Two-dimensional Scanning Laser Imaging System Based on Spectral Angle Enhancement and Time Delay

Abstract

The present invention provides a two-dimensional scanning laser imaging system based on spectral angle enhancement and time delay, comprising an incident laser module, a diffraction grating, a first lens, a spectroscope, a second lens, a spectral time delay, an optical system, an arbitrary waveform generator, an acousto-optic modulator, a sample to be measured, and a data acquisition and processing unit. The present invention utilizes the wavelength-independent dispersion effect to introduce group velocity dispersion in free space and introduces 1ns nm in the visible light band. ‑1 The GVD introduces only 4-7dB of loss, which improves both system resolution and imaging clarity, enabling high-definition, accurate imaging. By combining an acousto-optic modulator with an arbitrary waveform generator, the system uses radio frequency signals to modulate the piezoelectric transducer to excite acoustic waves, which in turn influence the crystal inside, changing the crystal's refractive index and, consequently, the angle of the emitted light. This upgrades one-dimensional scanning to two-dimensional scanning, increasing the imaging dimension and enabling the acquisition of more image information.

Description

Technical Field

[0001] The present invention relates to the field of high-speed dynamic imaging, and in particular to a two-dimensional scanning laser imaging system based on spectral angle enhancement and time delay. Background Art

[0002] High-speed dynamic time-lapse imaging plays an extremely important role in fields such as cancer biology (Hoppe, P., Coutu, D. & Schroeder, T. Single-cell technologies sharpen up mammalian stem cell research. Nat. Cell Biol. 16, 919–927 (2014)) and regenerative medicine (Fritzsch FS, Dusny C, Frick O, Schmid A. Single-cell analysis in biotechnology, systems biology, and biocatalysis. Annual Review of Chemical and Biomolecular Engineering 3, 129-155 (2012)). However, traditional dynamic imaging has problems such as insufficient scanning speed and low transmittance. Galvanometer scanning mirror imaging can only reach a scanning rate of 10 kHz (Marshall GF, Stutz GE. Handbook of Optical and Laser Scanning, 2nd edn. Boca Raton: CRC Press (2011).), and rotating polygon mirror imaging can only reach a scanning rate of 100 kHz (Choi S, Kim P, Boutilier R, Kim MY, Lee YJ et al. Development of a high speed laser scanning confocal microscope with an acquisition rate upto 200 frames per second. Opt. Express 21, 23611–23618 (2013).). The spectral angle enhancement and time delay imaging technologies developed later can achieve high-speed dynamic imaging at ultrafast frequencies in the MHz range (Lau AKS, Wong TTW, Ho KKY, Tang MTH, Chan ACS et al. Interferometric time-stretch microscopy for ultrafast quantitative cellular and tissue imaging at 1μm.J Biomed. Opt. 19, 076001(2014).), but the imaging spatial resolution is not high.

[0003] If you want to improve the spatial resolution of imaging, you need to use time-delay imaging technology and use a medium with high dispersion (>1ns nm -1 Time-delay imaging in the visible light band plays a significant role in basic biology and biomedical diagnostics (Fritzsch FSO, Dusny C, Frick O, Schmid A. Single-cell analysis in biotechnology, systems biology, and biocatalysis. Annu. Rev. Chem. Biomol. Eng 3, 129–155 (2012).). However, in the visible light band, introducing group velocity dispersion using optical fibers is accompanied by extremely high optical losses (>50dB), which cannot meet people's application needs. Summary of the Invention

[0004] The problem to be solved by the present invention is to realize a method and system for two-dimensional laser scanning based on spectral angle enhancement and time delay, and to introduce group velocity dispersion in free space by utilizing the wavelength-independent dispersion effect, and to introduce 1ns nm in the visible light band (taking 700nm as an example). -1 The GVD only introduces a loss of 4 to 7 dB, which improves the system resolution while improving the imaging clarity, achieving high-definition and accurate imaging effects. This system uses an acousto-optic modulator combined with an arbitrary waveform generator, and uses radio frequency signals to modulate the piezoelectric converter to excite sound waves, and exert an influence on the internal crystal to change the refractive index of the crystal, thereby changing the angle of the outgoing light, upgrading the one-dimensional scan to a two-dimensional scan, improving the imaging dimension, and obtaining more image information.

[0005] The present invention is achieved through at least one of the following technical solutions.

