beam have separate orthogonal polarization states each other, and

rectification means of the polarization adapted, for said plurality of wavelengths, generating a first rectified polarized light beam from said first separated light beam and a second polarized light beam rectified from said second separate light beam, said first polarized light beam and said second beam rectified rectified polarized light having a same polarization state, said first polarized light beam and said rectified second polarized light beam forming said rectified rectified light beam having the same polarization state.

The spectrometer according to the invention therefore utilizes in combination a diffraction grating polarization-splitting with the means of modifying the polarization of the light beam upstream.

The diffraction grating can be configured to diffract, with a very high efficiency over a very wide spectral band, said light beam rectified into a diffracted light beam, or in order of diffraction + 1, or in order of diffraction -1, rectified if the light beam has a polarization state rectified circular well defined.

The means for modifying the polarization then, irrespective of the state of polarization of the light beam upstream, prepare the polarization state of the light beam according to this polarization state rectified rectified circular well defined, by the polarization-separating means and to the means for rectifying the polarization.

Indeed, irrespective of the state of polarization of the light beam upstream, is separated off by the means for separating the polarization into two separate light beams orthogonal polarization which are each processed by the rectifier means of polarization for polarized light beams that the two rectified have the same circular polarization state that the light beam rectified.

Therefore, the spectrometer according to the invention, allows to exploit the very high efficiency of the diffraction grating at polarization separation in a diffraction order determined, either the order or the order -1 +1 is, regardless of the polarization state of the light beam upstream.

Advantageously, the invention can exploit the very high efficiency of the diffraction grating at polarization separation over a wide spectral range.

Furthermore, other advantageous and non-limiting characteristics of the spectrometer according to the invention are the following:

the spectrometer has a sensing means adapted to measure the light intensity of said plurality of diffracted light beams for each wavelength of the plurality of wavelengths, and to provide a signal representative of the upstream spectrum of said light beam;

the spectrometer comprises means for focusing the plurality of diffracted light beams angularly as a function of said plurality of wavelengths, said focusing means being adapted to focus, for each wavelength of said plurality of wavelengths, said plurality of diffracted light beams on an image plane or on said sensor means;

said means for rectifying the polarization include:

a first optical component of the polarization rectifier adapted, for said plurality of wavelengths, to generate said first polarized light beam rectified from said first separated light beam to said plurality of wavelengths, and

a second optical component of the polarization rectifier adapted, for said plurality of wavelengths, generating said second polarized light beam rectified from said second separate light beam to said plurality of wavelengths;

said polarization-separating means comprise a first optical system adapted to intercept said light beam input before the direct output to at least one optical component polarization separator which is adapted, for said plurality of wavelengths, to generate, upstream from said light beam, said first separate light beam and said second separate light beam;

said first optical system is arranged such that the rays of light said light beam upstream are all parallel to one another to the output of said first optical system, and said polarization-separating means further comprises a second optical system adapted, for said plurality of wavelengths, to intercept input, on the one hand, said first separate light beam to focus on said first optical component bias rectifier and, on the other hand, said second polarized light beam separated to focus on said second optical component bias rectifier;

said optical component polarization separator comprises a Wollaston prism, a Rochon prism, a prism Sénarmont , or a prism beam offset, configured such that said first separated light beam and said second separate light beam have orthogonal linear polarization states, and said first optical component of the polarization rectifier comprises a first quarter wave retarder having a first slow axis and said second optical component of the polarization rectifier comprises a second quarter wave retarder having a second slow axis perpendicular to said first slow axis;

said optical component polarization separator comprises a further diffraction grating polarization-splitting adapted, for said plurality of wavelengths, to diffract said light beam upstream:

separate said first light beam is diffracted in a first diffraction order, which is either the diffraction order +1, either the diffraction order diffraction grating -1 said other polarization-splitting, and having a first circular polarization state, and

separate said second light beam is diffracted in a second diffraction order, which is either the diffraction order +1, either the diffraction order diffraction grating -1 said other polarization-splitting, said second diffraction order is different from the first diffraction order, and having a second circular polarization state orthogonal to said first polarization state, and

said first optical component rectifier polarization comprises a half-wave retardation plate which inverts the state of polarization of said first separate light beam through said first optical component of the polarization rectifier, and said second optical component comprises a polarization rectifier of the neutral blade to parallel faces do not change the state of polarization of said second separate light beam through said second optical component of the polarization rectifier;

the spectrometer includes a plurality of stages cascaded in dispersive configuration additive or subtractive;

advantageously, such as configuration Czerny Turner, said diffraction grating polarization-splitting is rotatably mounted to adjust is the center wavelength of a multichannel sensor, either the wavelength output slot of a single-channel detector;

said means for angular dispersion comprise a prism having an entrance face which intercepts said light beam rectified and an output face on which is disposed said diffraction grating polarization-splitting;

said detection means comprise a multi-channel detector;

said detecting means comprises a slot and a single-channel detector.

Various embodiments of the invention are described in detail with reference to the drawings in which:

figure 1 is a schematic of means for modifying the polarization;

figure 2 is a schematic of means for modifying the polarization according to an embodiment of the apparatus of Figure 1;

figure 3 is a schematic of means for modifying the polarization according to another variant of the device of Figure 1;

figure 4 is a schematic view of a spectrometer according to a first embodiment in a configuration of Czerny-Turner type;

figure 5 is a schematic view of a spectrometer according to an alternate embodiment of the first embodiment comprising a turret multi-network;

figure 6 is a schematic view of a spectrometer according to a second embodiment;

figure 7 is a schematic view of a spectrometer according to a third embodiment with a diffraction grating polarization-splitting transmission-type;

figure 8 is a schematic view of a spectrometer according to a variant of the third embodiment with a diffraction grating polarization-splitting placed on the inclined face of a prism;

figure 9 is a schematic view of a double monochromator comprising two stages-dispersive subtractive configuration;

figure 10 is a schematic view of a double monochromator comprising two stages-dispersive additive configuration;

figure 11 is a schematic view of a triple monochromator comprising three stages-dispersive subtractive configuration;

figure 12 is a schematic view of a triple monochromator comprising three stages additive-dispersive configuration.

