CN110687093A - Double-frequency CARS measuring device and method based on bound-state optical solitons - Google Patents
Double-frequency CARS measuring device and method based on bound-state optical solitons Download PDFInfo
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- CN110687093A CN110687093A CN201910914147.4A CN201910914147A CN110687093A CN 110687093 A CN110687093 A CN 110687093A CN 201910914147 A CN201910914147 A CN 201910914147A CN 110687093 A CN110687093 A CN 110687093A
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
- G01N21/65—Raman scattering
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/01—Arrangements or apparatus for facilitating the optical investigation
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- G—PHYSICS
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- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/264—Optical coupling means with optical elements between opposed fibre ends which perform a function other than beam splitting
- G02B6/266—Optical coupling means with optical elements between opposed fibre ends which perform a function other than beam splitting the optical element being an attenuator
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/27—Optical coupling means with polarisation selective and adjusting means
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/01—Arrangements or apparatus for facilitating the optical investigation
- G01N2021/0106—General arrangement of respective parts
- G01N2021/0112—Apparatus in one mechanical, optical or electronic block
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
- G01N21/65—Raman scattering
- G01N2021/653—Coherent methods [CARS]
Abstract
The invention discloses a dual-frequency CARS measuring device and method based on bound-state optical solitons, wherein the device at least comprises a femtosecond laser (1), an ultrashort pulse beam splitting adjusting part, a Stokes optical pulse generating and transmitting optical path, a pumping light transmitting optical path, a beam combining mirror (15) and a CARS microscopic imaging system (16) which are sequentially connected; based on soliton self-frequency shift effect and birefringence effect when ultrashort pulse is transmitted in high nonlinear photonic crystal fiber, bound state optical solitons with time domain overlapping and wavelength separation are generated. When the bound state optical soliton is used as a Stokes light pulse of the CARS system, the bound state optical soliton can simultaneously act with a pumping light pulse to simultaneously excite and detect the resonance frequencies of two molecules to be detected. The invention simplifies the system structure of the traditional CARS measurement system, reduces the system cost, and improves the chemo-selective imaging capability and the simultaneous multi-molecule detection capability of the CARS system.
Description
Technical Field
The invention belongs to the field of nonlinear optics, soliton and coherent Raman spectrum detection, and particularly relates to a double-frequency CARS measuring device and method.
Background
Coherent anti-Stokes Raman scattering (CARS) technology has wide application in the fields of cell life science and the like due to its specific chemoselective detection capability. In the CARS technology, a pumping light pulse and a Stokes light pulse are simultaneously incident into a sample to be detected, the frequency difference of the two incident pulses is adjusted to be the same as the resonance frequency of a molecule to be detected, so that resonance excitation is realized, an anti-Stokes Raman scattering signal is generated, and chemoselective imaging of the sample to be detected can be realized by detecting the intensity and distribution of the anti-Stokes signal. The multichannel CARS technology can simultaneously measure a plurality of Raman scattering spectral lines, so that the influence of the overlapping of Raman resonance spectral bands on the chemical selectivity detection of a sample to be detected can be overcome, and the selective detection capability of molecules to be detected is improved; in addition, the multi-path CARS technology can simultaneously realize simultaneous observation of multiple molecular resonances, which is helpful for further revealing the interaction mechanism between cells in cell life activities, and thus, the multi-path CARS technology is receiving more and more attention. The multi-path CARS technique doubles the system complexity and system cost by requiring multiple incident pulse pairs of different wavelengths. The wavelength tuning method based on the soliton self-frequency shift effect of the high-nonlinearity photonic crystal fiber is widely applied to the CARS system due to the fact that the structure is simple, and the wavelength can be tuned continuously in a large range.
Disclosure of Invention
The invention aims to provide a double-frequency CARS measuring device and method based on bound-state optical solitons, which can simplify the requirements on an excitation light source while keeping the advantages of a multi-path CARS technology, can generate a beam of pumping light and two beams of Stokes light pulses with different wavelengths by using only one ultrashort pulse laser and one high nonlinear photonic crystal fiber, and improve the chemical selectivity imaging capability and the simultaneous multi-molecule detection capability of a CARS system.
