Method for increasing signal to noise ratio of femtosecond laser through F-P (Fabry-Perol) etalon internally installed with electro-optic crystal
Technical Field The invention relates to a lifting femto second laser signal-to-noise ratio of the order of the method and its device, in particular to a kind of electro-optical crystal F-P through the built-in (Fabry-Perot) etalon with multiple cavities of the lifting magnitude femto second laser signal-to-noise ratio of the method and device for implementing the method, which belongs to the technical field of ultra-short pulse. Background Art In recent years, as the chirped pulse amplification (CPA) technology, high power ultra-short pulse laser system achieved rapid development. The use of nd glass laser device of the order of magnitude of kJ, the output laser pulse peak power PW magnitude can be achieved, the focusing light intensity can reach 1021-22 W/cm2 magnitude. The interaction of the laser and then, when the laser intensity reaches 1013 W/cm2 time, plasma can be generated, even if the laser intensity is smaller than 1013 W/cm2, if the and then a sufficient interaction time, also can generate plasma. The focusing strength is 1022 W/cm2 the purposes of the target pulses, pulse its pre- can not be higher than the strength of the 1013 W/cm2, otherwise, it will damage the interaction of the main pulse condition of the target, thus requiring such laser system of the signal-to-noise ratio reaches 1010 the above, therefore, it was necessary to study how to improve the signal to noise ratio of the ultra-short pulse laser. At present, for a lifting ultra-short pulse signal-to-noise ratio of the method are mainly the following: (I) cross-polarized wave (XPW) method Because the cross-polarized wave is produced a four-wave mixing process, derived from crystal third-order nonlinear tensor real part of the anisotropic. Cross-polarized wave is generated in the input pulse intensity is proportional to three source, which can effectively improve its signal-to-noise ratio. V.Chvykov using cross-polarized wave, the signal-to-noise ratio over the 4 level magnitudes, thus obtaining signal-to-noise ratio as high as 1011 the 50TW laser pulse (V.Chvykov, P.Rousseau, S.Reed, et al.Generationof1011 contrast 50 TW laser pulses[J] .Optics Letters, 2006, 31 (10): 1456-1458). (Ii) saturable absorber ( Absorber Saturable) method To Hong Kyung-Han 1KHz μ J levels of the repetition rate of the energy injection system, and utilizes a method to achieve saturated absorption 4 × 108 signal-to-noise ratio, the signal-to-noise ratio improves the 400 times (K.H.Hong, B.Hou, J.A.Nees, et al.Generation and measurement of > 108 intensity contrast ratio in a relativistic kHzchirped-pulse amplified laser[J] .Applied physics B, 2005, 81 : 447-457). However, the saturable absorber will appear non-linear phase shift, thereby causing the deformation of the beam space outline, and the non-linear saturated absorption peak power of over most of the medium will normally be a self-focusing required energy, the same will also cause a distortion of the beam space outline. (Iii) plasma mirror ( Mirror Plasma) filtering method Since the plasma mirror to the higher the intensity of the pulse of the low reflectivity, and vice versa. Therefore, it may be used to remove the small intensity of the prepulse, so that the signal-to-noise ratio the input signal to 2 orders of magnitude [Yutaka Nomura, LaszloVeisz, Karl Schmid, et al. Time-resolved reflectivity measurements on a laser mirror plasma pulses[J withfew-cycle] Physics of Journal .New, 2007, 9:1-8]. G.Doumy, and [G.Doumy, Ph.Martin, M.Pedrix, et al.Practical double plasma-mirror pulse cleaner forhigh-intensity femtosecond laser-plasma harmonics.Quantum Electronics and Laser ScienceConference (QELS), 2005 : 2021-2023] the double-plasma mirror filtering method the contrast enhancing the 4 × 104 times, to obtain more than 1011 signal-to-noise ratio. However, the existence of plasma mirror filtering of low conversion efficiency, the light path adjustment is complicated and the like. Content of the invention The purpose of this invention is to overcome the above-mentioned the defects in the prior art, to provide a of the electro-optical crystal through the built-in lifting etalon with multiple cavities F-P method for femtosecond laser signal-to-noise ratio and the device for implementing the method. The present invention provides method and apparatus for high efficiency can be realized by the femto-second laser signal and filtering the noise, thereby effectively improving the purpose of femtosecond laser signal-to-noise ratio. Optical principle of the present invention is a comprehensive utilization F-P (Fabry-Perot) etalon of the interference effect and crystal electro-optic effect of femtosecond laser to enhance the signal-to-noise ratio. Its basic thought is: firstly, the femtosecond laser light source output to raise by femtosecond