The Figures 4 to 12 various embodiments of a spectrometer 100 ; 200 ; 300 ; 500 ; 600 are, intended either for analyzing the spectrum of a light beam 1 upstream (case of embodiments shown in Figures 4 to 8), to either select a portion of the upstream spectrum of a light beam 1 (case of embodiments shown in Figures 9 to 12). In the second case, is then commonly spoken of" monochromators ".

Without limitation, consider is in Figures 1 to 12 that the light beam 1 upstream is non-polarized, that is to say has any arbitrary polarization state. Indeed, without knowledge a priori the polarization state of the light beam 1 upstream, this case is the least restrictive. It will be appreciated to light of the examples, the interest of the invention in respect of that disregard a priori the polarization state of the light beam 1 upstream.

Generally, and as is well shown in Figures 4 to 12, the various embodiments of a spectrometer 100 ; 200 ; 300 ; 500 ; 600 according to the invention comprises first an inlet slot 101.

The entrance slit 101 is a slot shape planar rectangular, centered on an optical axis A1 which is perpendicular to the plane of the entry slot 101.

Consider The in the various embodiments that the light beam 1 upstream is a divergent light beam formed of a cone of light rays, the cone being of revolution about the optical axis A1 and having as vertex the center of the slit input 101.

Thus disposed, the entry slot 101 allowed to pass through the upstream light beam 1.

According to the invention, the various embodiments of a spectrometer 100;

200 ; 300 ; 500 ; 600 shown in Figures 4 to 12 have polarization modification means 1100 which will be described in detail below facing the examples shown in Figures 1 to 3.

These means for modifying the polarization 1100 accept, as input, upstream 1 the light beam that has passed through the slot 101 and generate input, output, rectified a light beam 20 which is also a divergent light beam.

These means for modifying the polarization 1100 are arranged between the entry slot 101, downstream thereof, and various optical elements of the spectrometer 100;

200 ; 300 ; 500 ; 600, these parts comprising means of angular dispersion, that are fixed or can be rotated.

In the particular embodiments of the spectrometer 100 ; 500 ; 600 shown in Figures 4, 5 and 9 to 12, the means for angular dispersion in particular include at least one diffraction grating polarization-splitting 130, 231 ; 531A which is plane and operates in reflection.

In another particular embodiment of the spectrometer 200 shown in Figure 6, the angular dispersion means comprise a diffraction grating polarization-splitting 260 which is concave and operates in reflection.

In another particular embodiment of the spectrometer 300 represented on the Figure 7 and 8, the angular dispersion means comprise at least one diffraction grating polarization-splitting 330, 432 which is plane and operates in transmission.

The dispersion means angular intercept the light beam polarization rectified 20.

The dispersion means disperse angular then rectified 20 angularly the light beam as a function of wavelength.

To simplify and to illustrate the examples of the invention, consider is later on in the description a, two or three particular wavelengths of the spectrum of the light beam 1 upstream for which the light intensity is non-zero.

Note these three particular wavelengths λ1, λ2, λ3 and.

This assumption is not limited and does not or presumes the precise nature of the spectrum of the upstream light beam 1, which can be for example a continuous spectrum, discrete, belt, line or a mixture of all these types of spectrum, and of its spectral range.

It is intended that the means for angular dispersion generate, from the light beam to the rectified 20 wavelengths λ1, λ2, λ3 and:

a diffracted light beam 31 at the wavelength λ1, and

a diffracted light beam 32 to the wavelength λ2 which is angularly separated from the diffracted light beam 31 at the wavelength λ1.

a diffracted light beam 33 at the wavelength λ3 which is angularly separated from the diffracted light beam 31 at the wavelength λ1 32 and the diffracted light beam to the wavelength λ2.

In certain particular embodiments of the invention shown in Figures 4, 5, and 7 to 12, the spectrometer 100 ; 300 ; 500 ; 600 further comprises collimating means 120 ; 320 ; 520 which convert rectified 20 the light beam into a parallel light beam such that all light rays in the light beam 20 are rectified parallel downstream of the collimating means 120 ; 320 and incident on the diffraction grating polarization-splitting plane 130, 231 ; 330, 432 ; 531A with the same incidence.

In the various embodiments of the invention shown in Figures 4 to 12, the spectrometer 100 ; 200 ; 300 ; 500 ; 600 has focusing means 140 ; 260 ; 340 ; 540.

The focusing means 140 ; 260 ; 340 ; 540, which are placed on the optical paths of the diffracted light beams 31, 32, 33, focus, respectively for each wavelength λ1, λ2, λ3, the light beams diffracted 31.32, 33 in an image plane.

In the particular embodiments of the invention shown in Figures 9 to 12, the diffracted light beams 31, 32 are focused on an image plane 505, 605 or at the same point of focus of the image plane 505 (case of Figure 9), are separated from the focus points image plane 505 ; 605 (case of Figures 10 to 12),

In the particular embodiments of the invention shown in Figures 4 to 8, the image plane is for receiving detection means 150.

