CN114326254A - Femtosecond double-switch optical Kerr gate based on optical birefringence effect and implementation method - Google Patents
Femtosecond double-switch optical Kerr gate based on optical birefringence effect and implementation method Download PDFInfo
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Abstract
The invention discloses a femtosecond double-switch optical Kerr gate based on optical birefringence effect and a realization method thereof, wherein two switch pulse lights with mutually vertical polarization and specific time delay are generated by a birefringent crystal, the time delay of the two pulses is 140fs, and the adjustment of the intensities of the two switch pulse lights is realized by the combination of a half-wave plate and the birefringent crystal. The optical axis direction of the birefringent crystal is 45 ° to the polarization direction of the probe light. By introducing the second switch pulse light and continuously adjusting the intensity of the second switch pulse light relative to the first switch pulse light through rotating the half-wave plate, the optical Kerr gate can be effectively controlled by the second switch pulse light at the closing stage of the first switch pulse excitation, so that the transmittance of the optical Kerr gate is mainly determined by the first switch pulse light, the closing time of the optical Kerr gate is greatly shortened under the regulation and control of the second switch pulse light, and the high transmittance and the ultra-fast switching time of the femtosecond optical Kerr gate are further realized simultaneously.
Description
Technical Field
The invention belongs to the technical field of ultra-fast imaging and measurement, and relates to a femtosecond double-switch optical Kerr gate based on an optical birefringence effect and an implementation method thereof.
Background
The development of ultra-fast imaging and measuring technology has important application value in the research fields of transient processes such as high-speed collision, detonation process, high-voltage discharge, vision mechanism and the like. Generally, high time resolution imaging from millisecond to subpicosecond can be realized by utilizing a photoelectric technology, however, in the research fields of molecular structure dynamics, ultra-fast surface vibration process, extreme time resolution fluorescence microscopy, identification of objects in a strong scatterer and the like, ultra-fast imaging technology based on photon technology, such as femtosecond holographic imaging and nonlinear optical gate gating imaging technology, must be used.
The optical Kerr gate gating imaging technology is a typical nonlinear optical gate gating imaging technology. The imaging technology uses an optical shutter constructed by using the optical Kerr effect, which is generally called an optical Kerr gate, does not need phase matching, has high gating photon efficiency, and has the switching time reaching the femtosecond order. Therefore, the optical Kerr gate gating imaging technology is widely applied to the research fields of ultrafast dynamic process recording, high-time-resolution fluorescence microscopy, identification of objects in a strong scatterer and the like, and has important scientific significance and application value.
In the traditional optical Kerr gate gating imaging technology, in order to ensure higher signal transmittance, an optical Kerr medium is often required to have a nonlinear effect with higher intensity, and the origin of the nonlinear optical effect of the material often comprises a non-electronic response mechanism with large specific gravity. For example, carbon disulfide, which is the most commonly used optical kerr medium at present, has a major source of the third-order nonlinear optical effect and a molecular reorientation effect, and when the switch pulse excitation disappears, it has a longer molecular relaxation time, so that the optical kerr gate closing time using carbon disulfide as a medium is increased, and the time resolution of gated imaging is limited. On the other hand, if the optical kerr gate uses an optical kerr medium whose nonlinear response completely originates from the electronic response, such as quartz glass, the switching time is very fast and is limited mainly by the width of the switching pulse, but the optical nonlinear strength of such materials is often weak, and the formed optical kerr gate has lower signal transmittance under the same conditions. Therefore, various technologies are developed to improve the switching time and transmittance of the optical kerr gate, and the method has very important significance for the application of the optical kerr gate.
Disclosure of Invention
The invention aims to provide a method and a device for realizing a femtosecond optical Kerr gate with high transmittance, fast switching time and simple and convenient operation by double switching pulses.
In order to achieve the purpose, the invention adopts the technical scheme that:
a femtosecond double-switch optical Kerr gate based on optical birefringence effect comprises a femtosecond laser, wherein a first reflector and a beam splitting sheet are arranged on a light emitting path of the femtosecond laser, the beam splitting sheet divides the light path into a detection light path and a switch light path, and a second reflector, a first attenuation sheet, a first convex lens, a polarizer, an optical Kerr medium, an analyzer, a second convex lens, a short-pass filter, a second attenuation sheet and a detector are sequentially arranged on the detection light path, so that detection light is gated by the double-switch optical Kerr gate; the polarization direction of the polarizer is the same as that of femtosecond detection pulse light in a detection light path, the polarization direction of the analyzer is perpendicular to that of the femtosecond detection pulse light, a long-pass filter and a half-wave plate are sequentially arranged on the switch light path and used for adjusting the polarization direction of pump light, the birefringent crystal is used for generating two switch light pulses with specific time delay and mutually perpendicular polarization directions, the third attenuator reaches an optical Kerr medium through an optical delay line used for adjusting the optical path of the switch pulse, the third reflector, the fourth reflector and the third convex lens, and the spatial position of the switch pulse light incident into the optical Kerr medium is coincident with the spatial position of the femtosecond detection pulse light in the optical Kerr medium.
