CN110763668B - CARS microscopic imaging device and method based on conical fiber probe excitation - Google Patents
CARS microscopic imaging device and method based on conical fiber probe excitation Download PDFInfo
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Abstract
The invention discloses a CARS microscopic imaging device and a method based on conical fiber probe excitation, the device at least comprises a femtosecond laser (1), an electric control liquid crystal wave plate (2), a polarization beam splitter prism (3), a Stokes light path part, a second fiber coupling mirror (7), a pumping light path part, a reflector (8), a pumping light path, a conical fiber beam combiner (11) and a signal acquisition and processing system (15), wherein the output time overlap and space overlap of the conical fiber beam combiner, and Stokes light pulses and pumping light pulses with the same linear chirp are incident into a sample to be detected on a three-dimensional electric control objective table to excite the CARS signal at the focus of the sample to be detected; the CARS signal is used as the input of a signal acquisition and processing system so as to realize the acquisition and processing of the CARS signal. The invention has simple structure and convenient adjustment, can realize spectrum focusing, fully utilizes the spectrum energy of the ultrashort pulse and improves the resolution of the Raman resonance spectrum.
Description
Technical Field
The invention belongs to the field of fiber optics and resonance spectrum microscopic imaging, and relates to a CARS microscopic imaging device and method.
Background
Coherent anti-Stokes Raman scattering (CARS) microscopic imaging technology is a resonance spectrum microscopic imaging technology based on four-wave mixing effect, wherein a pump light pulse and a Stokes light pulse are simultaneously incident into a sample to be detected, when the energy difference of the two light pulses is equal to the resonance energy level of a target chemical bond in the sample to be detected, the four-wave mixing effect is generated, and anti-Stokes Raman scattering light, namely a CARS signal, is generated. Therefore, the unmarked, non-contact and chemoselective microscopic imaging of the sample to be detected can be realized by detecting the spatial distribution of the CARS signal in the sample to be detected. Because the pump light pulse and the Stokes light pulse in the CARS microscopic imaging system need to be simultaneously incident to the same position of a sample to be detected so as to excite the CARS signal at a certain point position in the sample to be detected, and the focusing light spots of the two beams of light are small enough to realize three-dimensional space imaging of the sample to be detected, the phase matching condition in the four-wave mixing process is met, and the CARS signal excitation efficiency is improved. Therefore, in the traditional CARS micro-imaging system, a spatial light path is mostly used for realizing beam combination of the pump light pulse and the Stokes light pulse, and two beams of pulses are tightly focused to a sample to be measured through a high numerical aperture objective lens. However, the use of spatial beams makes the conventional CARS microscopic imaging system bulky, complicated to adjust, requiring regular maintenance by professionals, and expensive to operate. The optical fiber has the characteristics of no calibration, no maintenance, flexible and convenient spatial arrangement and the like, so that the optical fiber has the advantages of reducing the complexity of the system, improving the use efficiency of the system, reducing the operation cost of the system and the like when being used for the CARS microscopic imaging system. Therefore, the combination of fiber optic technology and CARS microscopic imaging systems has attracted intense interest to a wide range of researchers.
Disclosure of Invention
The invention aims to provide a CARS microscopic imaging device and a CARS microscopic imaging method based on conical optical fiber probe excitation. The invention abandons the space excitation light path in the traditional CARS microscopic imaging system and has the intrinsic space position coincidence characteristic and the intrinsic spectrum focusing characteristic of the pump light pulse and the Stokes light pulse.