laser signal-to-noise ratio, containing the pulse chirp signal chirp and the noise of the signal light; and then through the electro-optic crystal at different times different voltage is applied on both ends, in order to change two adjacent etalon F-P phase difference through the light beam, thereby forming a scanning through the spectrum of this nature, and the etalon F-P with different at different times the instantaneous through the spectrum. When the instantaneous etalon F-P through the center frequency of the spectrum is at any time with the change of speed between the pulse chirp signal between the instantaneous frequency at any time the rate of change of the chirp the same size, greatly can be realized for filtering out the noise light, and high efficiency through the signal light, the chirp of the signal light so as to enhance the purpose of the signal-to-noise ratio; final, then the signal-to-noise ratio after the upgrade into the wave front aberration chirp signal femto-second laser having a high signal-to-noise ratio. In order to realize the above-mentioned purpose, this invention adopts the following measures to be realize the technical scheme. The present invention provides built-in the electro-optical crystal of the adoption of standard F-P raising method for femtosecond laser signal-to-noise ratio, comprising the following steps: (I) will be to raise the femto-second laser signal-to-noise ratio of the optical pulse stretcher for stretching, containing the pulse chirp signal chirp and the noise of the signal light; (Ii) through the electro-optic crystal at different times different voltage is applied on both ends, that is, according to formula Voltage control function, the etalon F-P have different instantaneous through the spectrum, and the center frequency of the instantaneous through the spectrum at any time the rate of change in the chirp of the signal pulses between the instantaneous frequency at any time the rate of change in the chirp of the same size, so as to greatly filtrated the noise light, and through the signal light with high efficiency, so as to effectively improve the signal to noise ratio of the chirp signal light; The final (iii) using optical pulse compressor, the signal-to-noise ratio after the upgrade into the wave front aberration chirp signal femto-second laser having a high signal-to-noise ratio. In the above-mentioned technological scheme, for the different moments applied on both ends of the electro-optical crystal 0-13kV different voltage within the range of. The invention to achieve the above-mentioned improved method for femtosecond laser signal-to-noise ratio of the device, along the light propagation direction, in other words, Z direction, comprises generating an initial signal-to-noise ratio to raise femtosecond laser light source of the signal light, the optical pulse stretcher, etalon F-P F-P plate and 1st 2nd a standard tool, the electro-optical crystal, high-voltage pulse power supply, optical component such as optical pulse compressor; states the femtosecond laser light source output of the femto-second laser light pulse stretcher stretching to make it form containing chirp signal pulse and the noise of the optical chirp signal; then, the light source is made incident upon a chirp signal etalon F-P 1st a board, and by the high-voltage pulse power supply to drive the electro-optical crystal, the etalon F-P emergent a 2nd; finally, optical chirp signal compressed through the optical pulse compressor of the femtosecond laser with high signal-to-noise ratio. In the above-mentioned technological scheme, generates an initial signal light of the femtosecond laser light source is titanium sapphire laser. In the above-mentioned technological scheme, of the etalon F-P plate 1st and 2nd F-P etalon by a plate positioned in parallel to each other. In the above-mentioned technological scheme, the etalon F-P plate 1st and 2nd F-P of a standard tool opposite the surface is coated with a silver film of high reflectance, or aluminum film. In the above-mentioned technological scheme, the electro-optical crystal adopts the phosphoric acid two deuterium potassium (KD* P), or ammonium dihydrogen phosphate (ADP), or potassium dihydrogen phosphate (KDP). In the above-mentioned technological scheme, the optical pulse stretcher by the grating to form, or is composed of a prism to form. In the above-mentioned technological scheme, the optical pulse compressor to form by the grating, or is composed of a prism to form. Compared with the prior art, the present invention has the following beneficial technical effect: 1, the invention is based on the built-in the electro-optical crystal of the etalon with multiple cavities F-P femto second order of magnitude of laser signal-to-noise ratio and implementing the method for method for the experimental device, after filtering of the signal to noise ratio of the signal-to-noise ratio than the original lifting two orders of magnitude. 