There is a certain time delay between the two separated switch lights, which is equivalent to two consecutive optical kerr gates. The second optical Kerr gate is approximately positioned at the closing stage of the first optical Kerr gate on the time axis, and the two optical Kerr effects in the time period generate the mutual offset effect, so that the closing speed of the optical Kerr gate is accelerated; the relative position of the two gates is determined by the thickness of the birefringent crystal, and the ratio of the switching pulse intensities of the two gates can be adjusted by the half-wave plate and the birefringent crystal.
The femtosecond laser is a femtosecond laser system with an amplifier;
the beam splitting ratio of the beam splitting sheet is 1: 1.
The first, second and third attenuation sheets are neutral attenuation sheets, and comprise neutral attenuation sheets with fixed optical density or variable neutral density attenuation sheets.
The optical delay line consists of a precision stepping moving platform controlled by a computer and two mutually perpendicular reflectors arranged on the precision stepping moving platform, and the two mutually perpendicular reflectors are used for carrying out back reflection on the femtosecond switch pulse light; the precise stepping mobile platform adjusts the optical path of the femtosecond switch pulse light, the adjustment precision is 1.5-15 micrometers, and the minimum optical path change amount of an optical delay line is 10-100 fs.
The half wave plate is a zero-order half wave plate, and is made of quartz materials or BK glass.
The polarizer and the analyzer are prism polarizers or extinction ratios of more than 1041 a thin film polarizer; wherein the prism polarizer comprises a nicol prism polarizer, a glantylor prism polarizer, or a wollaston prism polarizer.
The optical Kerr medium used is a third-order nonlinear optical material.
The optical Kerr medium is an optical Kerr medium with incomplete electronic response including carbon disulfide, nitrobenzene, carbon tetrachloride, benzene and NMP.
A method for realizing a femtosecond double-switch optical Kerr gate based on an optical birefringence effect comprises the following steps:
1) polarized femtosecond pulse laser light emitted by a femtosecond laser 1 is divided into two beams by a beam splitting sheet 3, wherein one beam is used as femtosecond detection pulse light of a detection light path, and the other beam is used as femtosecond switch pulse light of a switch light path;
2) the femtosecond detection pulse light passes through the second reflecting mirror 4, the first attenuation sheet 5, the first convex lens 6, the polarizer 7, the optical Kerr medium 8, the analyzer 9, the second convex lens 10, the short-pass filter 11 and the second attenuation sheet 12 to form the femtosecond optical Kerr gate. The polarizer 7 and the analyzer 9 are adjusted to be parallel to and perpendicular to the polarization direction of the probe light, respectively.
3) The switching light passes through a long-pass filter 14 and a half-wave plate 15, the half-wave plate 15 is used for adjusting the polarization direction of the pumping light, the birefringent crystal 16 is used for generating two switching light pulses with specific time delay and mutually perpendicular polarization directions, the third attenuator 17 passes through an optical delay line 18 for adjusting the optical path of the switching light pulses, a third reflector 19, a fourth reflector 20 and a third convex lens 21 and reaches the optical Kerr medium 8.
4) The half-wave plate 15 is adjusted so that the polarization direction of the switching light pulse before entering the birefringent crystal is changed, the initial optical axis direction of the half-wave plate 15 is 45 degrees with the horizontal direction, and the polarization direction of the pump light passing through the half-wave plate 15 is changed into vertical polarization. The half-wave plate 15 is rotated by an angle theta, the polarization direction of the pump light passing through the half-wave plate 15 is rotated by 2 theta, the birefringent crystal 16 is used to generate two switching light pulses with polarization directions perpendicular to each other with a specific time delay, and the polarization direction of the pump light incident on the birefringent crystal 16 is at an angle (45-2 theta) to the optical axis of the birefringent crystal 16. Due to the optical double refraction effect, the switching light pulse generates two intensities I after passing through the double refraction crystalgsin2(45 ° -2 θ) and Igcos2(45 ° -2 θ) switching light pulses. The intensity ratio of the two switching light pulses can be varied by rotating the half-wave plate.