The invention relates to a CARS microscopic imaging device based on conical fiber probe excitation, which at least comprises a femtosecond laser 1, an electric control liquid crystal wave plate 2, a polarization beam splitter prism 3, a Stokes light path part, a second fiber coupling mirror 7, a pumping light path part, a reflector 8, a pumping light path, a conical fiber beam combiner 11 and a signal acquisition and processing system 15; wherein:
the femtosecond laser 1 outputs ultra-short pulses with pulse width of hundred femtosecond magnitude and horizontal line polarization, and the ultra-short pulses are incident to the electric control liquid crystal wave plate 2; ultrashort pulses transmitted and output by the electric control liquid crystal wave plate 2 are divided into a stokes light path part transmitted and output and a reflection output pumping light path part through the polarization beam splitter prism 3; the Stokes light path part consists of a first optical fiber coupling mirror 4, a high nonlinear polarization-maintaining photonic crystal fiber 5 and an optical fiber collimation beam expander 6 which are sequentially connected; one output end of the polarization beam splitter prism 3 is connected with the input end of the first optical fiber coupling mirror 4, and the output end of the optical fiber collimation beam expander mirror 6 is connected with the input end of the second optical fiber coupling mirror 7; the output end of the second fiber coupling mirror 7 emits a Stokes light path to the connecting reflecting mirror 8; the pumping light path part consists of an adjustable space light delay line 9 and a third optical fiber coupling mirror 10 which are connected in sequence; the reflector 8 is incident to an adjustable space light delay line 9; the output end of the third fiber coupling mirror 10 is connected with the tapered fiber combiner 11, and the stokes light pulse and the pump light pulse which are output by the tapered fiber combiner and have the same linear chirp are incident into a sample to be detected on the three-dimensional electronic control objective table in time overlapping and space overlapping so as to excite the CARS signal at the focus of the sample to be detected; the CARS signal is used as the input of a signal acquisition and processing system to realize the acquisition and processing of the CARS signal;
the electric control liquid crystal wave plate 2 controls the polarization state of the ultra-short pulse transmitted and output by the external voltage, so that the polarization state of the ultra-short pulse continuously changes among horizontal line polarization, elliptical polarization, circular polarization and vertical line polarization, and the electric control continuous adjustment of the output light power is realized;
the polarization beam splitter prism 3 is used for realizing polarization-dependent beam splitting;
the first optical fiber coupling mirror 4 is used for coupling the ultrashort pulse transmitted and output by the polarization beam splitter prism 3 into the high nonlinear polarization-maintaining photonic crystal fiber;
the high nonlinear polarization-maintaining photonic crystal fiber 5 is used for generating optical solitons with the wavelength capable of being continuously adjusted in a large range and used as Stokes optical pulses;
the optical fiber collimation beam expander 6 is used for collimating stokes light pulses output by beam expansion;
the second fiber coupling mirror 7 is used for coupling stokes light pulses output by the collimation and beam expansion of the fiber collimation and beam expansion mirror 6 to a stokes light transmission fiber 111 of the tapered fiber beam combiner 11 through the second fiber coupling mirror 7;
the adjustable space light delay line 9 is used for adjusting the time delay of the pump light pulse so that the pump light pulse and the Stokes light pulse are simultaneously incident into a sample to be measured;
the third fiber coupling mirror 10 is configured to couple the ultra-short pulse with variable delay output by the adjustable spatial light delay line 9 to the pump light transmission fiber 112 of the tapered fiber combiner 11 through the third fiber coupling mirror 10;
the tapered fiber combiner 11 is used for enabling the Stokes light pulses and the pump light pulses to have the same linear chirp and for focusing the Stokes light pulses and the pump light pulses through the fiber.