A dual-frequency CARS measuring device based on bound-state optical solitons at least comprises a femtosecond laser 1, an ultrashort pulse beam splitting adjusting part, a Stokes light pulse generating and transmitting light path, a pumping light transmitting light path, a beam combining mirror 15 and a CARS microscopic imaging system 16 which are sequentially connected, wherein the femtosecond laser 1 outputs ultrashort pulses with the pulse width of 40-200 fs and linear polarization;
the ultrashort pulse beam splitting adjusting part consists of an electric control liquid crystal wave plate 2 and a polarization beam splitting prism 3 which are connected in sequence; the Stokes light pulse generating and transmitting optical path consists of a half wave plate 4, a beam expander 5, an optical fiber coupling mirror 6, a high nonlinear polarization-maintaining photonic crystal optical fiber 7, an optical fiber collimation beam expander 8, a first reflector 9 and first dispersion glass 10 which are sequentially connected; the pump light transmission optical path consists of a second reflector 11, an adjustable space light delay line 12, an adjustable attenuation sheet 13 and second dispersive glass 14 which are connected in sequence;
the output end of the polarization beam splitter prism 3 is connected with the input end of the half-wave plate 4, the output ends of the first dispersive glass 10 and the second dispersive glass 14 are respectively connected with the input end of the beam combiner 15, and the output end of the beam combiner 15 is connected with the input end of the CARS microscopic imaging system 16;
wherein:
the femtosecond laser 1 outputs an ultra-short pulse with the pulse width of 40-200 fs and linear polarization, and the ultra-short pulse is incident to the ultra-short pulse beam splitting adjusting part;
the electric control liquid crystal wave plate 2 realizes the change of the polarization state of output light;
the polarization beam splitter prism 3 is used for dividing the polarization state variable ultrashort pulse output by the electric control liquid crystal wave plate into a horizontal line polarization ultrashort pulse output by transmission and a vertical line polarization ultrashort pulse output by reflection;
the half wave plate 4 is used for adjusting the linear polarization direction of the ultrashort pulse entering the high nonlinear polarization-maintaining photonic crystal fiber 7;
the beam expander 5 is used for expanding the diameter of the light beam;
the optical fiber coupling mirror 6 is used for coupling the ultra-short pulse transmitted in the space into the high nonlinear polarization-maintaining photonic crystal fiber 7;
the high nonlinear polarization maintaining photonic crystal fiber 7 is used for generating a bound state optical soliton with time domain overlapping and spectrum wavelength difference and used as a Stokes light pulse of a dual-frequency CARS system;
the first dispersion glass 10 is used for widening Stokes light pulses and enabling the Stokes light pulses to generate linear chirp;
the adjustable space light delay line 12 is used for adjusting the delay amount of a pumping light path to ensure that pumping light pulses and Stokes light pulses are overlapped in time at a sample to be detected;
the adjustable attenuation sheet 13 is used for adjusting the optical power of the pump light pulse, so that the pump light power at the position of the sample to be detected is approximately twice of the Stokes light power, and an anti-Stokes Raman scattering signal is generated;
the second dispersive glass 14 is used for widening the pump light pulse and enabling the pump light pulse to generate linear chirp;
and the beam combining mirror 15 is used for combining and outputting the pump light pulse and the Stokes light pulse.
The CARS microscopic imaging system 16 is configured to focus the combined pump light pulse and stokes light pulse into a sample to be detected to excite a coherent anti-stokes raman scattering signal, that is, a CARS signal, and to perform collection, detection and analysis on the generated CARS signal.
The adjustable spatial light delay line 12 is composed of two right- angle reflecting prisms 121 and 122 and a high-precision electronic control displacement stage 123, wherein the second right-angle reflecting mirror 122 is fixedly arranged on the high-precision electronic control displacement stage 123, an incident ultrashort pulse is reflected to the second right-angle reflecting mirror 122 fixed on the high-precision electronic control displacement stage 123 by the first right-angle reflecting prism 121, and the ultrashort pulse reflected by the second right-angle reflecting prism 122 is reflected and output by the other right-angle side, and the high-precision electronic control displacement stage 123 is used for changing the time delay of a pumping light path and ensuring the time overlap of the pumping light pulse and the stokes light pulse.
