CN104316180A - Double-optical frequency comb optical imaging method based on continuous frequency stabilized laser - Google Patents

Abstract

The invention discloses a dual optical frequency comb optical imaging method based on continuous frequency-stabilized lasers. The optical imaging method locks two optical frequency comb seed sources on a stable external atomic clock through a repetition frequency control module. The interaction between the high-frequency laser and the output laser of two optical frequency comb seed sources extracts the electrical signal carrying the frequency instability of the optical comb, and distributes and processes the power of the RF signal, and a part of it is directly used for feedback control The characteristics of the laser resonator of the two optical frequency comb seed sources are used to stabilize the output carrier envelope phase frequency of the semiconductor laser, and the other part is used to mix with the periodic interference spectrum signal generated by the dual optical comb imaging system, further combining the optical comb The frequency drift of the system is offset, so as to control the measurement accuracy of the entire dual-comb imaging system from two aspects, and realize fast and ultra-high-resolution optical comb coherent imaging.

Description

Dual Optical Frequency Comb Optical Imaging Method Based on Continuous Frequency Stabilized Laser

technical field

The invention belongs to the technical field of ultrafast lasers, in particular to a dual optical frequency comb optical imaging method based on continuous frequency-stabilized lasers.

Background technique

The development of optical microscopic imaging technology has a long history, and it has been continuously improved along with the deepening of human exploration of the microcosm. As early as the first century BC, people discovered that water droplets could be used to observe the magnified image of an object. The spatial resolution of traditional optical imaging systems is limited by the diffraction limit. Generally speaking, the spatial resolution limited by the diffraction limit of optical imaging systems is about half of the wavelength of the probe light. For object details smaller than this imaging limit, traditional optical systems will powerless. In the 1980s, the emergence of non-optical scanning probe microscopy, especially atomic force microscopy, can advance the resolution of imaging to nanometer-level precision, but these microscopy techniques either have very small penetration depths, or can only give The information on the surface of the object, and to varying degrees, there are problems such as complex system structure and harsh imaging detection environment. With the development and maturity of laser technology, applying laser, a tool with good coherence, directionality and energy density, to optical microscopy imaging can provide important optical information (such as polarization state, refractive index, Spectrum, etc.), and non-destructive biological living detection. Among them, femtosecond optical frequency combs (referred to as optical combs) emerging in recent years can be directly used as light sources in nonlinear optical imaging processes. There are many nonlinear effects that can be used for optical imaging, such as: two-photon absorption, second harmonic (SHG), third harmonic (THG), coherent anti-Stokes Raman scattering (CARS), Kerr effect, etc.

On the other hand, in order to construct a femtosecond optical frequency comb with high frequency stability in the time domain and frequency domain, it is necessary to combine the repetition frequency signal ( f _r ) of the output pulse train of the mode-locked pulsed laser with the carrier envelope phase frequency signal ( f _ceo ) locking, that is, to ensure that the interval between each tooth of the frequency comb is stable, and the whole does not drift in the frequency domain. Among them, the repetition frequency signal of the optical comb is an electrical signal that can be directly detected. By mixing it with the standard signal controlled by the atomic clock and feedback controlling the laser cavity length, the repetition frequency locking of the optical comb can be realized. However, the detection and control process of the phase drift frequency of the optical comb carrier envelope due to the difference between the group velocity and the phase velocity during the pulse propagation process is relatively complicated. Usually, it is necessary to perform power amplification and spectral broadening on the output light of the optical comb, and then use a common The linear or non-collinear f-2f self-reference optical system performs optical frequency doubling and optical beam combining beat frequency, and extracts the carrier envelope phase drift frequency. In the above-mentioned process, not only the dispersion characteristics and polarization state of the pulse need to be well controlled, but also the temperature of the nonlinear crystal, the phase matching degree of the entire optical system, and the adjustment accuracy and stability of the optical path all have higher requirements. Requirements, these will undoubtedly have a negative impact on the application and promotion of optical frequency comb technology.

Contents of the invention

The purpose of the present invention is to provide a dual optical frequency comb optical imaging method based on continuous frequency stabilized lasers according to the shortcomings of the above-mentioned prior art. The optical imaging method locks two optical frequency comb seed sources through a repetition rate control module On a stable external atomic clock, at the same time, through the interaction between the continuous frequency-stabilized laser and the output lasers of two optical frequency comb seed sources, the electrical signal carrying the frequency instability of the optical comb is extracted, and the signal is processed into a radio frequency signal. Power distribution and processing, a part of which is directly used for feedback control of the laser resonator characteristics of the two optical frequency comb seed sources to stabilize the output carrier envelope phase frequency of the semiconductor laser, and the other part is used for the period generated by the dual optical comb imaging system Frequency mixing is performed on the interferometric spectrum signal to further offset the frequency drift of the optical comb system, so as to control the measurement accuracy of the entire dual optical comb imaging system from two aspects, and realize fast and ultra-high resolution optical comb coherent imaging.