5) According to the optical Kerr signal received by the detector 13, the optical delay line 18 is controlled to move by a precise stepping moving platform controlled by a computer, optical Kerr signal data are collected in real time, the intensity ratio of two switching light pulses is continuously adjusted by a half-wave plate, and an optical Kerr signal curve under the simultaneous action of the two switching light beams is obtained. The optical Kerr gate with high transmittance and ultra-fast switching time can be obtained.
Compared with the prior art, the invention has the following beneficial effects:
the femtosecond double-switch optical Kerr gate technology based on the optical birefringence effect divides an optical path into a detection optical path and a switch optical path. A long-pass filter and a half-wave plate are sequentially arranged on a switch light path, the half-wave plate is used for adjusting the polarization direction of pump light, a birefringent crystal is used for generating two switch light Pulses With specific time delay and mutually perpendicular polarization directions, fixed time delay exists between two separated switch Pulses, the time delay is 140fs, the time delay of 140fs is determined by referring to the research work of the existing Double-path Double-switch light Kerr Gate (W.Tan, J.Ma, Y.Zheng, and J.Tong, ' interferometric Optical Kerr Gate With Double-wavelength gates, ' IEEE PHOTONIC TECH L30, 266 and 269(2018) '), the polarization direction of the switch light Pulses incident in front of the birefringent crystal is changed by rotating the half-wave plate in front of the birefringent crystal, when the switch light passes through the birefringent crystal, two switches With mutually perpendicular polarization and certain time delay are generated due to the Optical birefringence effect, the intensity of the two switching light pulses depends on the polarization direction of the switching light pulse which enters the birefringent crystal, the adjustment of the intensity of the two pumping light pulses can be realized through the combination of the half-wave plate and the birefringent crystal, the optical axis direction of the birefringent crystal and the polarization direction of the detection light form 45 degrees, the third attenuation plate, the optical delay line for adjusting the optical path of the switching light, the third reflector, the fourth reflector and the third convex lens reach the optical Kerr medium, the second switching light pulse slightly lags behind the first switching light pulse on the optical path, the polarization direction of the second switching light pulse is perpendicular to the polarization direction of the first switching light pulse, and the second switching light pulse is the second optical Kerr gate which performs reverse action on medium molecules. The second optical Kerr gate is located at the closing stage of the first optical Kerr gate on the time axis, and the two optical Kerr effects in the time period generate the mutual cancellation effect, so that the closing speed of the closing stage of the optical Kerr gate is accelerated, and the switching time of the optical Kerr gate is obviously shortened under the condition of high transmittance. The detection light path is the same as that of the traditional optical Kerr gate, the optical Kerr gate is controlled to be opened and closed by double-switch pulse through the second reflecting mirror, the first attenuation sheet, the first convex lens, the polarizer, the optical Kerr medium, the analyzer, the second convex lens, the short-pass filter, the second attenuation sheet and the detector, the gating of high transmittance and high time resolution of signal light is realized, and the optical Kerr gate has important application value in the fields of femtosecond time resolution ultrafast fluorescence dynamics research and the like.
The invention provides a method for realizing high transmittance and ultrafast switching time of a femtosecond optical Kerr gate by utilizing double-switching pulses based on an optical birefringence effect, which is characterized in that the intensities of two optical Kerr gates are adjusted to achieve the following conditions: the light intensity of the second path of switch is not higher than that of the first path of switch, and a certain ratio is kept; the polarization directions of the two paths of switching light are mutually vertical and form an angle of 45 degrees with the polarization direction of the detection light; the second optical Kerr gate is slightly behind the first optical Kerr gate in the time axis and is located at the closing stage, and the delay time of the two switching pulse lights used in the present invention depends on the thickness of the birefringent crystal and is about 140 fs. In the traditional femtosecond optical Kerr gate with single switching pulse, the closing time of the optical Kerr gate is long due to the fact that the high-transmittance optical Kerr dielectric material usually has long relaxation time; the invention leads the optical Kerr gate to be effectively controlled by the second beam of switching pulse in the closing stage of the first switching pulse excitation by introducing the second switching light pulse and continuously adjusting the relative intensity of the second switching light pulse, thereby ensuring that the transmittance of the optical Kerr gate is mainly influenced by the first switching pulse, greatly shortening the closing time of the optical Kerr gate under the regulation and control of the second switching pulse, and further simultaneously realizing the high transmittance and the ultra-fast switching time of the femtosecond optical Kerr gate.