The invention discloses a double-frequency CARS (coherent anti-interference Signal-associated-System) measuring method based on bound-state optical solitons, which comprises the following steps of:
step 1: the femtosecond laser outputs ultra-short pulse with pulse width of 40-200 fs and linear polarization to be incident to the electric control liquid crystal wave plate;
step 2: when the voltage applied by the electric control liquid crystal wave plate changes, the light power of the horizontal ultrashort pulse output by the reflection and transmission of the polarization beam splitter prism changes along with the voltage; the ultrashort pulse output by reflection of the polarization beam splitter prism is used as a pump light pulse of the dual-frequency CARS system, and the ultrashort pulse output by transmission is used for generating a bound-state light soliton and is used as a Stokes light pulse of the dual-frequency CARS system;
and step 3: the ultra-short pulse with adjustable light power transmitted and output by the polarization beam splitter prism sequentially enters the high nonlinear polarization-maintaining photonic crystal fiber through the half wave plate, the beam expander and the fiber coupling mirror, and the linear polarization direction of the ultra-short pulse entering the high nonlinear polarization-maintaining photonic crystal fiber is adjusted by the half wave plate, so that when the ultra-short pulse is incident along a certain specific direction, bound state light solitons are generated at the output end of the high nonlinear polarization-maintaining photonic crystal fiber; expanding the diameter of the ultra-short pulse light beam transmitted in space by using a beam expander to improve the coupling efficiency of the optical fiber coupling mirror; coupling the ultra-short pulse transmitted in space into the high nonlinear polarization-maintaining photonic crystal fiber by using a fiber coupling mirror; generating bound state optical solitons with the wavelength changing along with the incident ultrashort pulse optical power by utilizing the high nonlinear polarization maintaining photonic crystal fiber, and using the bound state optical solitons as Stokes optical pulses of a dual-frequency CARS system;
and 4, step 4: adjusting a half wave plate to enable the power component of the ultrashort pulse in the fast axis direction to be larger than that in the slow axis direction, so that the optical solitons generated in the fast axis direction have longer wavelength and the optical solitons generated in the slow axis direction have shorter wavelength; when the wavelengths of the optical solitons transmitted along the fast axis and the slow axis are both positioned in the anomalous dispersion region of the high nonlinear polarization-maintaining photonic crystal fiber, in the transmission process of the same section of high nonlinear polarization-maintaining photonic crystal fiber, the time required by the fast axis optical solitons with longer wavelengths is longer than that of the slow axis optical solitons with shorter wavelengths; when the fast/slow axis optical solitons with wavelength difference are transmitted in the high nonlinear polarization-maintaining photonic crystal fiber, the proper polarization direction of ultrashort pulse entering the high nonlinear polarization-maintaining photonic crystal fiber is adjusted, so that the time difference caused by the dispersion effect and the time difference caused by the birefringence effect are mutually compensated, and the fast axis solitons and the slow axis solitons at the output end of the high nonlinear polarization-maintaining photonic crystal fiber are mutually overlapped in the time domain to have certain wavelength difference on a spectrum, thereby generating bound state optical solitons;
and 5: bound state light solitons output by the high nonlinear polarization maintaining photonic crystal fiber are converted into light beams transmitted in space through a fiber collimation beam expanding lens and are used as Stokes light pulses of a dual-frequency CARS system; the Stokes light beams output by the fiber collimation beam expander are reflected and output by the beam combiner after being transmitted by the first reflector and the first dispersion glass, and the first dispersion glass is used for broadening Stokes light pulses and enabling the Stokes light pulses to generate linear chirp;
step 6: ultrashort pulses output by reflection of the polarization beam splitter prism are used as pumping light pulses of the dual-frequency CARS system, and are transmitted and output by the beam combiner after being sequentially transmitted by the second reflecting mirror, the adjustable space light delay line, the adjustable attenuation sheet and the second dispersive glass; adjusting the time delay of the pump light pulse by using an adjustable space light delay line to ensure that the pump light pulse and the Stokes light pulse are overlapped in time at the position of the sample to be detected; the optical power of the pump light pulse is adjusted by using the adjustable attenuation sheet, so that the optical power of the pump light pulse is approximately twice of the Stokes light pulse power, and the pump light pulse and the Stokes light pulse completely act to generate an anti-Stokes Raman scattering signal; broadening the pump light pulse by using a second dispersive glass and enabling the pump light pulse to generate linear chirp; selecting proper lengths of the first dispersive glass and the second dispersive glass to enable the Stokes light pulse and the pump light pulse to have the same linear chirp so as to realize spectral focusing;
and 7: the CARS microscopic imaging system can focus and emit the combined pumping light pulse and Stokes light pulse into a sample to be detected to excite an anti-Stokes Raman scattering signal, namely a CARS signal, collect the CARS signal generated by the sample to be detected to analyze the spectral components of the sample to be detected so as to realize chemoselective imaging, and realize the spatial distribution microscopic measurement of target molecules in the sample to be detected by changing the relative positions of a focusing light spot and the sample to be detected.
Compared with the traditional CARS measuring system, the double-frequency CARS measuring device and method based on the bound-state optical solitons have the following technical advantages:
1) the system is used for generating bound state optical solitons based on the high nonlinear polarization maintaining photonic crystal fiber to serve as Stokes light pulses of a dual-frequency CARS system, is simple in structure, large in wavelength tuning range, capable of continuously and rapidly adjusting wavelength, and has an essential time synchronization characteristic with pump light pulses; 2) the bound state optical solitons with two different wavelengths are used as Stokes light pulses, so that excitation and detection of two Raman resonance spectral lines can be realized simultaneously, more accurate chemical selectivity detection can be realized through the two Raman resonance spectral lines, and the influence of Raman resonance spectral overlapping on accurate positioning of molecules to be detected is reduced; 3) the dual-frequency CARS system based on the bound optical solitons can realize simultaneous measurement of two Raman resonance spectral lines, so that two different molecules to be detected can be measured simultaneously, the interaction between the two different molecules to be detected can be observed, and the essence of cell life activity can be revealed.
