CN114624981B - Ultra-fast holographic microscopic imaging method and system based on time broadening - Google Patents

Abstract

The invention discloses an ultrafast holographic microscopic imaging method and system based on time broadening. The system includes: an ultrashort pulse sequence generation module for generating multi-wavelength chirped pulse sequences for illumination; a holographic imaging spectrometer, A spatially discrete multi-wavelength off-axis hologram sequence is generated based on a multi-wavelength chirped pulse sequence; a hologram reconstruction module is used to reconstruct the multi-wavelength off-axis hologram sequence to obtain a quantitative optical thickness sequence of the sample. This invention reconstructs the multi-wavelength hologram sequence generated by the holographic imaging spectrometer to obtain the phase sequence, and then uses each sub-pulse wavelength of the multi-wavelength chirped pulse sequence as a standard to obtain a quantitative sample optical thickness sequence, which can be used in a single exposure. Realizing three-dimensional spatial imaging with ultra-short time resolution and ultra-fast imaging speed solves the problem that existing methods can only obtain two-dimensional spatial information of the detection target, and greatly improves the imaging effect.

Description

An ultrafast holographic microscopy imaging method and system based on time broadening

Technical field

The invention belongs to the field of ultrafast optical imaging, and specifically relates to an ultrafast holographic microscopic imaging method and system based on time broadening.

Background technique

Optical imaging that achieves ultra-short time resolution and ultra-fast imaging speed has always been an important research direction in the field of optical imaging. The time resolution imaging speed of existing detectors, such as charge-coupled devices (CCD) and complementary metal-oxide semiconductor (CMOS) cameras, can only reach sub-microsecond levels. It is difficult to detect transients using traditional optical architectures and light sources. , non-repetitive phenomena are detected.

Frequency-space-time mapping ultrafast imaging based on spatial broadening is an all-optical ultrafast imaging technology with a resolution of picosecond/subpicosecond level. However, the existing frequency-space-time mapping ultrafast imaging device is complicated , the construction cost is high, and it can only obtain the two-dimensional spatial information of the detection target, but cannot detect the phase/depth information of the target. Therefore, it is very urgent to realize higher-dimensional ultrafast imaging technology.

Contents of the invention

Purpose of the invention: In order to overcome the deficiencies in the existing technology, provide an ultrafast holographic microscopy imaging method and system based on time broadening, which can achieve ultra-short time resolution and ultra-fast imaging in a single exposure. Three-dimensional spatial imaging of velocity.

Technical solution: In order to achieve the above objectives, the present invention provides an ultrafast holographic microscopy imaging system based on time broadening, including:

Ultrashort pulse sequence generation module, used to generate multi-wavelength chirped pulse sequences for illumination;

Holographic imaging spectrometer, used to generate spatially discrete multi-wavelength off-axis hologram sequences based on multi-wavelength chirped pulse sequences;

The hologram reconstruction module is used to reconstruct a multi-wavelength off-axis hologram sequence to obtain a quantitative optical thickness sequence of the sample.

Further, the ultrashort pulse sequence generation module includes an ultrashort pulse laser, a first diffraction grating, a second diffraction grating, a first convex lens, a second convex lens, a digital micro-mirror device and a glass rod;

The first diffraction grating is used to disperse the pulses generated by the ultrashort pulse laser;

The first convex lens is used to collimate the dispersed pulses into one-dimensional spectral lines on the digital micro-mirror device;

The digital micro-mirror device is used to selectively filter one-dimensional spectral lines and reflect them to the second convex lens;

The second convex lens and the second diffraction grating are used to combine the filtered pulses into parallel light pulses;

The glass rod is used for time domain broadening of parallel light pulses.

Further, the holographic imaging spectrometer includes a third convex lens, an imaging lens, a beam splitter, a first microscopic objective lens, a second microscopic objective lens, a first reflective mirror, a second reflective mirror, a third reflective mirror, and a third diffraction grating. , CCD camera;

The third convex lens is used to converge the pulse sequence generated by the ultrashort pulse sequence generation module;

The spectroscope is used to separate the converged pulse sequence into object light and reference light;

The first microscope objective is used to project object light onto the sample and collect scattered light from the sample and return it to the spectroscope;

The second microscope objective is used to project the reference light to the first reflector, and collect the reference light reflected by the first reflector to the spectroscope;

The first reflector is used to reflect the reference light to the second microscope objective;

The second reflector and the third reflector are used to reflect the parallel propagating object light and reference light before incident on the third diffraction grating;

The imaging lens is used to project the sub-pulse objects and reference light emitted by the third diffraction grating to different positions on the CCD camera;

The CCD camera is used to capture discrete multi-wavelength off-axis hologram sequences.