The invention discloses a CARS microscopic imaging method based on conical fiber probe excitation, which comprises the following steps:
step 1: the femtosecond laser outputs hundred-femtosecond-magnitude horizontally-polarized ultrashort pulses, and the ultrashort pulses are incident to the electric control liquid crystal wave plate; the transmission output of the ultra-short pulse has a polarization state which can be continuously changed among horizontal line polarization, elliptical polarization, circular polarization and vertical line polarization through the voltage regulation added to the electric control liquid crystal wave plate, the ultra-short pulse is incident to the polarization beam splitter prism to realize polarization-related beam splitting, wherein the polarization state of the transmission output light pulse is horizontal line polarization, and the polarization state of the reflection output light pulse is vertical line polarization direction; the light power of the polarization beam splitter prism for transmitting and outputting the ultrashort pulse and reflecting and outputting the ultrashort pulse is changed by changing the polarization state of the incident light to the polarization beam splitter prism, and the ultrashort pulse sum with adjustable power transmitted and output by the polarization beam splitter prism is obtained;
step 2: the ultra-short pulse with adjustable power transmitted and output by the polarization beam splitter prism is coupled to the high nonlinear polarization-maintaining photonic crystal fiber through the first fiber coupling mirror; when the ultrashort pulse is transmitted in the high nonlinear polarization-maintaining photonic crystal fiber, optical solitons with the wavelength moving towards the long wavelength direction are generated, and the optical solitons generated by the self-frequency shift effect of the solitons of the high nonlinear polarization-maintaining photonic crystal fiber are used as Stokes optical pulses;
and step 3: the ultra-short pulse with adjustable power reflected and output by the polarization beam splitter prism is incident to the adjustable space light delay line through the reflector, the time delay of the light beam is realized through the adjustable space light delay line, and the ultra-short pulse with variable time delay output by the adjustable space light delay line is used as a pump light pulse;
and 4, step 4: the Stokes light pulses are coupled into a Stokes light transmission fiber of the tapered fiber combiner through a second fiber coupling mirror, the pump light pulses are coupled into a pump light transmission fiber of the tapered fiber combiner through a third fiber coupling mirror, and the Stokes light pulses and the pump light pulses are respectively transmitted through the respective transmission fibers, combined at the position of the combiner and output to the tapered excitation fiber; adjusting the lengths of the Stokes light transmission fiber and the pump light transmission fiber to enable the Stokes light pulse and the pump light pulse to have the same linear chirp so as to realize spectral focusing; the optical fiber focusing of the Stokes light pulse and the pump light pulse by the tapered optical fiber is realized by adjusting the length of the tapered optical fiber taper region and the diameter of an output end;
and 5: adjusting an adjustable space light delay line to enable the Stokes light pulse and the pump light pulse to realize time overlapping at the output end of the tapered optical fiber beam combiner;
step 6: the method comprises the steps that Stokes light pulses and pumping light pulses which are output by a conical optical fiber beam combiner and have the same linear chirp are incident into a sample to be detected on a three-dimensional electric control objective table so as to excite a CARS signal at the focus of the sample to be detected;
and 7: the CARS signal transmitted and output by a sample to be detected is collected by a light-collecting objective lens and filtered by an optical filter to remove residual pump light pulse and Stokes light pulse, and then is incident to a signal acquisition and processing system to realize acquisition and processing of the CARS signal;
and 8: adjusting the Stokes light pulse wavelength to realize complete Raman resonance spectrum measurement of a sample to be measured at a focus, moving the focus point by point in the sample to be measured by moving the three-dimensional electric control object stage, and realizing the measurement of CARS signals at different positions in the sample to be measured, namely realizing the unmarked, non-contact and chemically selective CARS microscopic imaging of target chemical bonds in the sample to be measured.
Compared with the traditional CARS microscopic imaging technology, the invention has the following technical advantages: 1) the conical optical fiber beam combiner is used for combining and focusing the pump light pulse and the Stokes light pulse into a sample to be detected, the space light combination and the excitation objective lens in the traditional CARS microscopic imaging system are abandoned, and the device is simple in structure and convenient to adjust; 2) when the ultrashort pulse is transmitted in the optical fiber, the ultrashort pulse generates linear chirp due to the influence of optical fiber dispersion, the lengths of the pump light transmission fiber and the Stokes light transmission fiber are adjusted, and the pump light pulse and the Stokes light pulse can have the same linear chirp, so that spectrum focusing can be realized, the spectrum energy of the ultrashort pulse is fully utilized, and the resolution of a Raman resonance spectrum is improved; 3) the pump light pulse and the Stokes light pulse are output by the same tapered optical fiber and have the characteristic of substantial spatial overlapping, so that the system is convenient, simple and reliable to adjust.