Drawings
FIG. 1 is a schematic diagram of a dual-frequency CARS measurement device based on bound-state optical solitons according to the present invention;
FIG. 2 is a schematic diagram of bound state optical soliton time domain and spectrum;
FIG. 3 is a schematic diagram of electric field decomposition in the fast and slow axes of an ultrashort pulse incident on a photonic crystal fiber,
wherein: e0Electric field representing incident linearly polarized ultrashort pulse, in the figure: eslowRepresenting the resolved electric field of the incident ultrashort pulse electric field in the direction of the slow axis, EfastThe method is characterized in that the method represents the decomposition electric field of an incident ultrashort pulse electric field in the fast axis direction, and theta represents the included angle between the linear polarization direction of the incident ultrashort pulse and the fast axis direction of the high nonlinear polarization-maintaining photonic crystal fiber.
Reference numerals:
1. the device comprises a femtosecond laser, 2, an electric control liquid crystal wave plate, 3, a polarization beam splitter prism, 4, a half wave plate, 5, a beam expander, 6, an optical fiber coupling mirror, 7, a high nonlinear polarization-maintaining photonic crystal optical fiber, 8, an optical fiber collimation beam expander, 9, a first reflector, 10, first dispersion glass, 11, a second reflector, 12, an adjustable space optical delay line, 13, an adjustable attenuator, 14, second dispersion glass, 15, a beam combiner, 16, a CARS microscopic imaging system, 121, a first right-angle reflecting prism, 122, a second right-angle reflecting prism, 123 and a high-precision electric control displacement platform.
Detailed Description
The technical solution of the present invention is described in detail below with reference to the accompanying drawings and examples. .
Fig. 1 is a schematic diagram of a dual-frequency CARS measurement device based on bound-state optical solitons according to the present invention. The device mainly comprises a femtosecond laser 1, an ultrashort pulse beam splitting adjusting part (consisting of an electric control liquid crystal wave plate 2 and a polarization beam splitter prism 3), a Stokes light pulse generating and transmitting light path (consisting of a half wave plate 4, a beam expander 5, an optical fiber coupling mirror 6, a high nonlinear polarization-maintaining photonic crystal fiber 7, an optical fiber collimation beam expander 8, a first reflector 9 and first dispersion glass 10), a pumping light transmitting light path (consisting of a second reflector 11, an adjustable space light delay line 12, an adjustable attenuation sheet 13 and second dispersion glass 14), a beam combiner 15 and a CARS microscopic imaging system 16.
The femtosecond laser 1 outputs the ultra-short pulse with the pulse width of 40-200 fs and linear polarization, and the ultra-short pulse is incident to the ultra-short pulse beam splitting adjusting part.
In the ultra-short pulse beam splitting adjusting part: the linear polarization ultrashort pulse is incident to the polarization beam splitter prism 3 through the electric control liquid crystal wave plate 2. The ultrashort pulse transmitted and output by the polarization beam splitter prism 3 is incident to a Stokes light pulse generation and transmission light path; the ultrashort pulse reflected and output by the polarization beam splitter prism 3 is incident to the pump light transmission optical path.
In the stokes light pulse generation and transmission optical path: the ultrashort pulse transmitted and output by the polarization beam splitter prism 3 sequentially passes through a half-wave plate 4, a beam expander 5 and a fiber coupling mirror 6 to enter a high nonlinear polarization-maintaining photonic crystal fiber 7. The stokes light beam output by the high nonlinear polarization maintaining photonic crystal 7 is incident to the first reflecting mirror 9 through the optical fiber collimation beam expanding lens 8, and the stokes light beam output by the first reflecting mirror 9 is incident to the beam combining lens 15 after passing through the first dispersion glass 10.
In the pump light transmission optical path: the ultrashort pulse reflected and output by the polarization beam splitter prism 3 is incident to the adjustable spatial light delay line 12 through the second reflecting mirror 11. The adjustable spatial light delay line 12 is composed of two right- angle reflecting prisms 121 and 122 and a high-precision electronic control displacement stage 123, the first right-angle reflecting prism 121 reflects an incident ultrashort pulse to the second right-angle reflecting mirror 122 fixed on the high-precision electronic control displacement stage 123, the ultrashort pulse reflected by the second right-angle reflecting prism 122 is reflected and output through the other right-angle side, and the high-precision electronic control displacement stage 123 is used for changing the time delay of a pumping light path and ensuring the time overlapping of the pumping light pulse and the stokes light pulse. The ultrashort pulse output by the adjustable spatial light delay line 12 is incident to the beam combiner 15 through the adjustable attenuator 13 and the second dispersive glass 14.