Further, the first reflector is placed obliquely, and the inclination direction is orthogonal to the dispersion direction of the third diffraction grating, so that the reference light on the imaging surface can be obliquely incident and interfere with the object light to form an off-axis hologram and reduce dispersion. Effect on visibility of hologram interference fringes.

An ultrafast holographic microscopy imaging method based on time broadening, including the following steps:

S1: Generate multi-wavelength chirped pulse sequences through the ultrashort pulse sequence generation module;

S2: The holographic imaging spectrometer uses a multi-wavelength chirped pulse sequence for illumination to produce a spatially discrete multi-wavelength off-axis hologram sequence;

S3: Use the hologram reconstruction module to reconstruct the multi-wavelength off-axis hologram sequence to obtain a quantitative optical thickness sequence to achieve three-dimensional holographic microscopic imaging.

Further, the generation process of the multi-wavelength chirped pulse sequence in step S1 is:

The ultrashort pulse laser emits a parallel light pulse, which is dispersed by the first diffraction grating and collimated into a one-dimensional spectral line by the first convex lens on the digital micro-mirror device on its back focal plane. The digital micro-mirror device is loaded with In the binary image, the one-dimensional spectral lines are selectively filtered. The filtered pulses pass through the second convex lens and the second diffraction grating and then are combined into parallel light pulses. The glass rod broadens the parallel light pulses in the time domain to form multiple Wavelength chirped pulse sequence.

Further, the generation process of the multi-wavelength off-axis hologram sequence in step S2 is:

The pulse sequence is condensed by the third convex lens and then divided into object light and reference light by the spectroscope. The object light passes through the first microscope objective lens and is projected on the sample on its front focal plane. The scattered light of the sample is re-collected by the first microscope objective lens. Return to spectroscope;

The reference light passes through the second microscopic objective lens and is projected on the inclined first reflecting mirror on its back focal plane. After the reference light is reflected by the first reflecting mirror, it is collected by the second microscopic objective lens and then returns to the spectroscope;

Due to the action of the spectroscope, the returned object light propagates in parallel with the reference light, is reflected by the second mirror and the third mirror in turn, and then enters the third diffraction grating. After passing through the third diffraction grating, it has different wavelengths - The time-mapped sub-pulse objects and reference light are separated in the x-direction, and are projected and converged at different positions on the CCD camera on its back focal plane through the imaging lens. The sub-pulse objects and reference light with the same wavelength-time mapping are separated at a certain The angle projection interferes at the same position on the CCD camera to form an off-axis hologram. The CCD camera captures a series of discrete off-axis holograms within one exposure time, and obtains a multi-wavelength off-axis hologram sequence.

Further, in step S3, a hologram reconstruction algorithm is used to reconstruct the off-axis hologram:

The corresponding sub-pulse wavelength is λ _i , and the hologram is expressed as g(x,y)=a(x,y)+c(x,y)exp(j2πf _y x)+c ^* (x,y)exp( -j2πf _y x), where a is the DC component, b is the degree of modulation,/> is the phase, ^* represents complex conjugation, f _y is the hologram fringe spatial frequency;

Perform Fourier transform on g to get G(u,v)=A(u,v)+C(uf _x ,v)+C ^* (u+f _x ,v), where A, C, C ^* are respectively For the Fourier transform of a, c, c ^* , use a low-pass filter to filter out C(uf _x , v) and move it to the origin of the frequency domain to get C, perform an inverse Fourier transform on it to get c, and calculate the phase for imag represents the imaginary part, and real represents the real part. After two-dimensional unwrapping of the phase, the optical thickness of the sample is calculated as:/>

Beneficial effects: Compared with the existing technology, the present invention reconstructs the multi-wavelength hologram sequence generated by the holographic imaging spectrometer to obtain the phase sequence, and then uses the wavelength of each sub-pulse of the multi-wavelength chirped pulse sequence as the standard to obtain the quantitative optical thickness of the sample. The sequence can achieve three-dimensional spatial imaging with ultra-short time resolution and ultra-fast imaging speed in a single exposure. It solves the problem that existing methods can only obtain two-dimensional spatial information of the detection target, and greatly improves the imaging effect.