Drawings
FIG. 1 is a schematic structural diagram of a CARS micro-imaging device based on tapered fiber probe excitation according to the present invention;
fig. 2 is a schematic diagram of a tapered excitation fiber structure.
Reference numerals are as follows:
1. the device comprises a femtosecond laser, 2, an electric control liquid crystal wave plate, 3, a polarization beam splitter prism, 4, a first optical fiber coupling mirror, 5, a high nonlinear polarization-maintaining photonic crystal optical fiber, 6, an optical fiber collimation beam expander, 7, a second optical fiber coupling mirror, 8, a reflector, 9, an adjustable space optical delay line, 10, a third optical fiber coupling mirror, 11, a tapered optical fiber beam combiner, 12, a three-dimensional electric control objective table, 13, a light collecting objective lens, 14, an optical filter, 15 and a signal acquisition and processing system
91. The device comprises a first right-angle reflecting prism, a second right-angle reflecting prism, a high-precision electric control displacement table and a second right-angle reflecting prism, wherein the first right-angle reflecting prism is 92.
111. Stokes light transmission fiber 112, pump light transmission fiber 113, beam combiner 114 and tapered excitation fiber.
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 structural diagram of a CARS microscopic imaging device based on tapered fiber probe excitation according to the present invention. The device comprises a femtosecond laser 1, an electric control liquid crystal wave plate 2, a polarization beam splitter prism 3, a Stokes light path (consisting of a first optical fiber coupling mirror 4, a high nonlinear polarization-maintaining photonic crystal optical fiber 5 and an optical fiber collimation beam expander 6), a second optical fiber coupling mirror 7, a reflector 8, a pumping light path (consisting of an adjustable space light delay line 9 (consisting of two right- angle reflecting prisms 91 and 92 and a high-precision electric control displacement platform 93) and a third optical fiber coupling mirror 10), a tapered optical fiber beam combiner 11 (consisting of a Stokes light transmission optical fiber 111, a pumping light transmission optical fiber 112, a beam combiner 113 and a tapered excitation optical fiber 114), a three-dimensional electric control objective table 12, a light collection objective 13, an optical filter 14 and a signal collection and processing system 15.
The femtosecond laser 1 outputs ultra-short pulses with pulse width of hundred femtosecond magnitude and horizontal line polarization, and the ultra-short pulses are incident to the electric control liquid crystal wave plate 2; ultra-short pulses transmitted and output by the electric control liquid crystal wave plate 2 are divided into a transmission beam and a reflection beam through the polarization beam splitter prism;
the ultrashort pulse transmitted and output by the polarization beam splitter prism 3 is coupled into the high nonlinear polarization-maintaining photonic crystal fiber 5 through the first fiber coupling mirror 4, and when the ultrashort pulse light is transmitted in the high nonlinear polarization-maintaining photonic crystal fiber 5, a soliton self-frequency shift effect is generated, light solitons with the wavelength moving towards the long wavelength direction are generated, and the ultrashort pulse light is used as a Stokes light pulse; the output end of the high nonlinear polarization-maintaining photonic crystal fiber 5 is connected with a fiber collimation beam expander 6; the stokes light pulse output by the collimation and beam expansion of the optical fiber collimation and beam expansion lens 6 is coupled to a stokes light transmission optical fiber 111 of the conical optical fiber beam combiner 11 through a second optical fiber coupling lens 7;