The beam combining mirror 15 reflects and outputs the stokes light pulses, and transmits and outputs the pump light pulses, so that beam combination of the pump light pulses and the stokes light pulses is realized. The combined pump light pulse and stokes light pulse output by the beam combining mirror 15 are incident to the CARS microscopic imaging system 16 to excite and collect the CARS signal of the sample to be detected, so that the chemical selective imaging analysis of the sample to be detected is realized.
Wherein:
the electric control liquid crystal wave plate 2 can be controlled by external voltage to realize the change of the polarization state of the output light.
The polarization beam splitter prism 3 is used for dividing the polarization state variable ultrashort pulse output by the electric control liquid crystal wave plate into a horizontal line polarization ultrashort pulse output by transmission and a vertical line polarization ultrashort pulse output by reflection.
And the half wave plate 4 is used for adjusting the linear polarization direction of the ultrashort pulse entering the high nonlinear polarization-maintaining photonic crystal fiber 7.
The beam expander 5 is used for expanding the diameter of the light beam and improving the coupling efficiency of the space light which is coupled to the high nonlinear polarization-maintaining photonic crystal fiber 7 through the optical fiber coupling mirror 6.
And the optical fiber coupling mirror 6 is used for coupling the ultra-short pulse transmitted in the space into the high nonlinear polarization-maintaining photonic crystal fiber 7.
The high nonlinear polarization-maintaining photonic crystal fiber 7 is used for generating a bound state optical soliton with time domain overlapping and spectrum wavelength difference and is used as a Stokes optical pulse of a dual-frequency CARS system.
The first dispersive glass 10 is used for widening Stokes light pulses and enabling the Stokes light pulses to generate linear chirp.
The adjustable spatial light delay line 12 is used for adjusting the delay amount of the pumping light path, so that the pumping light pulse and the stokes light pulse are overlapped in time at the sample to be measured.
The adjustable attenuation sheet 13 is used for adjusting the optical power of the pump light pulse, so that the pump light power at the position of the sample to be detected is approximately twice of the Stokes light power, and the pump light pulse and the Stokes light pulse can completely act to generate an anti-Stokes Raman scattering signal.
The second dispersive glass 14 is used for widening the pump light pulse and enabling the pump light pulse to generate linear chirp, and the length of the first dispersive glass 10 and the length of the second dispersive glass 14 are selected to enable the Stokes light pulse and the pump light pulse to have the same linear chirp, so that the high spectral resolution of the CARS signal is achieved.
And the beam combining mirror 15 is used for combining and outputting the pump light pulse and the Stokes light pulse.
The CARS microscopic imaging system 16 is used for focusing the combined pumping light pulse and Stokes light pulse into a sample to be detected to excite a coherent anti-Stokes Raman scattering signal, namely a CARS signal, and simultaneously collecting, detecting and analyzing the generated CARS signal, wherein the relative positions of the focusing light spots of the pumping light pulse and the Stokes light pulse in the sample to be detected and the sample to be detected can be changed, and the chemical selective microscopic imaging of the sample to be detected can be realized by measuring the intensity and distribution of the CARS signal at different positions of the sample to be detected.
The invention discloses a double-frequency CARS (coherent anti-interference Signal-associated-System) measuring method based on bound-state optical solitons, which mainly comprises the following steps of:
step 1: the femtosecond laser outputs ultrashort pulses with the pulse width of 40-200 fs and linear polarization to be incident to the electric control liquid crystal wave plate.
Step 2: the polarization state of the ultra-short pulse transmitted and output by the electric control liquid crystal wave plate is influenced by the voltage applied by the electric control liquid crystal wave plate and can be continuously changed among horizontal linear polarized light, elliptical polarized light, circular polarized light and vertical linear polarized light. Therefore, when the voltage applied by the electric control liquid crystal wave plate is changed, the light power of the horizontal ultrashort pulse output by the reflection and transmission of the polarization beam splitting prism is changed. The ultrashort pulse output by reflection of the polarization beam splitter prism is used as a pump light pulse of the dual-frequency CARS system, and the ultrashort pulse output by transmission is used for generating a bound-state light soliton and is used as a Stokes light pulse of the dual-frequency CARS system.
And step 3: the ultra-short pulse with adjustable light power transmitted and output by the polarization beam splitter prism sequentially enters the high-nonlinearity polarization-maintaining photonic crystal fiber through the half-wave plate, the beam expander and the fiber coupling mirror. Wherein, the half-wave plate is used for adjusting the linear polarization direction of the ultrashort pulse entering the high nonlinear polarization-maintaining photonic crystal fiber, so that when the ultrashort pulse enters the high nonlinear polarization-maintaining photonic crystal fiber along a certain specific direction, a bound state optical soliton (as shown in fig. 2) can be generated at the output end of the high nonlinear polarization-maintaining photonic crystal fiber; the beam expander is used for expanding the diameter of the ultra-short pulse light beam transmitted in space so as to improve the coupling efficiency of the optical fiber coupling mirror and further improve the utilization efficiency of the ultra-short pulse light power; the fiber coupling mirror is used for coupling the ultra-short pulse transmitted in the space into the high nonlinear polarization-maintaining photonic crystal fiber; the high nonlinear polarization-maintaining photonic crystal fiber is used for generating bound state optical solitons with the wavelength changing along with the power of incident ultrashort pulse light and is used as Stokes light pulses of a dual-frequency CARS system.