Description of the drawings

Figure 1 is a schematic diagram of the ultrafast holographic microscopy imaging system based on time broadening provided by the present invention;

Figure 2 is a frequency domain characteristic diagram of the multi-wavelength chirped pulse virtual sequence generated by the ultrashort pulse sequence generation module in this embodiment;

Figure 3 is a timing characteristic diagram of the multi-wavelength chirped pulse virtual sequence generated by the ultra-short pulse sequence generation module in this embodiment;

Figure 4 shows 10 spatially discrete off-axis holograms collected by the camera under one exposure in this embodiment;

Figure 5 is a three-dimensional image sequence diagram reconstructed using the hologram reconstruction algorithm in this embodiment.

In Figure 1, 1 is an ultrashort pulse sequence generation module, 2 is a holographic imaging spectrometer, 101 is an ultrashort pulse laser, 102 is a first diffraction grating, 106 is a second diffraction grating, 209 is a third diffraction grating, 103 is The first convex lens, 105 is the second convex lens, 107 is the glass rod, 104 is the digital micro-mirror device, 201 is the third convex lens, 210 is the imaging lens, 202 is the beam splitter, 203 is the first microscopic objective lens, and 205 is the third convex lens. Two microscope objectives, 204 is the sample, 206 is the first reflector, 207 is the second reflector, 208 is the third reflector, 211 is the CCD camera, and 212 is the computer.

Detailed ways

The present invention will be further clarified below in conjunction with the accompanying drawings and specific examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. After reading the present invention, those skilled in the art will be familiar with various aspects of the present invention. Modifications in the form of equivalents fall within the scope defined by the appended claims of this application.

The invention provides an ultrafast holographic microscopy imaging system based on time broadening, as shown in Figure 1, which includes: an ultrashort pulse sequence generation module 1, a holographic imaging spectrometer 2 and a hologram reconstruction module.

The ultrashort pulse sequence generation module 1 includes an ultrashort pulse laser 101, a first diffraction grating 102, a second diffraction grating 106, a first convex lens 103, a second convex lens 105, a digital micromirror device 104 and a glass rod 107.

The holographic imaging spectrometer 2 includes a third convex lens 201, an imaging lens 210, a beam splitter 202, a first microscopic objective lens 203, a second microscopic objective lens 205, a first reflective mirror 206, a second reflective mirror 207, a third reflective mirror 208, Third diffraction grating 209 and CCD camera 211. The first reflecting mirror 206 is placed tilted around the x-axis, and the tilting direction is orthogonal to the dispersion direction of the third diffraction grating 209 .

The hologram reconstruction module is installed in the computer 212 and is specifically a hologram reconstruction system.

In this embodiment, the above-mentioned holographic microscopy imaging system is used to perform three-dimensional holographic microscopy imaging on sample 204 to provide an ultra-fast holographic microscopy imaging method based on time broadening. Sample 204 is specifically a reflector coated with NJNU relief. Figure 1, the specific imaging method is:

S1: Generate multi-wavelength chirped pulse sequence through ultrashort pulse sequence generation module 1:

The ultrashort pulse laser 101 emits a parallel light pulse with a center wavelength of 800nm, a 3dB bandwidth of 100nm, and a pulse width of 5.5ps. The pulse is dispersed by the first diffraction grating 102 and passes through the digital micro-reflector of the first convex lens 103 on its back focal plane. The one-dimensional spectral lines are collimated on the device 104. By loading a binary image on the digital micro-mirror device 104, the one-dimensional spectral lines are selectively filtered. The filtered pulses pass through the second convex lens 105 and the second diffraction grating 106 and then are combined. The beam becomes a parallel light pulse again, and the glass rod 107 broadens the parallel light pulse in the time domain to form a multi-wavelength chirped pulse sequence.

In this embodiment, the first diffraction grating 102 and the second diffraction grating 106 have 600 lines/mm, the focal length of the first convex lens 103 and the second convex lens 105 is 100 mm, and the glass rod 107 is made of N-SF10 material with a length of 3 m.

As shown in Figure 2, there are 10 one-dimensional spectral lines after filtering, which are 750nm, 760nm, 770nm, 780nm, 790nm, 800nm, 810nm, 820nm, 830nm, 840nm. The width of each spectral line is 0.25 nm; as shown in Figure 3, the multi-wavelength chirped pulse sequence formed after time domain broadening has a total of 10 sub-pulses, each sub-pulse has a pulse width of 5.3ps, and the interval between adjacent pulses is 10ps.