Drawings
FIG. 1 is a schematic diagram of an apparatus of a femtosecond dual-switch optical Kerr gate technology based on an optical birefringence effect provided by the invention;
FIG. 2 is a schematic diagram of a dual-open optical pulse generating module provided by the present invention;
fig. 3(a) shows the results of normalization of data using the optical kerr signal intensity curve (optical kerr medium CS2) measured by the present invention under the action of two switching pulses with different light intensity ratios, as shown in fig. 3 (b).
Fig. 4(a) and (b) are graphs comparing the normalized signal intensity curve and the peak signal transmittance (optical kerr medium CS2) measured by the femtosecond dual-switching optical kerr gate based on the optical birefringence effect according to the present invention with the normalized time-resolved optical kerr signal time-resolved curve and signal transmittance measured by the conventional optical kerr gate and quartz glass.
Wherein: the device comprises a femtosecond laser 1, a first reflector 2, a first beam splitter 3, a second reflector 4, a first attenuator 5, a polarizer 6, a first convex lens 7, an optical Kerr medium 8, a polarization analyzer 9, a second convex lens 10, a short-pass filter 11, a second attenuator 12, a detector 13, a long-pass filter 14, a half-wave plate 15, a birefringent crystal 16, a third attenuator 17, an optical delay line 18, a third reflector 19, a fourth reflector 20 and a third convex lens 21.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
The Femtosecond dual-switch Optical Kerr Gate based on the Optical birefringence effect provided by the invention takes two switch Optical Pulses With fixed time delay (140fs) and mutually vertical polarization generated by a birefringent crystal as the switch light in a traditional Optical Kerr Gate, wherein the time delay of 140fs is determined by referring to the research work of the existing dual-switch Optical Kerr Gate (W.Tan, J.Ma, Y.ZHEN, and J.Tong, femtocell Optical Kerr Gate With Double Gate Pulses, IEEE PHOTONIC TECH L30, 266 and 269 (2018)), and the Optical axis direction of the birefringent crystal is set to be 45 degrees With the polarization direction of the detection light. The polarization direction of the switch light pulse before the birefringent crystal is changed by rotating the half-wave plate in front of the birefringent crystal, when the switch light passes through the birefringent crystal, two switch light pulses which are vertical to each other in polarization and have certain time delay are generated due to an optical birefringence effect, the intensities of the two switch light pulses depend on the polarization direction of the switch light pulse before the birefringent crystal, the intensities of the two pump light pulses can be adjusted by combining the half-wave plate and the birefringent crystal, the intensities of the two switch light pulses are changed by rotating the half-wave plate, and the closing stage of the first optical Kerr gate can be effectively controlled by the second switch light.
As shown in fig. 1, the femtosecond dual-switch optical kerr gate based on the optical birefringence effect provided by the present invention includes a femtosecond laser 1, a first reflector 2 and a beam splitter 3 are arranged on a transmission optical path of the femtosecond laser 1, the beam splitter 3 divides the optical path into a detection optical path and a switch optical path, wherein the detection optical path is sequentially provided with a second reflector 4, a first attenuator 5, a first convex lens 6, a polarizer 7, an optical kerr medium 8, an analyzer 9, a second convex lens 10, a short-pass filter 11, a second attenuator 12 and a detector 13, so that the detection light is gated by the dual-switch optical kerr gate; the polarization direction of the polarizer 7 is the same as that of the femtosecond detection pulse light in the detection light path, the polarization direction of the analyzer 9 is perpendicular to that of the femtosecond detection pulse light, a long-pass filter 14 and a half-wave plate 15 are sequentially arranged on the switch light path, the half-wave plate 15 is used for adjusting the polarization direction of the pump light, the birefringent crystal 16 is used for generating two switch light pulses with specific time delay and mutually perpendicular polarization directions, the third attenuator 17, an optical delay line 18 for adjusting the optical path of the switch light pulses, a third reflector 19, a fourth reflector 20 and a third convex lens 21 reach the optical kerr medium 8, and the spatial position of the switch light pulses incident into the optical kerr medium coincides with the spatial position of the femtosecond detection pulse light in the optical kerr medium.