And 4, step 4: the generation process of the bound-state optical solitons is as follows: the fast axis and the slow axis of the high nonlinear polarization-maintaining photonic crystal fiber have different effective refractive indexes, so that the ultrashort pulses have different transmission speeds in the directions of the fast axis and the slow axis when being transmitted in the high nonlinear polarization-maintaining photonic crystal fiber. Therefore, when passing through the same section of high nonlinear polarization maintaining photonic crystal fiber, the transmission time required for the ultra-short pulse transmitted along the fast axis is different from that required for the ultra-short pulse transmitted along the slow axis. Since the effective refractive index of the fast axis is smaller than that of the slow axis, the transmission time of the ultra-short pulse in the fast axis direction is shorter than that of the ultra-short pulse in the slow axis direction. Due to the influence of soliton self-frequency shift effect, when the ultrashort pulse is transmitted in the high nonlinear polarization-maintaining photonic crystal fiber, soliton evolution in the fast axis direction and soliton evolution in the slow axis direction are carried out simultaneously, and the mutual influence between the fast axis direction and the slow axis direction is small. The half wave plate is adjusted to make the power component of the ultrashort pulse in the fast axis direction larger than that in the slow axis direction (as shown in fig. 3), so that the optical soliton generated in the fast axis direction has a longer wavelength and the optical soliton generated in the slow axis direction has a shorter wavelength. Due to the influence of the dispersion effect, when the wavelengths of the optical solitons transmitted along the fast axis and the slow axis are both positioned in the anomalous dispersion region of the high nonlinear polarization-maintaining photonic crystal fiber, in the process of transmitting in the same section of high nonlinear polarization-maintaining photonic crystal fiber, the time required by the fast axis optical solitons with longer wavelengths is longer than that of the slow axis optical solitons with shorter wavelengths. When fast and slow axis optical solitons with wavelength difference are transmitted in the high nonlinear polarization-maintaining photonic crystal fiber, the polarization direction of ultrashort pulse lines entering the high nonlinear polarization-maintaining photonic crystal fiber is adjusted properly, so that time difference caused by dispersion effect and time difference caused by birefringence effect can be compensated mutually, and thus the fast axis solitons and the slow axis solitons at the output end of the high nonlinear polarization-maintaining photonic crystal fiber are overlapped in time domain and have certain wavelength difference on a spectrum, as shown in fig. 2, such optical soliton pulses are bound state optical solitons.
And 5: bound light solitons output by the high nonlinear polarization-maintaining photonic crystal fiber are converted into light beams transmitted in space through the fiber collimation beam expanding lens and are used as Stokes light pulses of the dual-frequency CARS system. The first reflector of the Stokes light beam output by the fiber collimation beam expander and the first dispersive glass are reflected and output by the beam combiner after being transmitted. Wherein the first dispersive glass is configured to broaden and linearly chirp the stokes light pulses.
Step 6: ultrashort pulses output by reflection of the polarization beam splitter prism are used as pumping light pulses of the dual-frequency CARS system, and are transmitted and output by the beam combiner after being sequentially transmitted by the second reflecting mirror, the adjustable space light delay line, the adjustable attenuation sheet and the second dispersive glass. The adjustable space light delay line is used for adjusting the time delay of the pump light pulse, so that the pump light pulse and the Stokes light pulse are overlapped in time at a sample to be detected; the adjustable attenuation sheet is used for adjusting the optical power of the pump optical pulse, so that the optical power of the pump optical pulse is approximately twice of the Stokes optical pulse power, and the pump optical pulse and the Stokes optical pulse completely act to generate an anti-Stokes Raman scattering signal; the second dispersive glass serves to broaden and linearly chirp the pump light pulses. The lengths of the first dispersive glass and the second dispersive glass are selected to enable the Stokes light pulse and the pumping light pulse to have the same linear chirp, so that spectral focusing is achieved, and the spectral resolution capability of the CARS signal is improved.
And 7: and pumping light pulses and Stokes light pulses are combined by a beam combining mirror and output and then are incident to the CARS microscopic imaging system. The CARS microscopic imaging system can focus and emit the combined pumping light pulse and Stokes light pulse into a sample to be detected to excite an anti-Stokes Raman scattering signal, namely a CARS signal, collect the CARS signal generated by the sample to be detected simultaneously to analyze the spectral components of the CARS signal so as to realize chemical selective imaging, and can realize the spatial distribution microscopic measurement of target molecules in the sample to be detected by changing the relative position of a focusing light spot and the sample to be detected.