The object of the present invention is realized by the following technical solutions:

A dual-optical frequency comb optical imaging method based on continuous frequency-stabilized lasers, involving two optical frequency comb seed sources, is characterized in that the optical imaging method includes the following steps: the respective output of the two optical frequency comb seed sources The laser is divided into three paths;

In the first way, the output lasers of the two optical frequency comb seed sources respectively enter the frequency control module to lock the repetition frequency signal of the optical frequency comb seed source on the external atomic clock;

In the second way, the output lasers of the two optical frequency comb seed sources and the output lasers of the continuous frequency-stabilized laser generation module are beaten in the continuous frequency-stabilized laser and the dual-comb interaction module to generate two similar frequencies. The beat frequency signal is filtered out to make a difference frequency to obtain a radio frequency signal f ₋ ; the radio frequency signal f ₋ is divided into three equivalent signals f ₁ , f ₂ and f ₃ through the radio frequency signal power distribution and processing module, Wherein the signals f1 and f2 are respectively fed back to the electro-optical modulator _{and the} semiconductor laser in the two optical frequency comb seed sources to stabilize the carrier envelope phase frequency of the output laser light from the two optical frequency comb seed sources, The signal f3 is amplified into a signal nf3 by a frequency multiplier and enters _the sample _data acquisition and processing module;

In the third way, the output laser light of the first optical frequency comb seed source is incident on the sample to be tested as the probe light, and the output laser light of the second optical frequency comb seed source is used as the reference light to communicate with the detection light. Beat the light frequency to obtain the interference spectrum signal f _i ; the interference spectrum signal f _i then enters the sample data acquisition and processing module and mixes with the signal nf ₃ to offset the frequency instability to obtain the spectral signal f _signal , and restore the spectral signal f _signal point by point to realize the optical imaging of the sample to be tested.

The output laser frequencies of the two optical frequency comb seed sources are respectively f _comb1 =nf _rep +f _ceo and f _comb2 =n(f _rep +Δf _rep )+f _ceo ^' , where f _rep is the first optical The repetition frequency of the frequency comb seed source , Δf _rep is the slight difference between the repetition frequency of the second optical frequency comb seed source and the first optical frequency comb seed source, and f _ceo and f _ceo ^' represent the first The carrier envelope phase shift frequency of the optical frequency comb seed source of the first station and the optical frequency comb seed source of the second station.

The output laser of the continuous frequency-stabilized laser generating module refers to a single longitudinal mode laser with a laser frequency linewidth on the order of Hz.

The laser resonator in the optical frequency comb seed source is provided with an electro-optic modulator and a semiconductor laser; the signal f1 is converted into a DC voltage and acts on the electro-optic modulator to change _the refractive index of the electro-optic modulator to Adjusting the chirp amount of the laser resonator and compensating the mismatch of the cavity length; the signal f2 is fed back to the semiconductor laser, and _the feedback controls the current of the semiconductor laser to stabilize the noise characteristics of the laser resonator .

The frequency of the detection light is f _comb1 =nf _rep +f _ceo , the frequency of the reference light is f _comb2 =n(f _rep +Δf _rep )+f _ceo ^' , the detection light and the reference light are photographed The interference spectrum signal f _i composed of a series of radio frequency signals with an interval of _Δfrep is obtained after frequency .

The advantages of the present invention are:

1) The dual-comb optical imaging method based on a small repetition frequency difference can simultaneously collect spectral information and high-resolution topographical images in a wide frequency range generated by particle transitions, and its device has a fast response rate and high acquisition speed;

2) All spectral elements of the sample to be tested can be measured simultaneously on one photodetector, thus ensuring the consistency of the spectrum; in addition, the high-precision optical frequency comb ensures the reproducibility and accuracy of the wave number scale;

3) The dual optical frequency comb system required for imaging can transmit the frequency drift of the optical comb system as an electrical signal through a continuous frequency-stabilized laser without the need to accurately detect the pulse carrier envelope phase signal, and control it , thereby greatly reducing the complexity and maintenance difficulty of the optical system, and enhancing the compactness and applicability of the entire optical comb imaging device;