As shown in fig. 2, fig. 2 is a schematic diagram of a dual-polarization optical pulse generating module provided by the present invention, an initial optical axis direction of the half-wave plate 15 is 45 ° from a horizontal direction, and a polarization direction of pump light passing through the half-wave plate 15 of the horizontally polarized switch light is changed into a vertical polarization. The half-wave plate 15 is rotated by an angle theta, the polarization direction of the pump light passing through the half-wave plate 15 is rotated by 2 theta, the birefringent crystal 16 is used to generate two switching light pulses with polarization directions perpendicular to each other with a specific time delay, and the polarization direction of the pump light incident on the birefringent crystal 16 is at an angle (45-2 theta) to the optical axis of the birefringent crystal 16. Due to the optical double refraction effect, the switching light pulse generates two intensities I after passing through the double refraction crystalgsin2(45 ° -2 θ) and Igcos2(45 ° -2 θ) switching light pulses. The two switching light pulses have mutually perpendicular polarizations and have a time delay which depends on the thickness of the birefringent crystalFor 140fs, the time delay of 140fs is determined by referring to the existing research work of the two-way and two-switch Optical Kerr Gate (W.Tan, J.Ma, Y.ZHEN, and J.Tong, "femtocell Optical Kerr Gate With Double gates," IEEE PHOTONIC TECH L30, 266-269 (2018)), and the intensity ratio of two switch Optical Pulses can be changed by rotating the half-wave plate.
The femtosecond laser comprises a femtosecond laser system of an amplifier;
the beam splitting ratio of the beam splitting sheet is 1: 1.
The first, second and third attenuation sheets 5, 12 and 17 are neutral attenuation sheets, and comprise neutral attenuation sheets with fixed optical density or variable neutral density attenuation sheets.
The first optical delay line consists of a precise stepping moving platform controlled by a computer and two mutually perpendicular reflectors arranged on the precise stepping moving platform, and the two mutually perpendicular reflectors are used for carrying out back reflection on the femtosecond switch pulse light; the precise stepping mobile platform adjusts the optical path of the femtosecond switch pulse light, the adjustment precision is 1.5-15 microns, and the minimum optical path change amount of the first optical delay line and the second optical delay line is 10-100 fs.
The half wave plate is a zero-order half wave plate, and is made of quartz materials or BK glass.
The polarizer, the analyzer and the polaroid are prism polarizers or have extinction ratio more than 1041 a thin film polarizer; wherein the prism polarizer comprises a nicol prism polarizer, a glantylor prism polarizer, or a wollaston prism polarizer.
The optical Kerr medium used is a third-order nonlinear optical material.
The optical Kerr medium comprises carbon disulfide, nitrobenzene, carbon tetrachloride, benzene, NMP and other optical Kerr media with incomplete electronic response.
The device optimization parameters of the femtosecond double-switch optical Kerr gate technology based on the optical birefringence effect are as follows:
the single pulse energy of the femtosecond pulse laser emitted by the femtosecond laser is 3mJ, the pulse width is 50fs, and the repetition frequency output by the amplifier is 1 kHz; the beam splitting ratio of the beam splitting sheets is 1:1, and the light intensity of each beam is flexibly adjusted by the three attenuation sheets; focal lengths of the first, second and third convex lenses are 25cm, 20cm and 30cm, respectively; the polarizer, the analyzer and the polaroid are Nicol prism polarizers, and the aperture of the light transmission is 1.2 cm; the minimum optical path change amount of the optical delay line is 10.4 fs; carbon disulfide is used as an optical Kerr medium.
The invention provides a method for realizing high transmittance and ultrafast switching time of a femtosecond optical Kerr gate by using double switching pulses generated by an optical birefringence effect, which is characterized in that two switching light pulses are generated by a birefringence crystal, and the intensity of the two switching light pulses is adjusted by combining a half-wave plate and the birefringence crystal so as to achieve the following conditions: the light intensity of the second path of switch is not higher than that of the first path of switch; the polarization directions of the two paths of switching light are mutually vertical and form an angle of 45 degrees with the polarization direction of the detection light; the second Optical Kerr Gate lags the first one slightly in time, With a lag time determined by the thickness of the birefringent crystal of about 140fs, where the 140fs time delay is determined by reference to the existing work on the two-way, two-switch Optical Kerr Gate (W.Tan, J.Ma, Y.ZHEN, and J.Tong), "femto Optical Kerr Gate With Double Gate filters," IEEE PHOTONIC TECH L30, 266-269(2018). In the traditional femtosecond optical Kerr gate with single switching pulse, the closing time of the optical Kerr gate is long due to the fact that the high-transmittance optical Kerr dielectric material usually has long relaxation time; the invention leads the optical Kerr gate to be effectively controlled by the second beam of switch pulse in the closing stage of the first switch pulse excitation by introducing the second beam of switch pulse and continuously adjusting the relative intensity of the second beam of switch pulse, thereby ensuring that the transmittance of the optical Kerr gate is mainly influenced by the first switch pulse, greatly shortening the closing time of the optical Kerr gate under the regulation and control of the second switch pulse, and further realizing the high transmittance and the ultrafast switching time of the femtosecond optical Kerr gate.