[0006] A two-dimensional scanning laser imaging system based on spectral angle enhancement and time delay, comprising an incident laser module, a diffraction grating, a first lens, a beam splitter, a second lens, a spectral time delay, an optical system, an arbitrary waveform generator, an acousto-optic modulator, a sample to be measured, and a data acquisition and processing component;

[0007] The incident laser module is used to generate pulsed laser;

[0008] The diffraction grating is used to split the incident pulse laser spectrum, and the incident pulse laser is emitted at a solid cone angle θ;

[0009] The first lens is used to collimate the pulsed laser and prevent beam expansion;

[0010] The incident pulse laser passes through the beam splitter and is incident on the spectrum time delay device to form return light, and the return light is then reflected by the beam splitter and coupled into the optical system composed of the tube lens and the objective lens;

[0011] The second lens is used to focus the pulsed laser and input it into the spectral time delay device;

[0012] The optical system is used to correct the aberration of the system and collimate;

[0013] The arbitrary waveform generator is connected to the acousto-optic modulator. The arbitrary waveform generator applies a periodic radio frequency signal to the acousto-optic modulator, which can periodically change the angle of the emitted light, generate a plurality of sub-beams of light, and transform the M beams of one-dimensional scanning light into two-dimensional scanning light, which is then incident on the sample to be tested;

[0014] After scanning the sample to be measured, the two-dimensional scanning light is incident on the data acquisition and processing component to obtain image information of the sample to be measured.

[0015] Furthermore, the wavelength window of the incident laser module is 400-800 nm.

[0016] Furthermore, the incident laser module is a high repetition rate pulse laser.

[0017] Furthermore, the optical system includes a tube lens and an objective lens, wherein the tube lens is used to correct aberrations; and the objective lens is used to collimate the return light and form a one-dimensional scanning light.

[0018] Furthermore, the spectral time delay device includes two non-parallel mirrors for creating a spatial chirped path and introducing group velocity dispersion to the pulsed laser in free space.

[0019] Furthermore, the two reflectors form an offset angle α and satisfy 0<α<5 mrad, and the reflectivity of the two reflectors is >99.5%.

[0020] Furthermore, the data acquisition and processing component includes a high-speed photodetector, a real-time oscilloscope connected to the high-speed photodetector, and a computer. The high-speed photodetector is used to convert the output optical signal into an electrical signal, the real-time oscilloscope is used to reconstruct the collected signal to obtain the original image of the sample to be tested, and the computer is used to perform data processing and analysis to obtain high-speed, clear and accurate imaging.

[0021] The present invention also provides a corresponding two-dimensional scanning laser imaging method based on spectral angle enhancement and time delay. The method comprises the following steps:

[0022] The pulsed laser generated by the incident laser module passes through the diffraction grating, which splits the pulsed laser into a spectrum with a three-dimensional cone angle θ. The split pulsed laser is collimated by the first lens;

[0023] The collimated pulsed laser passes through the beam splitter, is focused by the second lens, and is incident on the spectral time delay device to introduce group velocity dispersion;

[0024] After the introduction of group velocity dispersion, M beams of pulsed laser light will return to the incident point along the incident light path, and will be reflected into the optical system through the beam splitter. The returning light will form a one-dimensional scanning light through the optical system.

[0025] An arbitrary waveform generator generates a radio frequency signal and sends it to the acousto-optic modulator. The piezoelectric converter inside the acousto-optic modulator will excite the sound wave and exert an influence on the internal crystal, changing the refractive index of the crystal. Using the arbitrary waveform generator to apply a periodic radio frequency signal to the acousto-optic modulator can periodically change the angle of the output light, generating several beamlets, and transforming the M beams of one-dimensional scanning light into two-dimensional scanning light, which is then incident on the sample to be tested.

[0026] After the two-dimensional scanning light scans the sample to be tested, the image information of the sample to be tested is obtained through the data acquisition and processing components.

[0027] Furthermore, the optical system includes a barrel lens and an objective lens. The return light first passes through the barrel lens in the optical system to correct aberrations, and then passes through the objective lens to be collimated to ultimately form a one-dimensional scanning light.

[0028] Furthermore, the spectral time delay device (6) includes two non-parallel mirrors with a reflectivity greater than 99.5%, which are used to create a spatial chirped path and introduce group velocity dispersion to the pulsed laser in free space. Assume that the length of the two mirrors is D, the offset angle is α (0<α<5mrad), the spacing is s, the cone angle of the pulsed laser incident on the mirror is θ, the distance from the intersection of the extension lines of the two mirrors to the end point of the mirror is r, and the speed of light is c; after the pulsed laser is incident through the diffraction grating, the first lens, the beam splitter, and the second lens, light of different wavelengths will be incident on the spectral time delay device at different angles, of which M beams of pulsed laser will return to the incident point along the incident light path, and the amount of returned light is:

[0029]

[0030] The numerical aperture of the spectral time delay is defined as:

[0031]

[0032] In the spectral time delay device, the maximum supported return light quantity is defined as:

[0033]

[0034] The optical path difference between two adjacent beams of returning light is:

[0035]

[0036] Compared with the existing technology, the beneficial effects of the present invention are as follows:

[0037] 1. Spectral time delay is a large-scale reconfigurable dispersion system, which is simple to build, stable and widely used. In the visible light band (taking 700nm as an example), if you want to introduce 1ns nm -1 The GVD of the optical fiber will have a loss of 50dB. However, when the same GVD is introduced by a spectral time delay device, the loss is only 4-7dB, which improves the system resolution and imaging clarity, and can achieve high-definition and accurate imaging effects.

[0038] 2. This system can use a pulsed laser with a repetition rate of more than 10MHz as the light source. Compared with the traditional kHz repetition rate, the scanning rate of this system is increased by 2 to 3 orders of magnitude, which greatly improves the imaging rate and can achieve high-speed imaging effects;

[0039] 3. This system combines an acousto-optic modulator with an arbitrary waveform generator. RF signals are used to modulate a piezoelectric converter to excite acoustic waves, which in turn influence the internal crystal, changing the refractive index of the crystal and, in turn, the angle of the outgoing light. This upgrades one-dimensional scanning to two-dimensional scanning, increasing the imaging dimension and enabling the acquisition of more image information. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A schematic structural diagram of a two-dimensional laser scanning system based on spectral angle enhancement and time delay provided in an embodiment of the present invention;

[0041] Figure 2 for Figure 1 Schematic diagram of the structure of the spectral time delay device;

[0042] Figure 3 Schematic diagram of how one-dimensional scanning light is converted into two-dimensional scanning light after passing through an acousto-optic modulator in an embodiment of the present invention. DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0044] See also Figure 1The two-dimensional scanning laser imaging system based on spectral angle enhancement and time delay provided by the present invention includes an incident laser module 1, a diffraction grating 2, a first lens 3, a spectroscope 4, a second lens 5, a spectral time delay 6, a tube lens 7, an objective lens 8, an arbitrary waveform generator 9, an acousto-optic modulator 10, a sample to be measured 11 and a data acquisition and processing component 12.

[0045] The incident laser module 1 generates a pulsed laser, which passes through the diffraction grating 2, the first lens 3, the beam splitter 4, the second lens 5, the spectral time delay 6, the second lens 5, the beam splitter 4, the tube lens 7, the objective lens 8, the acousto-optic modulator 10, the sample to be tested 11, and the data acquisition and processing component 12 in sequence.

[0046] The incident laser module 1 is used to generate high repetition rate pulsed laser;

[0047] The diffraction grating 2 is used to split the incident pulse laser spectrum, and the split pulse laser is emitted at a solid cone angle θ;

[0048] The first lens 3 is used to collimate the pulsed laser and control the divergence angle;

[0049] The beam splitter 4, the pulse laser after the spectral time delay 6 introduces group velocity dispersion to form M beams of return light, the M beams of return light are reflected by the beam splitter 4 and coupled to the tube lens 7 and the objective lens 8;

[0050] The second lens 5 is used to focus the pulsed laser into the spectral time delay 6;

[0051] The optical system is used to correct the aberration of the system and collimate;

[0052] The arbitrary waveform generator 9 is connected to the acousto-optic modulator 10. The arbitrary waveform generator 9 applies a periodic radio frequency signal to the acousto-optic modulator 10, which can periodically change the angle of the emitted light to generate a plurality of sub-beams of light, thereby converting the M beams of one-dimensional scanning light into two-dimensional scanning light, which is then incident on the sample to be tested.

[0053] After the two-dimensional scanning light scans the sample to be measured 11 , it is incident on the data acquisition and processing component 12 to obtain image information of the sample to be measured 11 .

[0054] In some embodiments of the present invention, the wavelength window of the incident laser module 1 is 400-800 nm.

[0055] In some embodiments of the present invention, see Figure 2The spectral time delay device 6 includes two mirrors with a certain offset angle α (0<α<5mrad) and high reflectivity (>99.5%), which are used to create a spatial chirped path and introduce group velocity dispersion to the pulsed laser in free space. The longer the wavelength of light, the greater the optical path difference τ introduced, thereby achieving the effect of introducing group velocity dispersion.