As is well shown in Figures 4 to 8, the three diffracted light beams 31, 32, 33 are then focused on the image plane into three focus points 41, 42, 43 spatially separated from one another as a function of wavelength λ1, λ2, λ3.

The detection means 150 are sensitive to light intensities of the diffracted light beams 31, 32, 33 focused the focus points 41.42, 43 and then measure the light intensities of the diffracted light beams 31, 32, 33 for each wavelength λ1, λ2, λ3.

The detection means 150 thereby provide a signal representative of the spectrum of said light beam upstream 1 which can then be analyzed.

The different elements provided on the spectrometer 100 ; 300 are included in a frame (not shown) outer opaque to light, the entry slot 101 being located on one of the walls of this frame.

One will now describe the means for modifying the polarization 1100, facing the Figures 1 to 3 on which examples of means for modifying the polarization are represented.

The means for modifying the polarization change 1100, for the plurality of wavelengths λ1, λ2, λ3, the polarization state of the light beam 1 upstream and generate rectified which the light beam 20, is shown in connection with Figures 1 and 2, has a polarization state rectified which is circular.

For this purpose, the means for modifying the polarization 1100 comprise first means for separating the polarization 1110.

As shown in the Figures 1 to 3, these polarization-separating means 1110 is placed downstream of the entrance slit of the spectrometer 100 101;

200 ; 300 ; 500 ; 600, along the optical path of the light beam to intercept 1 upstream thereof.

The polarization-separating means 1110 generate, for each wavelength λ1, λ2, λ3, upstream from the light beam 1 a first separate light beam 11 and a second separate light beam 12 which have polarization states orthogonal to each other.

The means for modifying the polarization 1100 further comprises means for rectifying the polarization 1120 downstream of the polarization-separating means 1110 along the optical paths of the first separated light beam 11 and the second separate light beam 12 which are focused on the means for rectifying the 1120 polarization by the polarization-separating means 1110.

The means for rectifying the output polarization 1120 then generate, for each wavelength λ1, λ2, λ3:

a first polarized light beam 21 rectified from the first separated light beam 11, and

a second polarized light beam 22 rectified from the second separate light beam 12.

According to the invention, the first polarized light beam and rectified 21 the second polarized light beam rectified 22 have a same polarization state that is a circular polarization state and form a light beam by superimposing rectified 20 to the output of the rectifying means 1120 of the polarization.

Therefore, the state of polarization of the light beam 20 rectified rectified is identical to the circular polarization state of the first polarized light beam and rectified 21 of the second polarized light beam 22 rectified.

One will describe below (see examples of Figures 1 to 3) how the polarization-separating means 1110 generate the first separated light beam 11 and the second separate light beam 12 and how the means for rectifying the polarization light beam 1120 generate the rectified 20 having the polarization state rectified is circular.

Preferably in these three examples, the means for rectifying the polarization 1120 include a first component of the optical polarization rectifier 1121 and a second optical component of the polarization rectifier 1122.

The first optical component of the polarization rectifier 1121 and the second optical component of the polarization rectifier 1122 are planar components, located next to one another.

In the first two examples of Figures 1 and 2, the means for rectifying the polarization 1120 are located in the plane of an outlet slot 1101 which is centred on the optical axis A1.

The exit slot 1101 est be real, i.e. formed by means of a physical aperture in a cover means for modifying the polarization 1100 ; or virtual, i.e. that it corresponds to the image of the entrance slit 101 through the polarization-separating means 1110.

In the third example, the means for rectifying the polarization 1120 are located just after the means for separating the polarization 1110 (see detail below).

The first optical component of the polarization rectifier 1121 est arranged to receive said first light beam 11 separate and generates, for each wavelength λ1, λ2, λ3, the first polarized light beam rectified 21;

respectively the second optical component of the polarization rectifier 1122 est arranged to receive said second separate light beam 12 and generates, for each wavelength λ1, λ2, λ3, the second polarized light beam 22 rectified.

In the first example shown in Figure 1, the means for separating the polarization comprise a first optical system 1110 1111 herein comprising a converging lens refracting the upstream divergent light beam 1.

Upon exiting the converging lens 1111, upstream the light beam 1 is directed to an optical component polarization separator 1113.

In this first example, the optical component polarization separator 1113 comprises a Wollaston prism.

It is well known that a Wollaston prism is in fact a parallelepiped formed of two prisms, the parallelepiped having the feature of separating an incident beam of light polarization any two rays of light that are angularly separated and which have linear states of polarization and orthogonal to each other.

Therefore, the Wollaston prism 1113 generates upstream from the light beam 1, at each wavelength λ1, λ2, λ3:

the first separate light beam 11 according to a linear polarization state, and

the second separate light beam 12 according to a linear polarization state orthogonal to the polarization state of the first separated light beam 11.

Alternatively, the optical component polarization separator could for example include a Rochon prism, a prism Sénarmont.

In embodiment, in the first example, the optical component polarization separator could for example include a grating to polarization separation.

In the configuration of the first example of Figure 1 wherein the optical component polarization separator 1113 comprises a Wollaston prism, the first optical component of the polarization rectifier 1121 includes a first quarter-wave retarder and the second optical component of the polarization rectifier 1122 includes a second quarter-wave retarder.

The two waveplates 1121, 1122 are blades made of a uniaxial birefringent crystal.

Conventionally, the first waveplate 1121 thus has first slow axis and the second retardation plate 1122 has a second slow axis.

It is well known in optical a quarter wave retarder converts a linear polarization forming an angle of 45° with the slow axis of the retardation plate in circular polarization, the direction of the circular polarization is achieved by bringing the linear polarization on the slow axis of the quarter-wave plate.