2, the invention is based on the built-in the electro-optical crystal of the etalon with multiple cavities F-P femto second order of magnitude of laser signal-to-noise ratio and implementing the method for method for the experimental device, not only can effectively improve the femto second laser signal-to-noise ratio, but also, the signal light through the efficiency is very high, can reach 95% or more. 3, the present invention based on the built-in the electro-optical crystal of the etalon with multiple cavities F-P femto second order of magnitude of laser signal-to-noise ratio, has the advantages of simple structure, convenient to adjust the device. Description of drawings Figure 1 is a schematic diagram of the principle of the invention based on the built-in the electro-optical crystal of the etalon with multiple cavities F-P method for femtosecond laser signal-to-noise ratio; Figure 2 is a structure diagram of apparatus for implementing the invention based on the built-in the electro-optical crystal of standard F-P raising method for femtosecond laser signal-to-noise ratio. In the Figure, 1-chirp signal pulse; 2-to-noise ; the instantaneous by spectrum etalon 3-F-P; the instantaneous etalon 4-F-P through spectral scanning path; I-laser intensity; t-time ; ω-angular frequency; 5-femtosecond laser light source; 6-optical pulse stretcher; 1st block plate etalon 7-1-F-P; 2nd assembled etalon 7-2-F-P; 8-the electro-optical crystal; 9-high-voltage pulse power source; 10-optical pulse compressor. Mode of execution Attached Figure below, and through the specific embodiment to the invention the method and the device for further detailed description, but it is only used to illustrate the invention a number of specific embodiments, but this invention should not be understood as any limitation of the scope of protection. The invention is based on the built-in the electro-optical crystal of the etalon with multiple cavities F-P femto second order of magnitude of laser signal-to-noise ratio as shown in Figure 1. the principle of the method Figure 1 in, said laser beam intensity I, t for time, of the angular frequency ω is; different times the instantaneous etalon F-P through the spectrum 3 different, the instantaneous etalon F-P through the spectrum 3 scanning path 4 in the direction as shown by an arrow, instantaneous through the spectrum 3 for pulse chirp signal at the same time 1 and noise 2. However, due to transient through the spectrum 3 the rate of movement at any time of the chirp signal pulse 1 time of the instantaneous frequency with the rate of change of the chirp of the same size, so that the chirp signal pulse 1 through with high efficiency; but the noise 2 of the instantaneous frequency of the instantaneous rate of change of the time through the spectrum 3 the rate of movement at any time is not consistent between, so that the transmittance is very low, so that the femto-second laser signal-to-noise ratio can be improved. The invention is based on the built-in the electro-optical crystal of the etalon with multiple cavities F-P magnitude femto second laser signal-to-noise ratio to provide the structure of the device of the method as shown in Figure 2. Along the light propagation direction, in other words, Z direction, comprises generating an initial signal-to-noise ratio to raise femtosecond laser light source of the signal light 5, optical pulse stretcher 6, with standard F-P plate 1st 7-1, the electro-optical crystal 8, high-voltage pulse power supply 9, assembled with standard F-P 2nd 7-2, optical pulse compressor 10. The generated initial signal-to-noise ratio to raise femtosecond laser light source of the signal light 5 of the femtosecond laser output of the optical pulse stretcher 6 stretching, containing the pulse chirp signal chirp and the noise of the signal light; and then, the light source is made incident upon a chirp signal 1st block plate etalon F-P 7-1, and by the high-voltage pulse power supply 9 driving the electro-optical crystal 8 the rear, and then assembled from standard F-P with 2nd 7-2 exit; finally, the signal-to-noise ratio after the upgrade optical chirp signal optical pulse compressor 10 is compressed into the femto second laser having a high signal-to-noise ratio. The device of the invention wherein the high-voltage power supply in the control steps are as follows: (I) assembled from standard F-P with 2nd 7-2 transmission of light of the multi-beam interference field duplicate amplitude can be expressed as: In the formula: ρ is the standard F-P has plates a silver or aluminum film of the reflectance of the surface of in opposite directions, For the phase difference of two adjacent transmission light beam; (Ii) by (1) type can be obtained with standard F-P 2nd a board 7-2 the transmitted light intensity is: Thus with standard F-P 2nd a board 7-2 through the spectrum of the function is: The (iii) with internal standard F-P the both