the ultrashort pulse reflected and output by the polarization beam splitter prism 3 is incident to an adjustable space light delay line 9 through a reflecting mirror 8. In the adjustable spatial light delay line 9: the first right-angle reflecting prism 91 reflects the incident ultrashort pulse to the second right-angle reflecting mirror 92 fixed on the high-precision electronic control displacement stage 93, and simultaneously reflects and outputs the optical pulse reflected by the second right-angle reflecting prism 92 through the other right-angle side, and the high-precision electronic control displacement stage 93 is used for adjusting the time delay of the stokes optical pulse. The ultra-short pulse with variable time delay output by the adjustable space optical time delay line 9 is incident to the tapered optical fiber beam combiner 11 through the third optical fiber coupling mirror 10. In the tapered optical fiber combiner 11, stokes light pulses are transmitted to a combiner 113 through a stokes light transmission optical fiber 111 and are combined with pump light pulses transmitted by a pump light transmission optical fiber 112 at the position, and the combined stokes light pulses and pump light pulses are transmitted through a tapered excitation optical fiber 114 and focused on a sample to be measured on a three-dimensional electric control object stage 12; the lengths of the stokes light transmission fiber 111 and the pump light transmission fiber 112 are adjusted, so that stokes light pulses and pump light pulses have the same linear chirp, spectrum focusing is realized, and the utilization rate of ultrashort pulse light spectrums and the resolution capability of Raman resonance spectrums in a CARS microscopic imaging system are improved;
the CARS signal generated by the sample to be detected is incident to a signal collecting and detecting part consisting of a light collecting objective lens 13, an optical filter 14 and a signal collecting and processing system 15. The CARS transmission signal generated by the sample to be detected is collected by the light collecting objective lens 13 and then is incident to the optical filter 14, and the CARS transmission signal output by the optical filter 14 is incident to the signal acquisition and processing system 15.
The electric control liquid crystal wave plate 2 can control the polarization state of the ultra-short pulse output by transmission through an external voltage, so that the polarization state of the ultra-short pulse output by transmission can be continuously changed among horizontal line polarization, elliptical polarization, circular polarization and vertical line polarization, and the electric control continuous adjustment of the output light power of the polarization beam splitter prism 3 can be realized by combining the polarization beam splitter prism 3.
The high nonlinear polarization-maintaining photonic crystal fiber 5 is used for generating optical solitons with the wavelength capable of being continuously adjusted in a large range and used as Stokes optical pulses.
The adjustable space light delay line 9 is used for adjusting the time delay of the pump light pulse, so that the pump light pulse and the Stokes light pulse are simultaneously incident into a sample to be measured.
The tapered excitation fiber 114 is made by a fiber tapering technique, and the output end diameter of the tapered fiber is reduced to 1 μm while ensuring high-efficiency power transmission by selecting a suitable tapered fiber taper region length and output end diameter, so as to realize fiber focusing of the tapered fiber on stokes light pulses and pump light pulses.
The invention discloses a CARS microscopic imaging method based on conical fiber probe excitation, which mainly comprises the following steps:
step 1: the femtosecond laser outputs hundred-femtosecond-magnitude horizontally-polarized ultrashort pulses to be incident to the electric control liquid crystal wave plate. The electric control liquid crystal wave plate can adjust the polarization state of the transmission output ultrashort pulse through the applied voltage, so that the electric control liquid crystal wave plate can continuously change among horizontal line polarization, elliptical polarization, circular polarization and vertical line polarization. Ultrashort pulses with continuously variable polarization states output by the electric control liquid crystal wave plate are incident to the polarization beam splitter prism to realize polarization-dependent beam splitting, wherein the polarization state of the transmitted output light pulse is horizontal line polarization, and the polarization state of the reflected output light pulse is vertical line polarization. The light power of the polarization beam splitter prism for transmitting and reflecting the output ultrashort pulse can be changed by changing the polarization state of the incident light to the polarization beam splitter prism. Therefore, the electric control continuous adjustment of the output light power of the polarization beam splitter prism can be realized by the combined use of the electric control liquid crystal wave plate and the polarization beam splitter prism;