Referring to fig. 1 and 2, the method specifically includes the following steps:
1) polarized femtosecond pulse laser light emitted by a femtosecond laser 1 is divided into two beams by a beam splitting sheet 3, wherein one beam is used as femtosecond detection pulse light of a detection light path, and the other beam is used as femtosecond switch pulse light of a switch light path;
2) the femtosecond detection pulse light passes through the second reflecting mirror 4, the first attenuation sheet 5, the first convex lens 6, the polarizer 7, the optical Kerr medium 8, the analyzer 9, the second convex lens 10, the short-pass filter 11 and is used for filtering pump light with the wavelength less than 800nm, and the second attenuation sheet 12 forms the femtosecond optical Kerr gate. Respectively adjusting the polarizer 7 and the analyzer 9 to the parallel direction and the vertical direction of the polarization direction of the detection light;
3) the switching light passes through the long-pass filter 14, and the long-pass filter 14 is used for filtering the noise of the pump light with the wavelength being more than 800 nm;
4) the switching light passes through a half-wave plate 15, the half-wave plate 15 is used for adjusting the polarization direction of the pumping light, a birefringent crystal 16, the birefringent crystal 16 is used for generating two switching light pulses with specific time delay and mutually perpendicular polarization directions, and the switching light reaches the optical Kerr medium 8 through a third attenuation plate 17, an optical delay line 18 for adjusting the optical path of the switching light pulses, a third reflector 19, a fourth reflector 20 and a third convex lens 21. The half-wave plate 15 is adjusted so that the polarization direction of the switching light pulse before entering the birefringent crystal is changed, the initial optical axis direction of the half-wave plate 15 is 45 degrees with the horizontal direction, and the polarization direction of the pump light passing through the half-wave plate 15 is changed into vertical polarization. The half-wave plate 15 is rotated by an angle theta, the polarization direction of the pump light passing through the half-wave plate 15 is rotated by 2 theta, the birefringent crystal 16 is used to generate two switching light pulses with polarization directions perpendicular to each other with a specific time delay, and the polarization direction of the pump light incident on the birefringent crystal 16 is at an angle (45-2 theta) to the optical axis of the birefringent crystal 16. Due to the optical double refraction effect, the switching light pulse generates two intensities I after passing through the double refraction crystalgsin2(45 ° -2 θ) and Igcos2(45 ° -2 θ) switching light pulses. Changing the intensity ratio of the two switching lights by rotating the half-wave plate;
5) according to the optical Kerr signal received by the detector 13, the optical delay line 18 is controlled to move by a precise stepping moving platform controlled by a computer, optical Kerr signal data are collected in real time, the intensity ratio of two switching light pulses is continuously adjusted by a half-wave plate, and an optical Kerr signal curve under the simultaneous action of the two switching light beams is obtained. The optical Kerr gate with high transmittance and ultra-fast switching time can be obtained.
Example 1
In this example, carbon disulfide is used as the optical kerr medium. Carbon disulfide was used as a reference sample. The method comprises the following specific implementation steps:
(1) the femtosecond pulse laser with single pulse energy of 3mJ, pulse width of 50fs, repetition frequency of 1kHz and horizontal polarization emitted from the femtosecond laser is divided into two beams by a beam splitting sheet with beam splitting ratio of 1:1, one beam is probe light, and the other beam is switch light.
(2) The detection light is transmitted through the second reflector to adjust the transmission direction, the intensity of the detection light is adjusted through the first attenuation sheet, the detection light is focused through the first convex lens, enters the polarizer and the optical Kerr medium carbon disulfide, then passes through the analyzer, then is changed into parallel light through the second convex lens, and finally enters the detector.