ends of the electro-optical crystal of the electric field, the main refractive index change is: Therefore, assembled from standard F-P with 2nd 7-2 output of the phase difference of two adjacent transmission light beam for: (4) In the formula: for Δn electro-refractive index change, is a reflection φ phase change, for L 1st block plate etalon F-P 7-1 and 2nd a board 7-2 distance between two parallel plates, the electro-optical crystal length d; (IV) the above-mentioned phase difference (4) substituted into the formula (3) with standard F-P formula obtained through spectral function of T, when the signal wavelength λ (t) chirp t the change with time, should be correspondingly changed voltage of two ends of the electro-optical crystal of V (t), make the corresponding signal corresponding to a time the transmittance of the optical wavelength The electro-optic crystal can be obtained on the time change of the voltage of the expression: Thus when the voltage control function of the rate of change of the time of the chirp of the signal pulses is identical twitter rate , can make the chirp signal pulse through an efficient manner, but the noise is filtered out, and thereby to enhance the signal to noise ratio of the chirp signal light. Embodiment 1 According to Figure 2 the various optical element mounting structure, the etalon F-P plate 1st 7-1 and 2nd a board 7-2 the opposite surface of the two parallel plates coated with a reflectance is 0.96 of silver film, the electro-optical crystal 8 by phosphoric acid two deuterium potassium (KD* P) making, the length is 3 cm, the electro-optical coefficient 23.6 × 10-12 V/m, F-P standard with the distance between the two plates than KD* P long the 6 m, optical pulse stretcher 6 and optical pulse compressor 10 is composed of two antiparallel the arrangement of the grating of the diffraction grating, the density of lines of the diffraction grating 600 lines/mm. The laser light source states the femtosecond 5 adopts the 800 nm titanium sapphire of the center wavelength of the ultra-short pulse laser light source, an initial pulse width 50fs, bandwidth 18.7 nm. The chirped pulse stretch the relationship between the front and back pulse can be expressed by the following formula: In the formula, ΔT0 and respectively Δ T of the chirped pulse stretching and pulse width, C to chirped pulse chirp parameter. After the stretch the pulse width 1ns, the intensity of peak value 450Mw/cm2, chirp coefficient is 20000. When the initial signal-to-noise ratio for 108 chirp pulse injection-built-in KD* P F-P standard desk of, by adjusting the high-voltage pulse power supply 9, to make to exert in KD* P the voltage on V (t)-2317V/ns to slope is the linear form of 0-5kV change in the voltage range, in order to the chirp signal pulse chirp same size, after filtering by the spectrum of the chirped pulse signal-to-noise ratio is about 3 × 1010, signal-to-noise ratio comparing the initial signal-to-noise ratio 108 lifting about 300 times, that is, the signal-to-noise ratio improves the 2 level magnitudes, and, chirp of the signal light through the efficiency can be as high as 95% or more. Embodiment 2 In the embodiment of this case will be 1 to replace the electro-optical crystal used in the ammonium dihydrogen phosphate (ADP), the embodiment of other conditions are 1 the same, when the initial signal-to-noise ratio for 108 chirp pulse-injection in the ADP F-P standard tool, by adjusting the high-voltage pulse power supply 9, to make to exert in KD* P the voltage on V (t)-6308V/ns to slope is the linear form of 0-13kV change in the voltage range, in order to the chirp signal pulse chirp same size, after filtering by the spectrum of the chirped pulse signal-to-noise ratio is about 3 × 1010, signal-to-noise ratio comparing the initial signal-to-noise ratio 108 lifting about 300 times, that is, the signal-to-noise ratio improves the 2 level magnitudes, and, chirp of the signal light is also through efficiency can be as high as 95% or more. Embodiment 3 In the embodiment of this case will be 1 to replace the electro-optical crystal used in the potassium dihydrogen phosphate (KDP), pulse stretcher 6 and the pulse compressor 10 is composed of two antiparallel the arrangement of the prism, the embodiment of other conditions are 1 the same, when the initial signal-to-noise ratio for 108 chirp pulse-injection in the ADP F-P standard tool, by adjusting the high-voltage pulse power supply 9, to make to exert in KD* P the voltage on V (t)-5160V/ns to slope is the linear form of 0-10kV change in the voltage range, in order to the chirp signal pulse chirp same size, after filtering by the spectrum of the chirped pulse signal-to-noise ratio is about 3 × 1010, signal-to-noise ratio comparing the initial signal-to-noise ratio 108 lifting about 300 times, that is, the signal-to-noise ratio improves the 2 level magnitudes, and, chirp of the signal light is also through efficiency can be as