4) The electrical signal carrying the characteristics of the optical comb generated by the optical comb and the continuous frequency-stabilized laser has multiple utilization values: on the one hand, it feeds back the pumping current of the laser cavity of the optical comb seed source and the electro-optic modulator in the cavity, and stabilizes the optical comb light source. On the other hand, it mixes with the interference spectrum signal obtained in the optical comb imaging process to further offset the measurement error caused by the frequency drift of the optical comb system; the entire imaging device ensures the accuracy of the imaging spectrum from multiple angles. High precision output;

5) The pulse width of the laser output by the optical frequency comb is generally on the order of femtoseconds (10 ^-15 s), and even narrower pulse output can be obtained by controlling the high-order dispersion of the laser, which is equivalent to improving the accuracy of the optical probe. Conducive to the realization of super-resolution spectral detection and microscopic imaging technology;

6) The optical frequency comb can expand the frequency domain through components such as photonic crystal fibers, so that its output frequency band can cover a wide range of ultraviolet, visible and infrared; the dual-comb imaging system can make full use of this feature and use it at the same time Multiple molecular vibration modes in a substance molecule are resonantly enhanced to generate corresponding spectral signals, so it has significant advantages in the process of non-invasive spectral identification and microscopic imaging of biological systems and other complex systems containing multiple components;

7) The repetition frequency of the optical frequency comb is generally on the order of hundreds of megahertz (10 ⁶ Hz) to several gigahertz (10 ⁹ Hz), and its output pulse can usually reach the intensity of hundreds of watts through the power amplifier; it has Ultrashort laser pulses with high peak power and low single-pulse energy can minimize the photoinduced damage to biological samples. need.

Description of drawings

Fig. 1 is a schematic diagram of the device structure in Embodiment 1 of the present invention;

2 is a schematic diagram of sample scanning and imaging using an all-fiber dual-comb system in Embodiment 2 of the present invention;

3 is a schematic diagram of coherent anti-Stokes Raman scattering imaging using a half-space, half-fiber dual-comb system in Embodiment 3 of the present invention.

Detailed ways

The features of the present invention and other relevant features are described in further detail below in conjunction with the accompanying drawings through the embodiments, so as to facilitate the understanding of those skilled in the art:

As shown in Figure 1-3, the marks 1-31 in the figure are: optical frequency comb seed source 1, optical frequency comb seed source 2, repetition frequency locking module 3, continuous frequency stabilized laser generation module 4, continuous frequency stabilized laser and dual light Comb interaction module 5, RF signal power distribution and processing module 6, frequency multiplier 7, dual optical frequency comb optical imaging module 8, sample data acquisition and processing module 9, computer 10, optical fiber wavelength division multiplexer 11, gain fiber 12. Fiber optic isolator 13, fiber coupler 14, fiber optic polarization controller 15, optical motor delay module 16, polarization beam splitter 17, dichroic mirror 18, scanning galvanometer 19, total reflection mirror 20, microscope Objective lens 21, one-dimensional sample stage 22, spatial bandpass filter 23, intracavity polarization beam splitter 24, intracavity half-wave plate 25, oblique pair 26, photonic crystal fiber 27, chirped mirror 28, spatial low frequency filter 29. Three-dimensional sample stage 30, spatial high-frequency filter 31;

Among them, LD stands for semiconductor laser, PZT stands for piezoelectric ceramic crystal, EOM stands for electro-optic modulator, and SESAM stands for semiconductor saturable absorber mirror;

The solid line in the figure represents the light propagation route, and the dotted line represents the circuit transmission route.

Embodiment 1: As shown in Figure 1, this embodiment specifically relates to a dual-optical frequency comb optical imaging method based on continuous frequency-stabilized lasers. The source 2) is locked on the external stable atomic clock through the repetition frequency control module 3. At the same time, the continuous frequency stabilized laser and the double optical comb interaction module 5 combine the continuous laser generated by the continuous frequency stabilized laser generation module 4 with the two optical frequency comb seeds The output laser of the optical frequency comb source (namely optical frequency comb seed source 1 and optical frequency comb seed source 2) is used for beat frequency, and the electrical signal carrying the frequency instability of the optical comb is extracted, and the signal is subjected to RF signal power distribution and processing , a part of which is directly used to feedback control the characteristics of the laser resonator in the optical frequency comb seed source to stabilize the output carrier envelope phase frequency of the semiconductor laser LD, and the other part is used for periodic interference with the dual optical frequency comb optical imaging module 8 The signal is mixed to further offset the frequency drift of the dual optical frequency comb optical imaging module 8, so as to control the measurement accuracy of the entire dual optical frequency comb optical imaging module 8 from two aspects, and realize fast and ultra-high resolution optical imaging Comb coherent imaging.