step 2: the ultra-short pulse with adjustable power transmitted and output by the polarization beam splitter prism is coupled to the high nonlinear polarization-maintaining photonic crystal fiber through the first fiber coupling mirror. When the ultrashort pulse is transmitted in the high nonlinear polarization-maintaining photonic crystal fiber, due to the influence of fiber dispersion, self-phase modulation and Raman scattering effect in the pulse, optical solitons with the wavelength moving towards the long wavelength direction are generated, and the wavelength of the optical solitons is approximately linearly increased along with the increase of the power of the incident ultrashort pulse light. The optical solitons generated by the soliton self-frequency shift effect of the high nonlinear polarization-maintaining photonic crystal fiber are very suitable for being used as Stokes light pulses of a CARS microscopic imaging system due to the characteristics of continuous and adjustable wavelength and time synchronization with the nature of pumping pulses;
and step 3: the ultra-short pulse with adjustable power transmitted and output by the polarization beam splitter prism is incident to an adjustable space light delay line through a reflector, the adjustable space light delay line realizes the time delay of a light beam by adjusting the position of a high-precision electric control displacement table, and the time-delay variable ultra-short pulse output by the adjustable space light delay line is used as a pumping light pulse of a CARS (coherent anti-interference optical scanning) microscopic imaging system;
and 4, step 4: stokes light pulses are coupled into a Stokes light transmission fiber of the tapered fiber combiner through the second fiber coupling mirror, pump light pulses are coupled into a pump light transmission fiber of the tapered fiber combiner through the third fiber coupling mirror, and the Stokes light pulses and the pump light pulses are respectively transmitted through the respective transmission fibers, combined at the position of the combiner and output to the tapered excitation fiber. The lengths of the Stokes light transmission fiber and the pump light transmission fiber of the tapered fiber combiner are adjusted, so that Stokes light pulses and pump light pulses at the output end of the tapered excitation fiber have the same linear chirp, spectrum focusing is realized, and the utilization efficiency of an ultra-short pulse light spectrum and the vibration spectrum resolution capability of a CARS microscopic imaging system are improved. The length of a conical area of the conical optical fiber and the diameter of an output end are adjusted through an optical fiber tapering technology, the diameter of the output end of the conical optical fiber is reduced to 1 mu m while high-efficiency power transmission is ensured, and optical fiber focusing of the conical optical fiber on Stokes light pulses and pump light pulses is realized;
and 5: adjusting an adjustable space light delay line to enable the Stokes light pulse and the pump light pulse to realize time overlapping at the output end of the tapered optical fiber beam combiner;
step 6: the method comprises the steps that Stokes light pulses and pumping light pulses which are output by a conical optical fiber beam combiner and have the same linear chirp are incident into a sample to be detected on a three-dimensional electric control objective table so as to excite a CARS signal at the focus of the sample to be detected;
and 7: the CARS signal transmitted and output by a sample to be detected is collected by a light-collecting objective lens and filtered by an optical filter to remove residual pump light pulse and Stokes light pulse, and then is incident to a signal acquisition and processing system to realize acquisition and processing of the CARS signal;
and 8: the complete Raman resonance spectrum measurement of a sample to be measured at a focus can be realized by adjusting the Stokes light pulse wavelength, and the CARS signals at different positions in the sample to be measured can be measured by moving the three-dimensional electric control object stage to enable the focus to move point by point in the sample to be measured, so that the CARS microscopic imaging without mark, non-contact and chemical selectivity of target chemical bonds in the sample to be measured can be realized by adjusting the Stokes light wavelength and moving the three-dimensional electric control object stage.