1121 est The first retardation plate positioned relative to the Wollaston prism 1113 so that the first slow axis of the first retardation plate 1121 forms an angle of 45° with the axis of linear polarisation of the first separated light beam 11.

The second retardation plate 1122 est oriented relative to the first waveplate 1121 so that the second slow axis is orthogonal to the first slow axis.

Thus oriented, the second retardation plate 1122 est positioned relative to the Wollaston prism 1113 so that the second slow axis of the second retardation plate 1122 also forms a same angle of 45° with the axis of linear polarisation of the second separate light beam 12, the axis of linear polarisation of the second separate light beam 12 being orthogonal to the axis of linear polarization of the first separated light beam 11.

The thus comprises that:

the first polarized light beam rectified 21, which is generated by transmission of the first separated light beam 11 having a linear polarization state through the first retardation plate 1121 quarter wave, outputs of said retardation plate a circular polarization state, and

the second polarized light beam rectified 22, which is generated by transmission of the second separate light beam 12 having a linear polarization state through the second retardation plate 1122 quarter wave, outputs of said retardation plate a circular polarization state.

Furthermore, as the first separated light beam 11 has a linear polarization state orthogonal to the polarization state of the second separate light beam 12, and as the first slow axis is orthogonal to the second slow axis, the circular polarization states of the first polarized light beam and rectified 21 of the second polarized light beam rectified 22 are identical.

Therefore, as set forth previously, rectified the light beam 20, which is formed of the first polarized light beam and rectified 21 of the second polarized light beam rectified 22, has a circular polarization state.

In a second example shown in Figure 2, the means for separating the polarization 1110 also include a first optical system 1111 herein comprising a converging lens refracting the upstream divergent light beam 1.

1111 The converging lens whose optical axis is coincident with the optical axis A1 is disposed along the optical axis A1 with respect to the entry slot 101 so that the light beam is collimated upstream 1, i.e. the light rays of the light beam upstream 1 are all parallel to one another at the outlet of the converging lens 1111.

Upon exiting the converging lens 1111, 1 upstream the light beam is then directed to an optical component polarization separator 1113 so that the light beam 1 upstream is normally incident on the optical component polarization separator 1113.

In this second example, the optical component polarization separator 1113 here comprises a further diffraction grating polarization-splitting.

Alternatively, in this second example, the optical component polarization separator could include, for example, a Wollaston prism, a Rochon prism, a prism Sénarmont.

Generally, a diffraction grating diffracts an incident light beam into one or more diffracted beams propagating in different directions, i.e. that the diffracted beams are angularly separated.

With reference to the law of diffraction gratings, is then spoken of diffraction orders, such as the order 0 and the higher orders: ±1 orders, orders ±2, etc...

A diffraction grating is generally polarization-splitting a holographic component plane formed of at least a diffractive (" diffractive waveplate " english) liquid crystal.

A diffraction grating has the polarization-splitting feature diffract an incident light beam into at least one diffracted beam in the diffraction order + 1 and a diffracted beam in the diffraction order -1, the two diffracted beams and being circularly polarized orthogonally. For example, if the diffracted beam in the diffraction order +1 is circularly polarized to left, then the diffracted beam in the order of diffraction is circularly polarized -1 right, or vice versa.

This feature exists that the incident light beam is polarized or non-polarized as desired. Indeed, the polarization state of the incident light beam does that governs the distribution of the light energy in the order of diffraction and +1 +1 in the diffraction order.

The other diffraction grating polarization-splitting 1113 est designed to operate on a spectral band covering at least the upstream spectrum of the light 1, such that it has diffraction efficiencies in the order of diffraction and +1 in the diffraction order -1 such that the sum thereof is as close as possible to 100%, typically greater than or equal to 90%, or, preferably, greater than or equal to 95%.

In this way, the diffraction of the light beam 1 upstream by the other diffraction grating polarization-splitting 1113 takes place with a very high efficiency, regardless of the state of polarization of the light beam 1 upstream.

The sum diffraction efficiencies in the order of diffraction and +1 in the diffraction order -1 cannot be equal to 100%. Indeed, not only a portion of the light incident on a diffraction grating polarization-splitting is not diffracted-it is is reflected back, is absorbed, is scattered-, but also a portion of the light incident on a diffraction grating polarization-splitting is diffracted into the diffraction order 0.

Disposed after the converging lens 1111, the other diffraction grating diffracts polarization-splitting 1113, for each wavelength λ1, λ2, λ3 upstream in the light beam 1:

the first separate light beam 11 that is diffracted in a first order diffraction, the diffraction order herein +1 of the other diffraction grating polarization-splitting 1113, and having a first circular polarization state, herein a left hand circular polarization, and

the second separate light beam 12 that is diffracted in a second diffraction order, herein the diffraction order -1 of the other diffraction grating polarization-splitting 1113, and having a second circular polarization state, herein a right hand circular polarization, the second polarization state is orthogonal to the first polarization state.

In this second example, the means for separating the polarization 1110 also include a second optical system 1112 ; formed herein a second lens having an optical axis coincident with the optical axis A1.

The second converging lens 1112 is interposed between the other diffraction grating polarization-splitting 1113 and the means for rectifying the polarization 1120, along the optical paths of the first separated light beam 11 and the second separate light beam 12, for the intercept.

As is well shown in Figure 2, the second lens focuses 1112 then for each wavelength λ1, λ2, λ3:

the first separate light beam 11 on the first optical component of the polarization rectifier 1121, and

the second separate light beam 12 on the second component of the optical polarization rectifier 1122.