As shown in Figure 1, the two optical frequency comb seed sources 1 and 2 are both pulsed laser sources pumped by semiconductor laser LD, and the laser resonator needs to have piezoelectric ceramic crystal PZT with adjustable cavity length and controllable dispersion Characteristics of electro-optical modulator EOM. The central wavelength of the laser output from the two optical frequency comb seed sources 1 and 2 is determined by the gain medium in the laser resonator, and the appropriate seed source system can be selected according to the basic optical response characteristics of the sample to be tested.

As shown in Figure 1, in order to meet the requirements of the system’s dual-comb coherent optical imaging, it is necessary to make the repetition frequency signals of the output pulses of the two optical frequency comb seed sources 1 and 2 have a small difference, which is generally in the range of 100 KHz to Hz order of magnitude.

As shown in Figure 1, the repetition frequency locking module 3 has two sets of independent phase-locked loop circuits that precisely lock the output repetition frequency signals of the two optical frequency comb seed sources 1 and 2 respectively. The detected repetition frequency signal of the optical comb is mixed with the standard signal triggered by the external atomic clock to obtain an error signal, which is amplified and fed back to control the piezoelectric ceramic crystal PZT in the optical comb seed source, thereby locking the cavity length of the laser resonator, thereby Control the stability of the output pulses of each optical frequency comb seed source 1 and 2 in the time domain.

As shown in Figure 1, the continuous frequency-stabilized laser generator module 4 provides a stable standard in the frequency domain for the entire dual optical comb system, and its output laser light is obtained by beating the output light of two optical frequency comb seed sources 1 and 2. Comb frequency drift information. In the actual measurement process, it is necessary to reasonably select the output wavelength of the continuous frequency stabilized laser and control its polarization state according to the output light characteristics of the optical frequency comb, so as to obtain a high signal-to-noise ratio radio frequency signal to control the entire imaging system. The continuous frequency stabilized laser here refers to the single longitudinal mode laser with a laser frequency linewidth in the order of Hz, and its generator (i.e. the continuous frequency stabilized laser generation module 4) generally consists of an ordinary continuous laser combined with a Fabry-Perot cavity (F-P cavity), and use the gain curve to form a laser frequency stabilization system with the transition center frequency of the atom itself as the reference frequency. At the same time, it is necessary to adopt measures such as constant temperature, expansion coefficient matching, shockproof, sealing, and stable power supply to carry out passive frequency stabilization of the laser to further ensure the frequency stability of the continuous laser, making it the frequency standard of the dual optical comb system.

As shown in Figure 1, the continuous frequency stabilized laser and dual optical comb interaction module 5 is the output laser of two optical frequency comb seed sources 1 and 2 and the three optical signals of the continuous frequency stabilized laser for coherent beat frequency, and obtains the carried An optoelectronic combination device for radio frequency signals with phase shift information of the carrier envelope of an optical frequency comb. It includes two sets of independent optical combs and optical components required for continuous laser beat frequency and electrical components required for beat frequency signal filtering and difference frequency. Its main function is to beat the output lasers of the two optical frequency comb seed sources 1 and 2 obtained by beam splitting with the continuous frequency-stabilized laser respectively, and filter the comb teeth and continuous The two beat frequency signals generated by the frequency-stabilized laser are mixed, and the obtained difference frequency signal f _- is used for power distribution and processing of radio frequency signals. Since the continuous frequency-stabilized laser provides a reliable frequency standard, and the repetition frequency of the two optical frequency comb seed sources 1 and 2 has been precisely controlled, the f _- signal obtained reflects the carrier envelope of the dual optical frequency comb system. The frequency instability caused by phase drift, that is, the carrier envelope phase drift frequency of the optical comb is transmitted in the form of radio frequency signals.

As shown in Figure 1, the radio frequency signal power distribution and processing module 6 is composed of an electronic power divider, and the bandwidth of the frequency divider needs to be reasonably selected according to the value of the radio frequency signal to meet the high-speed response of the system and suppress additional noise. In this method, the input radio frequency signal is divided into three paths.

As shown in Figure 1, among the three signals generated by the RF signal power distribution and processing module 6, one is used for feedback control of the pump lasers (i.e. semiconductor laser LD) of the two optical frequency comb seed sources 1 and 2, and the other is used for Feedback controls the electro-optic modulator EOM inside the two optical frequency comb seed sources 1 and 2, one of which is used to mix with the collected sample signal, and controls the frequency stability of the entire measurement device from multiple aspects.