S2: Holographic imaging spectrometer 2 uses a multi-wavelength chirped pulse sequence for illumination to produce a spatially discrete multi-wavelength off-axis hologram sequence:

The multi-wavelength chirped pulse sequence is condensed by the third convex lens 201 and then divided into object light and reference light by the spectroscope 202. The object light passes through the first microscope objective lens 203 and is projected on the sample 204 on its front focal plane. The scattered light of the sample 204 It is collected again by the first microscope objective lens 203 and returned to the spectroscope 202;

The reference light passes through the second microscopic objective lens 205 and is projected on the inclined first reflecting mirror 206 on its back focal plane. After the reference light is reflected by the first reflecting mirror 206, it is collected by the second microscopic objective lens 205 and then returns to the spectroscope. 202;

Due to the action of the spectroscope 202, the returned object light propagates in parallel with the reference light, is reflected by the second reflecting mirror 207 and the third reflecting mirror 208 in turn, and then enters the third diffraction grating 209. After passing through the third diffraction grating 209 , the sub-pulse object and reference light with different wavelength-time mapping are separated in the x direction, and are projected and converged on the CCD camera 211 on its rear focal plane through the imaging lens 210. The sub-pulses with the same wavelength-time mapping are The object and reference light are projected at the same position on the CCD camera 211 at a certain angle and interfere to form an off-axis hologram. The CCD camera 211 captures a series of discrete off-axis holograms within one exposure time, and obtains multi-wavelength holograms. Axis hologram sequence.

In this embodiment, the focal length of the third convex lens 201 is 200mm, and the focal length of the imaging lens 210 is 150mm; the specifications of the first microscopic objective lens 203 and the first reflector 206 are a focal length of 40mm, NA=0.26; the third diffraction grating 209 is 600 Graduation line/mm; CCD camera 211 specifications are pixel size 3um, pixel number 5000×1500; each hologram imaging field of view is 200um×200um. The first reflecting mirror 206 is placed on the front focal plane of the second microscopic objective lens 205 , and the CCD camera 211 is placed on the rear focal plane of the imaging lens 210 .

In this embodiment, 10 off-axis hologram sequences are captured, as shown in Figure 4.

S3: Reconstruct the multi-wavelength off-axis hologram sequence through the hologram reconstruction module to obtain a quantitative optical thickness sequence to achieve three-dimensional holographic microscopy imaging:

Use the hologram reconstruction algorithm to reconstruct 10 off-axis holograms:

Taking one of the 10 holograms as an example, the corresponding sub-pulse wavelength is λ _i , and the hologram is expressed as g(x,y)=a(x,y)+c(x,y)exp(j2πf _y x )+c ^* (x,y)exp(-j2πf _y x), where a is the DC component, b is the degree of modulation,/> is the phase, ^* represents complex conjugation, f _y is the hologram fringe spatial frequency;

Perform Fourier transform on g to get G(u,v)=A(u,v)+C(uf _x ,v)+C ^* (u+f _x ,v), where A, C, C ^* are respectively For the Fourier transform of a, c, c ^* , use a low-pass filter to filter out C(uf _x , v) and move it to the origin of the frequency domain to get C, perform an inverse Fourier transform on it to get c, and calculate the phase for imag represents the imaginary part, and real represents the real part. After two-dimensional unwrapping of the phase, the optical thickness of the sample is calculated as:/>

Finally, the three-dimensional image sequence diagram shown in Figure 5 is obtained.

In this embodiment, the solution adopted by the imaging system provided by the present invention has a final imaging speed of 6.8×1010 frames/second, a temporal resolution of 5.4ps, a field of view of each frame of 200 microns×200 microns, and a spatial resolution of 4.38 microns. It is superior to existing imaging systems in every aspect.

Claims (3)

1. An ultrafast holographic microscopy imaging system based on temporal broadening, comprising:

the ultra-short pulse sequence generating module is used for generating a multi-wavelength chirped pulse sequence for illumination;

the holographic imaging spectrometer is used for generating a spatially discrete multi-wavelength off-axis hologram sequence according to the multi-wavelength chirped pulse sequence;

a hologram reconstruction module for reconstructing the multi-wavelength off-axis hologram sequence to obtain a quantitative optical thickness sequence of the sample;

the ultra-short pulse sequence generating module comprises an ultra-short pulse laser, a first diffraction grating, a second diffraction grating, a first convex lens, a second convex lens, a digital micro-mirror device and a glass rod;

the first diffraction grating is used for dispersing pulses generated by the ultra-short pulse laser;

the first convex lens is used for collimating the dispersed pulse into a one-dimensional spectral line on the digital micro-mirror device;

the digital micro-mirror device is used for carrying out selective filtering on the one-dimensional spectral line and reflecting the one-dimensional spectral line to the second convex lens;

the second convex lens and the second diffraction grating are used for combining the filtered pulse into a parallel light pulse;

the glass rod is used for carrying out time domain broadening on the parallel light pulses;