Claims (4)
1. A CARS microscopic imaging device based on conical fiber probe excitation is characterized by at least comprising a femtosecond laser (1), an electric control liquid crystal wave plate (2), a polarization beam splitter prism (3), a Stokes light path part, a second fiber coupling mirror (7), a pumping light path part, a reflector (8), a pumping light path, a conical fiber beam combiner (11) and a signal acquisition and processing system (15); wherein: the femtosecond laser (1) outputs ultra-short pulses with hundred femtosecond magnitude pulse width and horizontal line polarization, and the ultra-short pulses are incident to the electric control liquid crystal wave plate (2); ultrashort pulses transmitted and output by the electric control liquid crystal wave plate (2) are divided into a Stokes light path part for transmission output and a pump light path part for reflection output by the polarization beam splitter prism (3); the Stokes light path part consists of a first optical fiber coupling mirror (4), a high nonlinear polarization-maintaining photonic crystal fiber (5) and an optical fiber collimation beam expander mirror (6) which are sequentially connected; one output end of the polarization beam splitter prism (3) is connected with the input end of the first optical fiber coupling mirror (4), and the output end of the optical fiber collimation beam expander mirror (6) is connected with the input end of the second optical fiber coupling mirror (7); ultrashort pulses reflected and output by the polarization beam splitter prism (3) are incident to an adjustable space light delay line (9) through the reflector (8); the pumping light path part consists of an adjustable space light delay line (9) and a third optical fiber coupling mirror (10) which are connected in sequence; the output end of the third optical fiber coupling mirror (10) is connected with the tapered optical fiber beam combiner (11), and the Stokes light pulse and the pump light pulse which are output by the tapered optical fiber beam combiner and have the same linear chirp are incident into a sample to be detected on the three-dimensional electric control object stage so as to excite the CARS signal at the focus of the sample to be detected; the CARS signal is used as the input of a signal acquisition and processing system to realize the acquisition and processing of the CARS signal;
the electric control liquid crystal wave plate (2) controls the polarization state of the ultra-short pulse transmitted and output by the external voltage, so that the polarization state of the ultra-short pulse continuously changes among horizontal line polarization, elliptical polarization, circular polarization and vertical line polarization, and the electric control continuous adjustment of the output light power is realized;
the polarization beam splitter prism (3) is used for realizing polarization-dependent beam splitting;
the first optical fiber coupling mirror (4) is used for coupling the ultra-short pulse transmitted and output by the polarization beam splitter prism (3) into the high nonlinear polarization-maintaining photonic crystal fiber;
the high nonlinear polarization-maintaining photonic crystal fiber (5) is used for generating optical solitons with the wavelength capable of being continuously adjusted in a large range and used as Stokes optical pulses;
the optical fiber collimation beam expander lens (6) is used for collimating Stokes light pulses output by beam expansion;
the second optical fiber coupling mirror (7) is used for coupling the Stokes light pulse output by the collimation and beam expansion of the optical fiber collimation and beam expansion mirror (6) to a Stokes light transmission optical fiber (111) of the conical optical fiber beam combiner (11) through the second optical fiber coupling mirror (7);
the adjustable space light delay line (9) is used for adjusting the time delay of the pump light pulse to ensure that the pump light pulse
Simultaneously injecting the pulse and the Stokes light pulse into a sample to be detected;
the third fiber coupling mirror (10) is used for coupling the ultrashort pulse with variable time delay output by the adjustable space light time delay line (9) to a pump light transmission fiber (112) of the tapered fiber combiner (11) through the third fiber coupling mirror (10); the tapered fiber combiner (11) is used for enabling the Stokes light pulses and the pump light pulses to have the same linear chirp and enabling the Stokes light pulses and the pump light pulses to be focused through the fiber.
2. The CARS microscopic imaging device based on tapered fiber probe excitation according to claim 1, characterized in that the tapered fiber combiner (11) is composed of a Stokes light transmission fiber (111), a pump light transmission fiber (112), a combiner (113) and a tapered excitation fiber (114); the Stokes light pulses are transmitted to the beam combiner (113) through the Stokes light transmission optical fiber (111) and are combined with the pump light pulses transmitted by the pump light transmission optical fiber (112) at the position, and the combined Stokes light pulses and pump light pulses are transmitted through the tapered excitation optical fiber (114) and focused on a sample to be measured positioned on the three-dimensional electric control object stage (12).