As shown in Figure 1, since the frequency band of the radio frequency signal generated by the interaction between the optical frequency comb seed source and the continuous frequency-stabilized laser is not necessarily in the same frequency band as the interference spectrum signal generated by the optical frequency comb optical imaging module 8, it is necessary to use a frequency doubler to One of the signals obtained from the above power division is frequency-multiplied so that it can be mixed with the interference spectrum signal, which just offsets the frequency instability of the optical comb system.

As shown in Figure 1, the dual optical frequency comb optical imaging module 8 uses one path of light in the two optical frequency comb seed sources 1 and 2 as the detection light, and the other path of light as the reference light to detect the sample shape, which can be determined according to the detection method. Different detection devices with different construction structures can fully stimulate the optical information of the sample.

As shown in Figure 1, the sample data acquisition and processing module 9 includes components such as a balance detection device, a data acquisition card, and a weak signal analyzer, and extracts a large amount of data obtained during the point-by-point scanning of the sample to obtain an interference spectrum signal. The spectral signal is subjected to further noise processing to obtain the final spectral signal, and then the signal is restored to sample morphology information to realize dual-comb spectral imaging.

As shown in FIG. 1 , the computer 10 can cooperate with the program to complete the data processing process, and can visualize the imaging process through programming, so that the real-time monitoring of optical comb imaging can ensure the high-speed and effective operation of the system.

As shown in Figure 1, the specific steps of the dual optical frequency comb optical imaging method based on continuous frequency-stabilized laser in this embodiment are as follows:

First, the two optical frequency comb seed sources 1 and 2 are adjusted to be in a good self-starting mode-locking state, and their respective output lasers are divided into three beams, and a part of them enters the repetition frequency locking module 3 through the photodetector. The electronic servo feedback system of the phase loop precisely locks the repetition frequency signal of the optical comb on the external atomic clock, and the other part of the beam-split optical comb laser is used to interact with the continuous frequency-stabilized laser, and the last part of the beam-split optical comb laser is used to to generate optical comb imaging signals. The output frequencies of the two optical frequency comb seed sources 1 and 2 with a small repetition frequency difference are f _comb1 =nf _rep +f _ceo and f _comb2 =n(f _rep +Δf _rep )+f _ceo ^' respectively, where f _rep is the repetition frequency of the optical frequency comb seed source 1, Δfrep is the slight difference between the repetition frequency of the optical frequency comb seed source 2 and _the optical frequency comb seed source 1, f _ceo and f _ceo ^' are the unlocked optical frequencies frequency.

Secondly, the continuous frequency-stabilized laser and the output light of the two optical frequency comb seed sources 1 and 2 are coherently beat by the continuous frequency-stabilized laser and the dual-comb interaction module 5, and the comb teeth of the optical comb and the continuous laser at the same position are generated The two beat frequency signals with similar frequencies are filtered out to make the difference frequency, and the radio frequency signal f _- is obtained, which reflects the drift degree of the above f _ceo and f _ceo ^' , and converts the difficult-to-measure optical frequency into an easy-to-operate electrical frequency. The f _- signal is divided into three equal-value f ₁ , f ₂ and f ₃ signals by the radio frequency signal power distribution and processing module 6 to control the electro-optic modulator EOM in the cavity of the optical comb seed source, the current and imaging of the semiconductor laser LD The system detects the obtained sample spectral signal.

At the same time, another part of the output light from the optical frequency comb seed sources 1 and 2 enters the dual optical frequency comb optical imaging module 8 for sample detection, and reasonably controls the chirp characteristics, spectral coverage and spectral coverage of the optical frequency comb seed sources 1 and 2 output lasers. Factors such as peak power and polarization state fully excite the optical properties of the sample to be measured. Through the precise rotation of the mechanical scanning galvanometer or the sample stage, the point-by-point measurement process of the sample is completed, and the interference spectrum signal f _i of the sample is obtained.

Finally, the nf ₃ signal generated by the frequency multiplier 7 is mixed with the f _i signal to further offset the error caused by the carrier envelope phase frequency unlocked by the dual optical comb to the measurement, and the final signal f _signal is obtained for step-by-step Point restoration, through computer display, realizes fast and high-resolution optical imaging of the sample to be tested.

the

Embodiment 2: As shown in Figure 2, it is a schematic diagram of using a polarization rotation-locked mode all-fiber laser as an optical frequency comb seed source to perform scanning imaging of a dual-comb sample, and the specific steps are as follows:

(1) The two optical frequency comb seed sources 1 and 2 both adopt an all-fiber structure, use a 980nm semiconductor laser LD as a pump source, enter the laser cavity through a fiber wavelength division multiplexer 11, and single-mode ytterbium-doped The gain fiber 12 is used as the gain medium, the fiber isolator 13 ensures the one-way operation of the laser, the piezoelectric ceramic crystal PZT is wound on the single-mode fiber in the cavity, and the electro-optic modulator EOM adopts a fiber-optic phase and intensity modulator; The polarization controller 15 makes the laser reach a stable mode-locked state; the mode-locked pulse laser is output through the fiber coupler 14 .