high as 95% or more. The invention relates to a method for increasing the signal to noise ratio of a femtosecond laser through an F-P (Fabry-Perol) etalon internally installed with an electro-optic crystal and a device thereof, which belong to the technical field of ultrashort pulses. The method comprises the following steps: firstly, stretching a femtosecond laser pulse to be increased in the signal to noise ratio, which is output from a femtosecond laser light source, into chirp signal light; enabling an instaneous spectral filtering function output by the F-P etalon to be consistent with the chirp size of the chirp signal light by modulating the voltages of both ends of the electro-optic crystal internally installed in the F-P etalon, and thereby, a chirp signal pulse efficiently pass, whereas noise is filtered off to achieve the goal of increasing the signal to noise ratio of the chirp pulse; finally, compressing the chirp signal light into the femtosecond laser with higher signal to noise ratio. The device for realizing the method comprises the femtosecond laser light source, a laser pulse stretcher, the F-P etalon, the electro-optic crystal, a high-voltage pulse power supply, a laser pulse compressor and the like. The signal to noise ratio of the femtosecond laser can be effectively increased by adopting the method and the device. Moreover, the device has simple structure and convenient adjustment. 1. A electro-optical crystal through the built-in lifting etalon with multiple cavities F-P method for femtosecond laser signal-to-noise ratio, which is characterized in that the method comprises the following steps: (I) will be to raise the femto-second laser signal-to-noise ratio of the optical pulse stretcher for stretching, containing the chirp signal pulse (1) and noise (2) chirp signal light; (Ii) through the electro-optic crystal for at different moments (8) different voltage is applied on both ends, that is, according to formula Voltage control function, the etalon F-P have different instantaneous through the spectrum (3), and the instantaneous through the spectrum (3) of the center frequency of the rate of change with time of the chirp signal pulse (1) of the instantaneous frequency of the chirp the time rate of change of the same size, in order to filter off signal light and the noise light, optical chirp signal effectively increase the signal-to-noise ratio; The final (iii) using optical pulse compressor (10), the signal-to-noise ratio after the upgrade into the wave front aberration chirp signal femto-second laser having a high signal-to-noise ratio. 2. Method according to Claim 1, characterized in that the different moment in the electro-optical crystal (8) is applied on both ends of the 0-13kV different voltage within the range of. 3. A electro-optical crystal through the built-in lifting etalon with multiple cavities F-P device for femtosecond laser signal-to-noise ratio, along the light propagation direction, in other words, Z direction, comprises generating an initial signal-to-noise ratio to raise femtosecond laser light source of the signal light (5), the optical pulse stretcher (6), with standard F-P plate 1st (7-1) and standard F-P with 2nd a board (7-2), the electro-optical crystal (8), high-voltage pulse power source (9) and an optical pulse compressor (10); the lifting signal-to-noise ratio to femtosecond laser light source (5) of the femtosecond laser output of the optical pulse stretcher (6) stretching the chirp signal light is formed; the light source is made incident upon a chirp signal etalon F-P plate 1st (7-1), and by the high-voltage pulse power source (9) driving the electro-optical crystal (8) the rear, and then assembled from standard F-P with 2nd (7-2) exit; the final chirp signal light through the optical pulse compressor (10) is compressed into the femto second laser having a high signal-to-noise ratio. 4. Device according to Claim 3, characterized in that the initial signal light of femtosecond laser light source (5) is titanium sapphire laser. 5. Device as in Claim 3 or Claim 4, characterized in that the standard F-P of the plate 1st (7-1) and a 2nd F-P etalon (7-2) is a flat plate arranged in parallel to each other. 6. Device as in Claim 3 or Claim 5, characterized in that the plate 1st F-P etalon (7-1) and standard F-P with 2nd a board (7-2) the opposite the surface is coated with a silver film of high reflectance, or aluminum film. 7. Device according to Claim 3, characterized in that the electro-optical crystal (8) a phosphoric acid two deuterium potassium (KD* P), or ammonium dihydrogen phosphate (ADP), or potassium dihydrogen phosphate (KDP). 8. Device according to Claim 3, is characterized in that the optical pulse stretcher (6) to form by the grating, or is composed of a prism to form. 9. Device according to Claim 3, is characterized in that the optical pulse compressor (10) to form by the grating, or is composed of a prism to form.