3. The CARS microimaging device based on tapered fiber probe excitation according to claim 2, characterized in that the tapered excitation fiber (114) is made of a common single mode fiber by fiber tapering, and the diameter of the tapered region is less than 500 nm.
4. A CARS microscopic imaging method based on conical fiber probe excitation is characterized by comprising the following steps:
step 1: the femtosecond laser outputs hundred-femtosecond-magnitude horizontally-polarized ultrashort pulses, and the ultrashort pulses are incident to the electric control liquid crystal wave plate; the transmission output of the ultra-short pulse has a polarization state which can be continuously changed among horizontal line polarization, elliptical polarization, circular polarization and vertical line polarization through the voltage regulation added to the electric control liquid crystal wave plate, the ultra-short pulse is incident to the polarization beam splitter prism to realize polarization-related beam splitting, wherein the polarization state of the transmission output light pulse is horizontal line polarization, and the polarization state of the reflection output light pulse is vertical line polarization direction; the light power of the polarization beam splitter prism for transmitting and outputting the ultrashort pulse and reflecting and outputting the ultrashort pulse is changed by changing the polarization state of the incident light to the polarization beam splitter prism, and the ultrashort pulse sum with adjustable power transmitted and output by the polarization beam splitter prism is obtained;
step 2: the ultra-short pulse with adjustable power transmitted and output by the polarization beam splitter prism is coupled to the high nonlinear polarization-maintaining photonic crystal fiber through the first fiber coupling mirror; when the ultrashort pulse is transmitted in the high nonlinear polarization-maintaining photonic crystal fiber, optical solitons with the wavelength moving towards the long wavelength direction are generated, and the optical solitons generated by the self-frequency shift effect of the solitons of the high nonlinear polarization-maintaining photonic crystal fiber are used as Stokes optical pulses;
and step 3: the ultra-short pulse with adjustable power reflected and output by the polarization beam splitter prism is incident to the adjustable space light delay line through the reflector, the time delay of the light beam is realized through the adjustable space light delay line, and the ultra-short pulse with variable time delay output by the adjustable space light delay line is used as a pump light pulse;
and 4, step 4: the Stokes light pulses are coupled into a Stokes light transmission fiber of the tapered fiber combiner through a second fiber coupling mirror, the pump light pulses are coupled into a pump light transmission fiber of the tapered fiber combiner through a third fiber coupling mirror, and the Stokes light pulses and the pump light pulses are respectively transmitted through the respective transmission fibers, combined at the position of the combiner and output to the tapered excitation fiber; adjusting the lengths of the Stokes light transmission fiber and the pump light transmission fiber to enable the Stokes light pulse and the pump light pulse to have the same linear chirp so as to realize spectral focusing; the optical fiber focusing of the Stokes light pulse and the pump light pulse by the tapered optical fiber is realized by adjusting the length of the tapered optical fiber taper region and the diameter of an output end;
and 5: adjusting an adjustable space light delay line to enable the Stokes light pulse and the pump light pulse to realize time overlapping at the output end of the tapered optical fiber beam combiner;
step 6: the method comprises the steps that Stokes light pulses and pumping light pulses which are output by a conical optical fiber beam combiner and have the same linear chirp are incident into a sample to be detected on a three-dimensional electric control objective table so as to excite a CARS signal at the focus of the sample to be detected;
and 7: the CARS signal transmitted and output by a sample to be detected is collected by a light-collecting objective lens and filtered by an optical filter to remove residual pump light pulse and Stokes light pulse, and then is incident to a signal acquisition and processing system to realize acquisition and processing of the CARS signal;
and step 8: adjusting the Stokes light pulse wavelength to realize complete Raman resonance spectrum measurement of a sample to be measured at a focus, moving the focus point by point in the sample to be measured by moving the three-dimensional electric control object stage, and realizing the measurement of CARS signals at different positions in the sample to be measured, namely realizing the unmarked, non-contact and chemically selective CARS microscopic imaging of target chemical bonds in the sample to be measured.
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