(2) In the repetition frequency locking module 3, the optical comb repetition frequency signal detected by the photodetector is mixed with the standard signal triggered by the external atomic clock to obtain an error signal for amplification, and the feedback control optical frequency comb seed source 1, 2 piezoelectric ceramic crystal PZT, so as to lock the stability of the output pulse of each optical frequency comb seed source in the time domain.

(3) Based on the all-fiber characteristics of the optical frequency comb seed sources 1 and 2, the optical part of the continuous frequency-stabilized laser and the dual-comb interaction module 5 can also use an all-fiber type, and a reasonable selection of optical couplers and optical fiber bandpass filters center wavelength, so that the obtained beat frequency signal has a higher signal-to-noise ratio; the electrical part needs to select two bandpass filters with a passband bandwidth below ±10MHz to filter out two beat frequency signals with similar frequencies, and then The frequency is mixed by a mixer, and the difference frequency signal f _- is taken as the feedback control radio frequency signal of the system.

(4) Part of the output laser light of the two optical combs is converted into a spatial light through the collimator of the corresponding band, and the output light of the optical frequency comb seed source 1 is used as the detection light, and the output light of the optical frequency comb seed source 2 is As a reference light for dual-comb coherent imaging detection.

(5) The output light of the optical frequency comb seed source 1 first passes through an optical motor delay module 16 composed of a high reflection mirror. The function of this module is to adjust the process of the probe light from the output port to the sample to be tested and then to the detector The length of the spatial optical path taken by the middle and reference light, that is, to ensure that when reaching the balance detector in the sample data acquisition and processing module 9, the optical paths experienced by the two laser beams are consistent, so as to ensure that the signal light and the reference light can realize beat frequency.

(6) The output laser light of the optical frequency comb seed source 2 used as reference light is divided into two beams by the polarization beam splitter 17, one beam enters the sample together with the probe light through the dichroic mirror 18, and the other beam directly enters the detector, The reference laser can be used as a pump light source to excite the molecular transition of the sample during the imaging process, so that the nonlinear effect in the imaging process can be successfully completed. On the other hand, it can provide a unified standard for the obtained interference spectrum signal during the detection process and enhance the measurement. Consistency and credibility of results.

(7) The reference laser beam and probe laser beam combined by the dichroic mirror 18 are first incident on the scanning galvanometer 19, reflected by the total reflection mirror 20, and then passed through the microscope objective lens group 21 to pair the sample placed on the one-dimensional sample stage 22 Perform optical comb spectral imaging detection. Through the moving scanning of the scanning galvanometer 19, the construction of the x-axis and y-axis in the three-dimensional imaging diagram of the sample is obtained, and the depth measurement of the sample is performed through the optical frequency comb at each point, that is, the z-axis information in the three-dimensional imaging diagram is obtained.

(8) After passing through the sample, the laser light passes through the spatial bandpass filter 23 to filter out stray light irrelevant to the signal during the detection process and improve the signal-to-noise ratio of the interference spectrum signal.

(9) In the sample data acquisition and processing module 9, the optically filtered probe light and reference light are detected in balance, and the corresponding high-speed data acquisition card is used for data acquisition, and the obtained interference spectrum signal f _i is compared with the frequency multiplier 7. The generated radio frequency signal nf ₃ carrying the frequency jitter of the optical comb is mixed to further control the phase error of the optical comb system to obtain a signal f _signal with optical information of the sample. The restoration and presentation of the f _signal is completed by the computer 10, so as to realize high-resolution point-by-point double-comb spectral information measurement and sample optical imaging.

the

Embodiment three: as shown in Figure 3, a half-space half-fiber laser based on SESAM is used as an optical frequency comb seed source to perform a schematic diagram of dual-comb coherent anti-Stokes Raman scattering imaging, and the specific steps are as follows:

(1) The two optical frequency comb seed sources 1 and 2 both adopt an all-fiber structure, use a 980nm semiconductor laser LD as a pump source, enter the laser cavity through a fiber wavelength division multiplexer 11, and use a gain fiber 12 as a gain medium, the fiber isolator 13 ensures the one-way operation of the laser, and the piezoelectric ceramic crystal PZT is wound on the single-mode fiber in the cavity.