Claims (3)
1. A dual-frequency CARS measuring device based on bound-state optical solitons is characterized by at least comprising a femtosecond laser (1), an ultrashort pulse beam splitting adjusting part, a Stokes light pulse generating and transmitting light path, a pumping light transmitting light path, a beam combining mirror (15) and a CARS microscopic imaging system (16) which are connected in sequence;
the ultrashort pulse beam splitting adjusting part consists of an electric control liquid crystal wave plate (2) and a polarization beam splitting prism (3) which are connected in sequence; the Stokes light pulse generating and transmitting optical path consists of a half wave plate (4), a beam expander (5), an optical fiber coupling mirror (6), a high nonlinear polarization-maintaining photonic crystal optical fiber (7), an optical fiber collimating and beam expanding mirror (8), a first reflector (9) and first dispersion glass (10) which are sequentially connected; the pump light transmission optical path consists of a second reflector (11), an adjustable space light delay line (12), an adjustable attenuation sheet (13) and second dispersive glass (14) which are connected in sequence;
the output end of the polarization beam splitter prism (3) is connected with the input end of the half wave plate (4), the output ends of the first dispersive glass (10) and the second dispersive glass (14) are respectively connected with the input end of the beam combiner (15), and the output end of the beam combiner (15) is connected with the input end of the CARS microscopic imaging system (16);
wherein:
the femtosecond laser (1) outputs ultra-short pulse with pulse width of 40-200 fs and linear polarization, and the ultra-short pulse is incident to the ultra-short pulse beam splitting adjusting part;
the electric control liquid crystal wave plate (2) realizes the change of the polarization state of the output light;
the polarization beam splitter prism (3) is used for dividing the polarization state variable ultrashort pulse output by the electric control liquid crystal wave plate into a horizontal line polarization ultrashort pulse output by transmission and a vertical line polarization ultrashort pulse output by reflection;
the half wave plate (4) is used for adjusting the linear polarization direction of the ultrashort pulse entering the high nonlinear polarization-maintaining photonic crystal fiber (7);
the beam expanding lens (5) is used for expanding the diameter of the light beam;
the optical fiber coupling mirror (6) is used for coupling the ultra-short pulse transmitted in the space into the high nonlinear polarization-maintaining photonic crystal fiber (7);
the high nonlinear polarization-maintaining photonic crystal fiber (7) is used for generating a bound state optical soliton with time domain overlapping and spectrum wavelength difference and used as a Stokes optical pulse of a dual-frequency CARS system;
the first dispersive glass (10) is used for widening Stokes light pulses and enabling the Stokes light pulses to generate linear chirp;
the adjustable space light delay line (12) is used for adjusting the delay amount of a pumping light path to ensure that the pumping light pulse and the Stokes light pulse are overlapped in time at a sample to be detected;
the adjustable attenuation sheet (13) is used for adjusting the optical power of the pump light pulse, so that the pump light power at the position of the sample to be detected is approximately twice of the Stokes light power, and an anti-Stokes Raman scattering signal is generated;
the second dispersive glass (14) is used for widening the pump light pulse and enabling the pump light pulse to generate linear chirp;
and the beam combining mirror (15) is used for combining and outputting the pump light pulse and the Stokes light pulse.
The CARS microscopic imaging system (16) is used for focusing the combined pumping light pulse and Stokes light pulse into a sample to be detected to excite a coherent anti-Stokes Raman scattering signal, namely a CARS signal, and meanwhile, collecting, detecting and analyzing the generated CARS signal.
2. The dual-frequency CARS measuring device based on the bound-state light solitons as claimed in claim 1, wherein the tunable spatial light delay line (12) is composed of two right-angle reflecting prisms (121) (122) and a high-precision electrically-controlled displacement stage (123), wherein the second right-angle reflecting mirror (122) is fixedly disposed on the high-precision electrically-controlled displacement stage (123), the incident ultrashort pulse is reflected by the first right-angle reflecting prism (121) to the second right-angle reflecting mirror (122) fixed on the high-precision electrically-controlled displacement stage (123), and the ultrashort pulse reflected by the second right-angle reflecting prism (122) is reflected and output through the other right-angle side thereof, and the high-precision electrically-controlled displacement stage (123) is configured to change a time delay of a pumping light path and ensure a time overlap between the pumping light pulse and the Stokes light pulse.