In the configuration of the second example of Figure 2 wherein the optical component polarization separator 1113 comprises a further diffraction grating polarization-splitting, the first optical component of the polarization rectifier 1121 comprises a first waveplate half-wave rectifier and the second optical component of the polarization 1122 comprises neutral blade with parallel faces.

It is well known in optics that a retardation plate half-wave transforms, or "reverse", circular polarization to circular polarization orthogonal, i.e. a left hand circular polarization is reversed in a right hand circular polarization, and vice versa.

Furthermore, notice is that a neutral blade to parallel faces is a transparent slide which does not change the state of polarization of a light beam therethrough.

The thus comprises that:

the first polarized light beam rectified 21, which is generated by transmission of the first separated light beam 11 having a left circular polarization state through the half-wave plate 1121, outputs of said half-wave plate a circular polarization state right, and

the second polarized light beam rectified 22, which is generated by transmission of the second separate light beam 12 having a right circular polarization state through the neutral blade 1122 quarter wave, outputs of said neutral blade a right circular polarization state.

Therefore, as set forth previously, rectified the light beam 20, which is formed of the superposition of the first polarized light beam and rectified 21 of the second polarized light beam rectified 22, has a circular polarization state, which is right.

In a third example shown in Figure 3, the means for separating the polarization 1110 comprise, in addition to the first optical system 1111 similar to the first example, an optical component polarization separator 1113 having a prism to beam offset (" beam displacer prism" english).

The prism beam offset 1113 est formed of a birefringent crystal of calcite, of parallelepiped shape and right, 1113A has an input face, an output face 1113B, an upper face and a lower face 1113C 1113D 1113C parallel to the upper face.

1113A The input face and the output face are parallel and 1113B cut such that the optical axis of the crystal forms an angle of 45° with the inlet face 1113A in a plane parallel to the upper face and 1113C 1113D to the underside.

The prism beam offset 1113 upstream 1 separates the light beam, which is collimated normally incident on the input face of the prism 1113A beam offset by the converging lens 1113 1111, into the first separated light beam 11 that is deflected with respect to the light beam 1 and upstream in the second separate light beam 12 which is not diverted by upstream respect to the light beam 1.

For refraction on the exit face of the prism 1113B beam offset 1113, the first separate light beam 11 and the second separate light beam 12 emerge from the prism beam offset 1113 to form two collimated light beams which propagate parallel to one another and in the same direction as the light beam upstream 1.

For propagation in the prism beam offset 1113, the first separate light beam 11 and the second separate light beam 12 are offset and do not overlap at the output of the prism beam offset 1113.

The size of the prism beam offset 1113 along the optical axis A1 can be adjusted so that the offset between the first separated light beam 11 and the second separate light beam 12 is sufficient to separate that the first light beam 11 and the second separate light beam 12 do not overlap at the output of the prism beam offset 1113.

There is provided and a minimum dimension of the prism beam offset 1113 along the optical axis A1.

In output of the prism beam offset 1113, the first separate light beam 11 and the second separate light beam 12 have linear states of polarization, which are orthogonal to each other.

Therefore, the means for rectifying the polarization 1120 are identical to those of the first example shown in Figure 1 and comprise two quarter-wave plates 1121, 1122 aligned such that the polarized light beams rectified 21.22 have a same circular polarization state.

Rectified These polarized light beams 21, 22 are then focused onto the exit slit 1101 by a focusing lens 1130, for forming the rectified 20.

It has now and describe how the spectrometer 100 ; 200 ; 300 ; 500 ; 600 may be generated, for each wavelength λ1, λ2, λ3, from the light beam which has upstream 1 a priori any arbitrary polarization state, a light beam which rectified 20 has a circular polarization state.

Without limitation, consider is later on in the description that the light beam has a rectified 20 circular polarization state which is straight.

One will now include the advantage of such a preparation of the polarization state of the light beam 20 rectified to the light of the description of the angular dispersion means 130 ; 230 ; 330 ; 430 of the spectrometer 100 ; 300 according to the invention.

Indeed, always according to the invention, the means for angular dispersion 130;

230 ; 330 ; 430 comprise at least one diffraction grating polarization-splitting 130 ; 231.232, 233 ; 330 ; 432.

The grating polarization-splitting 130 ; 231, 232, 233; 330;

432 can be of the same type as the other diffraction grating polarization-splitting 1113 of Figure 2.

Preferably, the diffraction grating polarization-splitting 130 ; 231, 232, 233; 330 ; 432 is designed such that it has a very high diffraction efficiency, greater than 90%, more preferably higher than 95% over the entire spectrum of the light beam upstream 1, in a single diffraction order particular, which can be either diffraction order +1, either the diffraction order -1, rectified 20 when the light beam has a predetermined polarization state which is circular. The light beam diffracted in the particular diffraction order by the designed network then has:

a circular polarization state identical to the state of polarization of the light beam 20 rectified when the network operates in reflection, and

a circular polarization state reversed when the network operates to transmission.

Without limitation, consider herein is that the diffraction grating polarization-splitting 130 ; 231, 232, 233; 330 ; 432 is designed such that the diffraction order corresponds to the particular diffraction order + 1, the diffracted light beam in the diffraction order +1 being polarized in a predetermined polarization state which is left circular.

Furthermore, in the spectrometer 100 ; 300 according to the invention, the means for angular dispersion 130 ; 230 ; 330 ; 430 operating in combination with the means for modifying the polarization 1100, the latter are thus configured such that rectified the state of polarization of the light beam corresponds to the rectified 20 predetermined polarization state for which the polarization-splitting 130 ; 231, 232, 233; 330 ; 432 is most effective in the diffraction order +1 particular, in the example above.