(2) Based on the half-space and half-fiber characteristics of the laser resonator, the intracavity polarization beam splitter 24 is used in conjunction with the intracavity half-wave plate 25, so that part of the laser output from the polarization beam splitter 24 is used as the optical frequency comb seed source 1, 2, the other part of the laser light passes through the free-space electro-optic modulator EOM, and then passes through the oblique pair, and then enters the semiconductor saturable absorbing mirror SESAM. short pulse. Reasonable selection of the semiconductor saturable absorber mirror SESAM response band and modulation depth enables the laser resonator to achieve a stable mode-locked state.

(3) Since the two optical frequency comb seed sources 1 and 2 are both in the state of spatial light output, the beam splitter of the corresponding wavelength band is used to split the optical comb light. For each optical frequency comb seed source, its output laser is divided into at least three beams, one beam is used to enter the repetition frequency locking module 3, and the other beam is used to enter the continuous frequency-stabilized laser and the dual optical comb interaction module 5 and The continuous frequency-stabilized lasers interact, and the other beam is used as an optical comb for imaging.

(4) In the repetition frequency locking module 3, the repetition frequency signal of the optical comb detected by the photodetector is mixed with the standard signal triggered by the external atomic clock, and the error signal is obtained for amplification, and the feedback controls the piezoelectricity in the optical comb seed source. The ceramic crystal PZT locks the stability of the output pulse of each optical frequency comb in the time domain.

(4) Based on the spatial light output characteristics of the optical comb seed source in this embodiment, the optical part of the continuous frequency-stabilized laser and the dual optical comb interaction module 5 can also adopt a spatial form, which includes beam combining sheets, gratings, and pinhole light Adjust the pitch angle of each component, so that the obtained beat frequency signal has a higher signal-to-noise ratio; the electrical part needs to select two band-pass filters with a passband bandwidth below ±10MHz The two beat frequency signals with similar frequencies are filtered out, and then mixed by a mixer, and the difference frequency signal f _- is taken as the feedback control radio frequency signal of the system.

(5) Broaden the spectral range of the output laser from the optical frequency comb seed source 1 through the photonic crystal fiber 27, reasonably control the polarization state, peak power, pulse width and other parameters of the laser input into the photonic crystal fiber, so that the output from the photonic crystal fiber 27 Lasers obtain a spectral range covering a wide range from the visible to the infrared. The femtosecond pulse laser pumps the photonic crystal fiber 27 to generate a supercontinuum laser output as a pump light source, which can realize broadband CARS spectral detection and microscopic imaging technology with a wide and simultaneous detection spectral range.

(6) Part of the laser beam split by the optical frequency comb seed source 1 and part of the laser beam split by the optical frequency comb seed source 2 are incident together for dual-comb coherent imaging detection. The two laser beams are combined by the dichroic mirror 18 in the space, and the light fields are overlapped in the space, and propagate in the same direction.

(7) After being reflected by the total reflection mirror 20, the two-way optical comb laser beams combined by the dichroic mirror 18 are first incident on the chirped mirror group 28, and the output laser light of the optical comb is further managed for dispersion, and the compensation is made by the laser resonator And the second-order dispersion and higher-order dispersion produced by the optical comb power amplifier and photonic crystal fiber, so that the laser can reach the output state of ultra-narrow pulse, which meets the requirements of high-resolution optical comb imaging.

(8) In the process of dual-comb coherent anti-Stokes Raman scattering imaging, the pump light and the Stokes light (probe light) formed by the difference between the frequency of the pump light and the Raman frequency shift of the sample The laser is frequency-mixed by combining the phase-matching technology, and the laser interacts with the medium through the third-order nonlinear susceptibility to generate an oscillation polarization with a frequency shift, and emits a coherent anti-Stokes Raman scattering signal. Therefore, the laser output from the chirped mirror 28 first passes through the spatial low-frequency filter 29 to filter out part of the laser light used for signal detection in the more complex spectral components of the optical frequency comb, and place it on the three-dimensional sample stage through the pair of microscope objective lenses 21 The sample on 30 is detected, and the laser light passing through the sample passes through the spatial high-frequency filter 31 to obtain the coherent anti-Stokes Raman scattering signal shifted up in frequency to be detected.

(9) During the dual-comb optical imaging process, the three-dimensional space movement of the three-dimensional sample stage 30 is used to complete the point-by-point scanning of the sample, and all the anti-Stokes radiation generated by four-wave mixing is used during the entire sample scanning process. The intensities are superimposed to form the interference spectrum signal f _i .