3. A double-frequency CARS measurement method based on bound-state optical solitons is characterized by comprising the following steps:
step 1: the femtosecond laser outputs ultra-short pulse with pulse width of 40-200 fs and linear polarization to be incident to the electric control liquid crystal wave plate;
step 2: when the voltage applied by the electric control liquid crystal wave plate changes, the light power of the horizontal ultrashort pulse output by the reflection and transmission of the polarization beam splitter prism changes along with the voltage; the ultrashort pulse output by reflection of the polarization beam splitter prism is used as a pump light pulse of the dual-frequency CARS system, and the ultrashort pulse output by transmission is used for generating a bound-state light soliton and is used as a Stokes light pulse of the dual-frequency CARS system;
and step 3: the ultra-short pulse with adjustable light power transmitted and output by the polarization beam splitter prism sequentially enters the high nonlinear polarization-maintaining photonic crystal fiber through the half wave plate, the beam expander and the fiber coupling mirror, and the linear polarization direction of the ultra-short pulse entering the high nonlinear polarization-maintaining photonic crystal fiber is adjusted by the half wave plate, so that when the ultra-short pulse is incident along a certain specific direction, bound state light solitons are generated at the output end of the high nonlinear polarization-maintaining photonic crystal fiber; expanding the diameter of the ultra-short pulse light beam transmitted in space by using a beam expander to improve the coupling efficiency of the optical fiber coupling mirror; coupling the ultra-short pulse transmitted in space into the high nonlinear polarization-maintaining photonic crystal fiber by using a fiber coupling mirror; generating bound state optical solitons with the wavelength changing along with the incident ultrashort pulse optical power by utilizing the high nonlinear polarization maintaining photonic crystal fiber, and using the bound state optical solitons as Stokes optical pulses of a dual-frequency CARS system;
and 4, step 4: adjusting a half wave plate to enable the power component of the ultrashort pulse in the fast axis direction to be larger than that in the slow axis direction, so that the optical solitons generated in the fast axis direction have longer wavelength and the optical solitons generated in the slow axis direction have shorter wavelength; when the wavelengths of the optical solitons transmitted along the fast axis and the slow axis are both positioned in the anomalous dispersion region of the high nonlinear polarization-maintaining photonic crystal fiber, in the transmission process of the same section of high nonlinear polarization-maintaining photonic crystal fiber, the time required by the fast axis optical solitons with longer wavelengths is longer than that of the slow axis optical solitons with shorter wavelengths; when the fast/slow axis optical solitons with wavelength difference are transmitted in the high nonlinear polarization-maintaining photonic crystal fiber, the proper polarization direction of ultrashort pulse entering the high nonlinear polarization-maintaining photonic crystal fiber is adjusted, so that the time difference caused by the dispersion effect and the time difference caused by the birefringence effect are mutually compensated, and the fast axis solitons and the slow axis solitons at the output end of the high nonlinear polarization-maintaining photonic crystal fiber are mutually overlapped in the time domain to have certain wavelength difference on a spectrum, thereby generating bound state optical solitons;
and 5: bound state light solitons output by the high nonlinear polarization maintaining photonic crystal fiber are converted into light beams transmitted in space through a fiber collimation beam expanding lens and are used as Stokes light pulses of a dual-frequency CARS system; the Stokes light beams output by the fiber collimation beam expander are reflected and output by the beam combiner after being transmitted by the first reflector and the first dispersion glass, and the first dispersion glass is used for broadening Stokes light pulses and enabling the Stokes light pulses to generate linear chirp;
step 6: ultrashort pulses output by reflection of the polarization beam splitter prism are used as pumping light pulses of the dual-frequency CARS system, and are transmitted and output by the beam combiner after being sequentially transmitted by the second reflecting mirror, the adjustable space light delay line, the adjustable attenuation sheet and the second dispersive glass; adjusting the time delay of the pump light pulse by using an adjustable space light delay line to ensure that the pump light pulse and the Stokes light pulse are overlapped in time at the position of the sample to be detected; the optical power of the pump light pulse is adjusted by using the adjustable attenuation sheet, so that the optical power of the pump light pulse is approximately twice of the Stokes light pulse power, and the pump light pulse and the Stokes light pulse completely act to generate an anti-Stokes Raman scattering signal; broadening the pump light pulse by using a second dispersive glass and enabling the pump light pulse to generate linear chirp; selecting proper lengths of the first dispersive glass and the second dispersive glass to enable the Stokes light pulse and the pump light pulse to have the same linear chirp so as to realize spectral focusing;
and 7: the CARS microscopic imaging system can focus and emit the combined pumping light pulse and Stokes light pulse into a sample to be detected to excite an anti-Stokes Raman scattering signal, namely a CARS signal, collect the CARS signal generated by the sample to be detected to analyze the spectral components of the sample to be detected so as to realize chemoselective imaging, and realize the spatial distribution microscopic measurement of target molecules in the sample to be detected by changing the relative positions of a focusing light spot and the sample to be detected.
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