(3) The optical fiber switch comprises a switch light long-pass filter 14, a half-wave plate 15, the half-wave plate 15 is used for adjusting the polarization direction of pump light, a birefringent crystal 16, the birefringent crystal 16 is used for generating two switch light pulses with specific time delay and mutually perpendicular polarization directions, a third attenuator 17, an optical delay line 18 used for adjusting the optical path of the switch light pulses, a third reflector 19, a fourth reflector 20 and a third convex lens 21 reach an optical Kerr medium 8, and the spatial position of the switch light pulses incident into the optical Kerr medium coincides with the spatial position of femtosecond detection pulse light in the optical Kerr medium.
(4) And scanning the optical Kerr signal intensity curve in real time to finally obtain the optical Kerr signal with high transmittance and high time resolution. The relationship between the intensity ratio of different switching light pulses and the original signal intensity is shown in fig. 3(a), and it can be seen that the peak transmittance of the signal gradually decreases as the intensity of the second switching light increases. After the data is normalized, the result is shown in fig. 3(b), and it can be seen that when the intensity ratio relationship of the two switching light pulses is Ig2＝0.53Ig1The switching time can be realized to a minimum of about 142 fs.
Further, to obtain the methodComparing the obtained result with the conventional method, and after the measurement in the step (4) is finished, under the condition of optimal switching time, namely the strength ratio relation of the two switching light pulses is Ig2＝0.53Ig1Meanwhile, the peak signal transmittance is optimized by increasing the switching light intensity, the optimized result is shown in fig. 4(a) and (b), the light path is changed into a conventional optical kerr gate by moving out the birefringent crystal, the optical kerr medium is changed into carbon disulfide and fused silica, and the optical kerr signal intensity curve of the conventional optical kerr gate is measured. As shown in fig. 4(a) and (b), are graphs comparing the normalized curves and signal transmittance of a conventional optical kerr gate using fused silica and carbon disulfide as kerr media with the measurements of the device provided by the present invention.
As shown in fig. 4(a) and (b), the measured signal intensity normalization curve and the signal peak transmittance of the femtosecond dual-switch optical kerr gate based on the optical birefringence effect provided by the present invention are shown, in this measurement, the transmittance of the dual-switch optical femtosecond optical kerr gate is higher relative to that of fused silica, and the gate opening time is shorter relative to that of the conventional optical kerr gate using carbon disulfide as kerr medium.
As shown in fig. 4(a) and (b), it can be seen from the measured normalized signal intensity curves that the full width at half maximum of the conventional carbon disulfide optical kerr gate is about 415fs, the full width at half maximum of the dual-switch femtosecond optical kerr gate provided by the present invention is about 142fs, and the time resolution is significantly improved. The full width at half maximum of a solid medium such as quartz glass is also about 96fs, but the transmittance thereof is too low as shown in FIG. 4 (b).
Claims (8)
1. A femtosecond double-switch optical Kerr gate based on optical birefringence effect comprises a femtosecond laser (1), and is characterized in that: a first reflector (2) and a beam splitting sheet (3) are arranged on a light emitting path of the femtosecond laser (1), the beam splitting sheet (3) divides the light path into a detection light path and a switch light path, wherein a second reflector (4), a first attenuation sheet (5), a first convex lens (6), a polarizer (7), an optical Kerr medium (8), an analyzer (9), a second convex lens (10), a short-pass filter (11), a second attenuation sheet (12) and a detector (13) are sequentially arranged on the detection light path, so that the detection light is gated by a double-switch optical Kerr gate; the polarization direction of the polarizer (7) is the same as that of femtosecond detection pulse light in a detection light path, the polarization direction of the analyzer (9) is vertical to that of the femtosecond detection pulse light, a long-pass filter (14) and a half-wave plate (15) are sequentially arranged on the switch light path, the half-wave plate (15) is used for adjusting the polarization direction of pump light, the birefringent crystal (16) is used for generating two switch light pulses with specific time delay and mutually vertical polarization directions, the third attenuator (17), an optical delay line (18) used for adjusting the optical path of the switch pulses, a third reflector (19), a fourth reflector (20) and a third convex lens (21) reach an optical Kerr medium (8), and the space position of the switch pulse light incident into the optical Kerr medium is coincided with the space position of the femtosecond detection pulse light in the optical Kerr medium.