Therefore, it will be understood that the diffraction grating polarization-splitting 130 ; 231, 232, 233; 330 ; 432 angular dispersion means 130;

230 ; 330 ; 430 diffracts with a very high efficiency for each wavelength λ1, λ2, λ3 rectified the light beam 20 which has a left circular polarization state, in of the diffracted light beams to said wavelengths in the diffraction order +1.

More specifically, the diffraction grating polarization-splitting 130;

231,232, 233 ; 330 ; 432 diffracts the light beam in rectified 20:

the diffracted light beam 31 at the wavelength λ1,

the diffracted light beam 32 at the wavelength λ2, and

the diffracted light beam 33 at the wavelength λ3.

As will be explained above, these diffracted light beams 31, 32, 33 are then operated by the focusing means 140 ; 340 and the detection means that the spectrometer 150 to 100 ; 300 can scan the spectrum of the light 1 upstream.

The will describe in more detail below the various embodiments of the invention previously described, in which the means for modifying the polarization can be indifferently those of the first example of Figure 1 the second example of Figure 2.

The Figure 3 a spectrometer 100 according to a first embodiment of the invention.

The spectrometer 100 is a type of spectrometer well known, so-called" Czerny-Turner ".

Alternatively, the spectrometer 100 could for example be of type" Ebert-Fastie "," Monk- Gillieson", or" Littrow ".

In this configuration, the collimating means 120 comprise a first spherical concave mirror, the focal plane is situated in the plane of the outlet slot 1101 polarization modification means 1100.

Thus disposed, the first concave mirror 120 rectified 20 collimates the light beam on the diffraction grating polarization-splitting of the spectrometer 100 130 which operates in reflection.

As will be explained previously, the rectified 20 light beam having a polarization state rectified which is circular, the diffraction grating polarization-splitting 130 diffracts the light beam reflection rectified 20 in a single diffraction order, the diffraction order herein + 1, for each wavelength λ1, λ2, λ3 upstream of the light beam 1, thereby giving rise to the three diffracted light beams 31, 32, 33 which are light beams of parallel rays.

Always in this configuration, the focusing means 140 comprise a second spherical concave mirror, which is identical to the first concave mirror 120, of which the focal plane is located in the plane of the detection means 150.

Thus disposed, the second concave mirror 140 focuses the diffracted light beams 31, 32, 33 respectively to the three focus points 41, 42, 43 on the sensing means 150.

The detection means 150 have in this first embodiment a multichannel sensor herein formed of a linear array of CCD sensors placed such that the focus points 41, 42, 43 are aligned on the line CCD sensors.

The focus points 41, 42, 43 are centered on different CCD sensors so that the detector multi-channel 150 delivers a signal relative to the light intensity at the different wavelengths diffracted λ1, λ2, λ3.

This being true for all wavelengths from the spectrum of the light beam upstream 1, the detection means 150 then measure, as a function of wavelength, the light intensities of the light beam 1 upstream to derive its spectrum.

It is further known that the spectral resolution (expressed in nanometers) of a spectrometer is a function of the size of the CCD sensors and their spacing.

Alternatively, the multi-channel detector could for example be formed of a photodiode array, of a two-dimensional array of CCD sensors or photodiodes.

In embodiment, the detection means could comprise a slot and a single-channel detector. The slot has a shape and dimensions which are those of the image of the entrance slit by the collimating optical system, the diffraction grating polarization-splitting and the focusing optical system. The single-channel detector is a single detector, for example a photodiode silicon, germanium, InGaAs, InAs, InSb, PbS, PbSe, or HgCdTe, an avalanche photodiode, a photo-multiplier tube.

The diffraction efficiency of the diffraction grating at polarization separation 130 being very high, the light intensities of the diffracted light beams 31, 32, 33 measured the focus points 41, 42, 43 detection means are very large, and analyzing the spectrum of the light beam 1 upstream is easier.

Furthermore, the spectrometer 100 is, relatively, less sensitive to the ambient light noise.

Finally, it is possible to use only one diffraction grating polarization-splitting 130 to cover a wide spectral range, which may avoid inserting a turret multi-network in the spectrometer 100.

The Figure 4 a spectrometer 100 according to an alternate embodiment of the first embodiment of the invention.

In this embodiment, the spectrometer 100 comprises means for angular dispersion 230 which comprise three diffraction gratings polarization-splitting 231.232, 233.

These three gratings polarization separation 231, 232, 233 are designed such that their spectral bands partially overlap. For example, the first diffraction grating polarization-splitting 231 covers a spectral band ranging from 350 nm to 1000 nm, the second diffraction grating polarization-splitting 232 covers a spectral band ranging from 900 nm to 1800 nm, and the third diffraction grating polarization-splitting 233 covers a spectral band ranging from 1700 nm to 2500 nm.

This allows, on the one hand, cover a spectral band even greater, and, on the other hand, have gratings polarization separation 231, 232, 233 which the efficiency is further optimized on their respective spectral band.

The three gratings polarization separation 231, 232, 233 are in effect attached to the three side faces of a turret multi-network 230A triangular in shape. For rotation of the turret, it is then possible to select in the spectrometer 100, the diffraction grating polarization-splitting 231, 232, 233 to be used according to the spectral band adequate.

Alternatively to the first embodiment of the present invention and its embodiment represented respectively in Figures 4 and 5, wherein the spectrometer 100 is of the type "Czerny-Turner", the spectrometer could for example include a plurality of cascaded stages dispersed additive or subtractive in configuration.

In this embodiment, each of the stages dispersive may include a grating polarization-splitting further, identical to the diffraction grating polarization-splitting means of angular dispersion.