the holographic imaging spectrometer comprises a third convex lens, an imaging lens, a spectroscope, a first micro objective, a second micro objective, a first reflecting mirror, a second reflecting mirror, a third diffraction grating and a CCD camera;

the third convex lens is used for converging the pulse sequences generated by the ultra-short pulse sequence generating module;

the spectroscope is used for dividing the converged pulse sequence into object light and reference light;

the first microscope objective is used for projecting object light on the sample, and collecting scattered light of the sample and returning the scattered light to the spectroscope;

the second microscope objective is used for projecting the reference light to the first reflecting mirror and collecting the reference light reflected by the first reflecting mirror to the spectroscope;

the first reflecting mirror is used for reflecting the reference light to the second micro objective lens;

the second reflector and the third reflector are used for reflecting the object light and the reference light which are transmitted in parallel and then making the object light and the reference light incident to the third diffraction grating;

the imaging lens is used for projecting the sub-pulse objects and the reference light emitted by the third diffraction grating to different positions on the CCD camera;

the CCD camera is used to capture discrete multi-wavelength off-axis hologram sequences.

2. The time-broadening-based ultrafast holographic microscopic imaging system of claim 1, wherein the first mirror is tilted and the tilt direction is orthogonal to the third diffraction grating dispersion direction.

3. An ultrafast holographic microscopic imaging method based on time broadening is characterized by comprising the following steps:

s1: generating a multi-wavelength chirped pulse sequence through an ultrashort pulse sequence generating module;

s2: the holographic imaging spectrometer uses the multi-wavelength chirped pulse sequence to illuminate, and generates a spatially discrete multi-wavelength off-axis hologram sequence;

s3: reconstructing the multi-wavelength off-axis hologram sequence through a hologram reconstruction module to obtain a quantitative optical thickness sequence, and realizing three-dimensional holographic microscopic imaging;

the generating process of the multi-wavelength chirped pulse sequence in the step S1 is as follows:

the ultra-short pulse laser emits parallel light pulses, the pulses are dispersed through a first diffraction grating, collimated into one-dimensional spectral lines on a digital micro-mirror device of a back focal plane through a first convex lens, the digital micro-mirror device is loaded with a binary image to selectively filter the one-dimensional spectral lines, the filtered pulses are combined through a second convex lens and a second diffraction grating and then become parallel light pulses again, and a glass rod expands the time domain of the parallel light pulses to form a multi-wavelength chirped pulse sequence;

the generating process of the multi-wavelength off-axis hologram sequence in the step S2 is as follows:

the pulse sequence is converged by the third convex lens and then is separated into object light and reference light by the spectroscope, the object light is projected on a sample on the front focal plane of the object light after passing through the first microscope objective, and scattered light of the sample is collected again by the first microscope objective and returns to the spectroscope;

the reference light is projected on the inclined first reflecting mirror on the rear focal surface of the second microscope objective lens, and the reference light is reflected by the first reflecting mirror, collected by the second microscope objective lens and returned to the spectroscope;

due to the effect of the spectroscope, returned object light and reference light are transmitted in parallel, reflected by the second reflector and the third reflector and then are injected into the third diffraction grating, sub-pulse objects with different wavelength-time mapping and reference light are separated in the x direction and projected on different positions of a CCD camera on the rear focal plane of the CCD camera through the imaging lens, the sub-pulse objects with the same wavelength-time mapping and the reference light are projected on the same position of the CCD camera at a certain included angle to interfere to form off-axis holograms, and the CCD camera captures a series of discrete off-axis holograms in one exposure time to obtain a multi-wavelength off-axis hologram sequence;

reconstructing an off-axis hologram using a hologram reconstruction algorithm in the step S3:

the corresponding sub-pulse wavelength is lambda _i The hologram is expressed as g (x, y) =a (x, y) +c (x, y) exp (j 2 pi f) _y x)+c ^* (x,y)exp(-j2πf _y x), wherein a is a direct current component,b is modulation degree, & gt>In order to be a phase of the light, ^* representing complex conjugate, f _y Spatial frequencies for hologram fringes;

fourier transforming G to obtain G (u, v) =a (u, v) +c (u-f) _x ,v)+C ^* (u+f _x V) wherein A, C ^* A, c respectively ^* Is a fourier transform of (C) using a low pass filter _x V) filtering and moving to the origin of frequency domain to obtain C, performing inverse Fourier transform to obtain C, and calculating the phase asimag represents the imaginary part, real represents the real part, and the optical thickness of the sample is calculated after two-dimensional unwrapping the phase: />