2. The femtosecond dual-switching optical Kerr gate based on optical birefringence effect according to claim 1, wherein: two switching pulses with fixed time delay (140fs) and mutually perpendicular polarization are generated by using a birefringent crystal (16), the optical axis direction of the birefringent crystal (16) and the polarization direction of the probe light form 45 degrees, the intensity ratio of the two switching pulse lights changes the polarization direction of the incident switching pulse light through a rotating half-wave plate (15) and is adjusted by combining the birefringent crystal.
3. The femtosecond dual-switching optical Kerr gate based on optical birefringence effect according to claim 1 or 2, characterized in that:
the femtosecond laser (1) is a femtosecond laser system with an amplifier;
the beam splitting ratio of the beam splitting sheet (3) is 1: 1;
the first, second and third attenuation sheets (5), (12) and (17) are neutral attenuation sheets, and comprise neutral attenuation sheets with fixed optical density or variable neutral density attenuation sheets;
the half wave plate (15) is a zero-order half wave plate, and is made of quartz materials or BK glass.
4. The femtosecond dual-switching optical Kerr gate based on optical birefringence effect according to claim 1, wherein: the optical delay line (18) consists of a precision stepping moving platform controlled by a computer and two mutually perpendicular reflectors arranged on the precision stepping moving platform, and the two mutually perpendicular reflectors are used for carrying out back reflection on the femtosecond switch pulse light; the precise stepping mobile platform adjusts the optical path of the femtosecond switch pulse light, the adjustment precision is 1.5-15 microns, and the minimum optical path change quantity of the optical delay line (18) is 10-100 fs.
5. The femtosecond dual-switching optical Kerr gate based on optical birefringence effect according to claim 1, wherein: the polarizer (7) and the analyzer (9) are prism polarizers or have extinction ratio larger than 1041 a thin film polarizer; wherein the prism polarizer comprises a nicol prism polarizer, a glantylor prism polarizer, or a wollaston prism polarizer.
6. The femtosecond dual-switching optical Kerr gate based on optical birefringence effect as recited in claim 1, wherein: the optical Kerr medium (8) used is a third-order nonlinear optical material.
7. The femtosecond dual-switching optical Kerr gate based on optical birefringence effect according to claim 1 or 7, wherein: the optical Kerr medium comprises carbon disulfide, nitrobenzene, carbon tetrachloride, benzene and NMP incompletely electronically-responsive optical Kerr medium.
8. A method for implementing a femtosecond dual-switch optical kerr gate based on an optical birefringence effect as defined in claim 1, comprising the following steps:
1) polarized femtosecond pulse laser light emitted by a femtosecond laser (1) is divided into two beams by a beam splitting sheet (3), wherein one beam is used as detection pulse light, and the other beam is used as switch pulse light;
2) the detection pulse light passes through the second reflecting mirror (4), the first attenuation sheet (5), the first convex lens (6), the polarizer (7), the optical Kerr medium (8), the analyzer (9), the second convex lens (10), the short-pass filter (11), the second attenuation sheet (12) and the detector (13), so that the detection light is gated by the double-switch optical Kerr gate; the polarization direction of the polarizer (7) is the same as that of the femtosecond detection pulse light in the detection light path, and the polarization direction of the analyzer (9) is vertical to that of the femtosecond detection pulse light;
3) the optical path of the switching pulse light is adjusted through an optical delay line (18);
4) the switching pulse light passes through a long-pass filter (14) and a half-wave plate (15), the half-wave plate (15) is used for adjusting the polarization direction of the pumping light, the birefringent crystal (16) is used for generating two switching light pulses with specific time delay and mutually perpendicular polarization directions, the third attenuator (17), an optical delay line (18) used for adjusting the optical path of the switching pulse, a third reflector (19), a fourth reflector (20) and a third convex lens (21) reach the optical Kerr medium (8), and the spatial position of the switching pulse light incident into the Kerr medium coincides with the spatial position of the femtosecond detection pulse light in the optical Kerr medium;
5) according to the optical Kerr signal received by the detector (13), the optical delay line (18) is controlled to move by a precise stepping moving platform controlled by a computer and optical Kerr signal data is collected in real time, a time-resolved optical Kerr signal curve under the simultaneous action of two switching pulses is obtained, and the optical Kerr gate with high transmittance and ultra-fast switching time can be obtained.
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| CN106647096A (en) * | 2017-02-21 | 2017-05-10 | 西安交通大学 | Double-switching-pulse type femtosecond optical Kerr-gate and implementation method thereof |
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| JP2003194719A (en) * | 2001-12-25 | 2003-07-09 | Yokohama Tlo Co Ltd | Method and apparatus for real-time imaging spectrometry |
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