In cascading multiple stages in the additive configuration, can be adding the spectral dispersions of the various stages without degrading the overall transmission in the spectrometer by the use of the diffraction gratings to polarization separation.

In cascading multiple stages in the subtractive configuration, it is possible to realize a tunable filter high spring rate, while maintaining excellent transmission through the spectrometer.

The Figure 6 a spectrometer 200 according to a second embodiment of the invention.

The spectrometer 200 260 comprises a hybrid optical component of the angular dispersion means and the focusing means.

The hybrid optical component 260 is formed of a diffraction grating with polarization separation which operates in reflection and that is non-planar but has a shape for example spherical or concave so that the light beam is diffracted simultaneously rectified 20 and focused by the hybrid optical component 260 on the sensing means 150.

The configuration of the second embodiment is particularly advantageous in terms of the space and adjusting the by reducing the number of components used in the spectrometer 200.

The Figure 7 a spectrometer 300 according to a third embodiment of the invention.

The collimating means 320 of the spectrometer 300 comprise a first convergent lens, the focal plane is situated in the plane of the outlet slot 3101 polarization modification means 1100 so that the first lens collimates the light beam 320 rectified 20 on the diffraction grating polarization-splitting of the spectrometer 300 330 which operates in this embodiment in transmission.

340 The focusing means comprise a second convergent lens, the focal plane is substantially coincident with the plane detection means 350 that are identical to the sensing means 150 of the spectrometer 100 shown in Figure 3.

Thus disposed, the second lens 340 focuses the diffracted light beams 31, 32, 33 respectively to the three focus points 41, 42, 43 on the detection means 350.

Alternatively, and advantageously, the collimating means and the focusing means could for example include complex optical systems with more lenses for correcting the geometric and chromatic aberrations over a wide spectral range for the light beams and having a divergent upstream.

Are observed in Figure 5 that the assembly of the elements of the spectrometer 300 is not aligned in a same direction, such as the optical axis A1. In some configurations, nevertheless may be desirable to have a spectrometer "online", for example due to the amount of space required, or when transforming a camera imaging spectrometer.

This represented in Figure 8 a spectrometer 300 according to one variation of the second embodiment of the invention.

Angular dispersion The means 430 431 comprises a prism and a diffraction grating polarization-splitting diffraction grating 432 identical to the polarization-splitting of the spectrometer 300 330 shown in Figure 5.

The prism 431 is a right-angle prism which has:

an input face 431A perpendicular to the optical axis A1 and facing the first lens 320, so that the rays of the light beam 20 are rectified normally incident on this input face of the prism 431 431A,

a base 431B perpendicular to the input face 431 A, and

an output face opposite 431C and inclined with respect to the input face 431A and forming an angle therewith of  prism.

Advantageously, the different faces 431A, 431 B, 431C of the prism 431 are processed anti-reflection.

As shown in Figure 6, the diffraction grating polarization-splitting 432 is arranged on the side of inclined 431C output of the prism 431, bearing on it by means of an optical adhesive.

Alternatively, the diffraction grating polarization-splitting could for example be located on the input face of the prism, bearing on it by means of an optical adhesive.

In embodiment, could be making the diffraction grating polarization-splitting directly on the outlet face or on the input face of.

 The prism angle is determined such that the diffracted light beam 32 for a wavelength λ2 herein located substantially in the center of the upstream spectrum of the light 1 is collimated along the optical axis A1.

In this way, by placing the second lens 340 such that its optical axis is parallel to the optical axis A1, the three focus points 41.42, 43 are located in a plane perpendicular to the optical axis A1. The detection means 150 are then aligned and centered along the optical axis A1.

Therefore, the prism 431 introduces a deflection to compensate for angular that introduced by the diffraction grating polarization-splitting 432 in order that the various elements of the spectrometer 300 are aligned in one and the same direction, herein along the optical axis A1.

This therefore provides a spectrometer "online".

In other alternative embodiments of a spectrometer, the collimating means and/or the focusing means are designed and arranged to form an image of the outlet slot polarization modification means.

In the case of Figures 1 to 3, the means for modifying the polarization 1100 are then such that the first polarized light beam and rectified 21 the second polarized light beam 22 are respectively rectified imaged by the collimating means 120 ; 320 and/or the focusing means 140 ; 260 ; 340 at two separate points detection means 150, which can then be measured separately their respective intensities.

Rectified The first polarized light beam 21 and the second polarized light beam rectified 22 each having a polarization state function of the state of polarization of the light beam 1 upstream, it is possible, knowing the configuration of the means for modifying the polarization, to deduce therefrom the state of polarization of the light beam 1 upstream.

Therefore, a spectropolarimeter.

The Figure 9 a first dispersive monochromator 500 comprises two stages 500Α , successive 500B which are cascaded in subtractive configuration.

The monochromator 500 has an entrance slit 101 and polarization modification means 1100 similar to those of spectrometers 100, 200, 300 of the three embodiments of a spectrometer previously described.

It further comprises means collimating 520, herein formed of a first concave mirror, to collimate the light beam 20 from rectified polarization modification means 1100.

Similarly, the monochromator 500 has focusing means 540 provided herein a second concave mirror, identical to the first concave mirror 520, focusing the light beam from the second stage on a dispersive 500B image plane 505.

Dispersive 500A The first stage and the second stage dispersive 500B are located, along the light beam, between the first concave mirror and the second concave mirror 520 540.

As shown in Figure 9, the first stage dispersive 500A comprises:

a first diffraction grating polarization-splitting 531A operating in reflection,

a third concave mirror 502A, identical to the first concave mirror, and

a first plane mirror 503A.