(10) In the sample data acquisition and processing module 9, the above-mentioned periodic interference signal f _i is collected through the corresponding high-speed data acquisition card, and the radio frequency signal nf carrying the frequency jitter of the optical comb generated by the frequency multiplier 7 ₃ Do frequency mixing to further control the phase error of the optical comb system to obtain a signal f _signal with optical information of the sample. The restoration and presentation of the f _signal is completed by the computer 10, so as to realize point-by-point double-comb coherent anti-Stokes Raman scattering imaging. The method in this embodiment can not only be used to obtain high-resolution molecular vibrational spectroscopy and imaging, but also can be used to test the temperature and concentration of samples.

Claims (5)

1. the two optical frequency com optical imaging methods based on continuous Frequency Stabilized Lasers, relate to two optical frequency com seed sources, it is characterized in that described optical imaging method comprises the steps: two described optical frequency com seed sources Output of laser to be separately divided into three tunnels;

The first via, the Output of laser of two described optical frequency com seed sources enter respectively frequency control module with by the repetition frequency semaphore lock of described optical frequency com seed source on extraneous atomic clock;

Second tunnel, the Output of laser of two described optical frequency com seed sources and the Output of laser of continuous Frequency Stabilized Lasers generation module are combed in interaction module at continuous sharp Frequency Stabilized Lasers and two light and are carried out beat frequency, produce the close beat signal of two frequencies and leaching out does difference frequency, obtain radiofrequency signal f _- ; Distributed described radiofrequency signal with processing module by RF signal power f _- be divided into three equivalent road signals f ₁ , f ₂ with f ₃ signal, wherein said signal f ₁ with f ₂ feed back to the electrooptic modulator in two described optical frequency com seed sources and semiconductor laser respectively, to stablize the carrier envelope phase frequency of two described optical frequency com seed source Output of lasers, described signal f ₃ signal is enlarged into through frequency multiplier nf ₃ after enter sample data Acquire and process module;

3rd tunnel, is incident to testing sample using the Output of laser of wherein optical frequency com seed source described in First as detection light, using the Output of laser of wherein second described optical frequency com seed source as with reference to light with described detection photo-beat frequency to obtain interference spectum signal f _i ; Described interference spectum signal f _i enter afterwards in described sample data Acquire and process module with described signal nf ₃ carry out mixing to offset frequency instability, obtain spectral signal f _signal , and to described spectral signal f _signal carry out pointwise reduction, realize the optical imagery of described testing sample.

2. a kind of two optical frequency com optical imaging methods based on continuous Frequency Stabilized Lasers according to claim 1, is characterized in that the Output of laser frequency of two described optical frequency com seed sources is respectively f _comb1 =nf _rep + f _ceo with f _comb2 =n (f _rep + Δ f _rep )+f _ceo ^' , wherein f _rep it is the repetition frequency of optical frequency com seed source described in First, Δ f _rep the small difference of the repetition frequency of optical frequency com seed source described in second described optical frequency com seed source and First, f _ceo with f _ceo ^' represent the carrier envelope phase drift frequency of optical frequency com seed source and second described optical frequency com seed source described in First respectively.

3. a kind of two optical frequency com optical imaging methods based on continuous Frequency Stabilized Lasers according to claim 1, is characterized in that the Output of laser of described continuous Frequency Stabilized Lasers generation module refers to the single longitudinal mode laser of laser frequency live width in Hz magnitude.

4. a kind of two optical frequency com optical imaging methods based on continuous Frequency Stabilized Lasers according to claim 1, is characterized in that being provided with electrooptic modulator and semiconductor laser in the laserresonator in described optical frequency com seed source; Described signal f ₁ act on described electrooptic modulator after being converted to DC voltage, change the refractive index of described electrooptic modulator to adjust the chirp value of described laserresonator and to compensate the long amount of mismatch in its chamber; Described signal f ₂ feed back to described semiconductor laser, the electric current of semiconductor laser described in FEEDBACK CONTROL is with the noisiness of firm described laserresonator.

5. a kind of two optical frequency com optical imaging methods based on continuous Frequency Stabilized Lasers according to claim 1, is characterized in that the frequency of described detection light is f _comb1 =nf _rep + f _ceo , the frequency of described reference light is f _comb2 =n (f _rep + Δ f _rep )+f _ceo ^' , obtain after described detection light and described reference light carry out beat frequency being spaced apart Δ f by a series of _rep radiofrequency signal composition described interference spectum signal f _i .