The first diffraction grating polarization-splitting 531A is positioned in the monochromator 500 to intercept the collimated beam of light by the first concave mirror 520.

The first diffraction grating polarization-splitting 531A then diffracts the collimated light beam as a function of the wavelength of the diffracted light beams 31.32.

For sake of clarity, is represented in Figure 9 that two diffracted light beams diffracted 31.32 respectively to the wavelengths λ1 and λ2.

For because of its size, the light beams diffracted 31.32 are then folded by reflection on the third concave mirror 502A and on the first plane mirror 503A.

In dispersive 500A output of the first stage and upstream of the second stage dispersive 500B, a filtering slot 501 is positioned along the optical path of the diffracted light beams 31.32.

The filtering slot 501 is operable to spatially filter the diffracted light beams 31, 32 and to reduce the stray light propagating in the monochromator.

More generally, the filtering slot 501 may include a mask having a plurality of openings for simultaneously selecting multiple spectral bands well defined according to the dimensions of the respective openings and their spacing.

Alternatively, the filtering slot could include another type of mask having a plurality of openings to perform a function of spectral filter optionally complex.

Similarly dispersive 500A to the first stage, the second stage dispersive 500B comprises:

a second plane mirror 503B,

a fourth concave mirror 502B, the same as the third concave mirror, and

a second grating polarization-splitting 531 B, identical to the first and also functioning in transmission,

503B The second plane mirror reflects the diffracted light beams 31, 32 filtered by the filtering slot 501 in the direction of the fourth concave mirror 502B, thereof folding the diffracted light beams 31, 32 and directed towards the second diffraction grating polarization-splitting B 531.

The second diffraction grating diffracts polarization-splitting 531B then a second time the light beams diffracted 31.32.

Since above described, according to the first embodiment of a monochromator, the two stages dispersive 500Α , 500B are subtractive configuration.

This means that the monochromator 500 is configured such that the second stage dispersive 500B compensates for the dispersion of the dispersive 500A first stage.

In particular, herein, the second diffraction grating polarization-splitting 531B is oriented so that the diffracted light beams 31, 32 incident on this second diffraction grating polarization-splitting 531B after reflective diffraction are superimposed on the second diffraction grating polarization-splitting 531B and form a 20A emergency light beam which is a collimated beam.

For this purpose, the orientation of the second diffraction grating polarization-splitting 531B is obtained by rotation of 180° of the first diffraction grating polarization-splitting 531A about the optical axis A1 polarization modification means 1100.

Therefore, the light beam from the second stage dispersive 500A can then be focused by the focusing means 540 on the image plane 505.

A variant first embodiment of a monochromator

The Figure 10 an alternate embodiment of the first 500 dispersive monochromator comprising two stages 500Α , successive 500B which are cascaded in additive configuration.

The embodiment includes the same elements as the monochromator 500 of Figure 9.

However, the configuration of the alternate embodiment of the first 500 monochromator is such that the orientation of the first diffraction grating polarization-splitting 531A is the same as that of the second diffraction grating polarization-splitting B 531.

In these conditions, the second diffraction grating polarization-splitting 531B only compensate more diffraction by the first diffraction grating polarization-splitting 531A but, on the contrary, double the dispersion of the diffracted light beams 31, 32 so that they are separated into dispersive 500B output of the second stage.

The second concave mirror 540 then focuses the light beams diffracted 31.32 focus points in two distinct image plane 505.

The Figure 11 a second embodiment of a dispersive monochromator 600 comprising three successive stages:

dispersive 600A a first stage and a second stage dispersive 600B subtractive cascaded configuration, and

a third stage dispersive 600C simple.

In this second embodiment, the various elements are located either upstream or downstream of the various stages are identical to the dispersive elements of the first embodiment of a monochromator 500 shown in Figure 9.

Similarly, the first stage is identical to the first dispersive 600A 500A dispersive stage of the first embodiment of a monochromator.

The second stage dispersive 600B includes not only all of the elements of the second stage dispersive 500B the first embodiment of the monochromator 500, but also a fifth concave mirror and a plane mirror 602C fourth 603C.

Dispersive 600A The first stage and the second stage being dispersive 600B cascaded in subtractive configuration, the beam obtained by diffraction on the second diffraction grating is polarization-splitting 531B the the emergency light beam collimated 20A.

As in the first stage dispersive 600A, the light beam collimated emerging 20A is folded by the fifth concave mirror and reflected by the third mirror plane 603C.

The liquid then passes through a second filtering slot 601 located along the optical path, between the second stage and the third stage dispersive 600B dispersive 600C.

The third stage dispersive 600C is a conventional dispersive stage here comprises a fifth plane mirror 603D, a sixth concave mirror 602D and a dashed grid 631C may have a very highly dispersive.

Alternatively, the third stage dispersive could include, for example, a diffraction grating polarization-splitting, which would otherwise be identical to the first diffraction grating.

The interest of a monochromator such as that described in Figure 11 is to provide a monochromator that disperses in the image plane 505 a small spectral band with the same dispersion that in the plane of the filtering slot 501 (if the focal stages are the same), but with a degree of stray light much lower, due to the dual filtering in the plane of the filtering slot 501 and in the plane of the second filtering slot 601

The Figure 12 a variant of the second monochromator 600 comprising:

dispersive 600Α two stages, successive 600B cascaded configuration which are additive, and

-a third stage dispersive 600C identical to that of the monochromator 600 shown in Figure 11.

The interest of a monochromator according to the variant shown in Figure 12 is to provide a monochromator which adds the dispersions of the three stages, and attains large dispersion with a degree of stray light very low, much lower than could be using a single stage three times more dispersive.