[0056] Assume that the two mirrors are of length D, offset at an angle α, and spaced s apart. The cone angle of the pulsed laser incident on the mirrors is θ. The distance from the intersection of the extended lines of the two mirrors to the end points of the mirrors is r. The speed of light is c. After the pulsed laser passes through the diffraction grating, the first lens, the beam splitter, and the second lens, light of different wavelengths will enter the spectral time delay device at different angles. M beams of pulsed laser light will return to the incident point along the incident light path. The amount of returned light is:

[0057]

[0058] The optical path difference between two adjacent beams of returning light is:

[0059]

[0060] In the spectral time delay device 6 , the optical path difference τ introduced to light with a longer wavelength is larger, thereby achieving the effect of introducing group velocity dispersion.

[0061] In some embodiments of the present invention, the tube lens 7 and the objective lens 8 form an infinity-corrected optical system. The return light is corrected for aberration by the tube lens 7 and then collimated by the objective lens 8 to form a one-dimensional scanning light. The one-dimensional scanning light is incident on the acousto-optic modulator 10.

[0062] In some embodiments of the present invention, see Figure 3 The AWG 9 is connected to the AOM 10. It generates a radio frequency signal and transmits it to the AOM 10. The piezoelectric transducer within the AOM 10 excites acoustic waves, influencing the crystal inside and changing the crystal's refractive index. Applying a periodic radio frequency signal to the AOM 10 using the AWG 9 periodically changes the angle of the emitted light, generating multiple sub-beams. This transforms the M beams of one-dimensional scanning light into two-dimensional scanning light, which is then incident on the sample to be tested.

[0063] In some embodiments of the present invention, the data acquisition and processing component 12 includes a high-speed photodetector, a real-time oscilloscope connected to the high-speed photodetector, and a computer. The components are used to convert the output optical signal into an electrical signal. The real-time oscilloscope is used to reconstruct the acquired signal to obtain the original image of the sample 11 to be tested, and the computer is used to process and analyze the data, thereby obtaining high-speed, clear, and accurate imaging. The bandwidth of the high-speed photodetector is >9 GHz, the bandwidth of the real-time oscilloscope is 4 to 20 GHz, and the scanning rate is 20 to 80 GSa s. -1 .

[0064] The present invention also provides a method for performing two-dimensional scanning laser imaging using the above system.

[0065] In some embodiments of the present invention, a two-dimensional scanning laser imaging method based on spectral angle enhancement and time delay includes the following steps:

[0066] A. The incident laser module 1 generates a pulsed laser that passes through the diffraction grating 2, which splits the pulsed laser into a spectrum with a three-dimensional cone angle θ. The split pulsed laser passes through the first lens 3 to collimate and prevent beam expansion. The pulsed laser then passes through the beam splitter 4, is focused by the second lens 5, and is incident on the spectral time delay 6.

[0067] B. Pulsed lasers of different wavelengths are incident on the spectral time delay device 6 at different angles. Light with longer wavelengths has a larger incident angle on the spectral time delay device, and the optical path difference introduced is also larger, thereby introducing group velocity dispersion in free space.

[0068] C. After introducing group velocity dispersion, M beams of pulsed laser light return along the incident optical path to the beam splitter 4. They are then reflected by the beam splitter 4 into the optical system consisting of the tube lens 7 and the objective lens 8. The return light is corrected for aberrations by the tube lens 7 and then collimated by the objective lens 8 to form M beams of one-dimensional scanning light. The one-dimensional scanning light is then incident on the acousto-optic modulator 10.

[0069] D. Arbitrary waveform generator 9 generates a radio frequency signal and sends it to the AOM 10. The piezoelectric transducer inside the AOM 10 excites acoustic waves and affects the crystal inside, changing the crystal's refractive index and, therefore, the angle of the emitted light. Using the arbitrary waveform generator 9 to apply a periodic radio frequency signal to the AOM 10 can periodically change the angle of the emitted light, generating multiple sub-beams, transforming the M beams of one-dimensional scanning light into two-dimensional scanning light, which is then incident on the sample to be tested.

[0070] E. After the two-dimensional scanning light scans the test sample 11, it passes through the data acquisition and processing component 12, and the data is processed and analyzed by the data acquisition and processing component 12, so as to obtain high-speed, clear and accurate imaging.

[0071] The present invention provides a high-speed two-dimensional scanning optical imaging system with a MHz-level scanning rate. It uses a spectral time delay device composed of two reflectors to form a large-scale reconfigurable dispersion system. The system is simple to build, has strong stability, and is widely applicable. In the visible light band (taking 700nm as an example), a 1ns nm -1 For GVD, using optical fiber will introduce a loss of more than 50dB, which is unacceptable. However, using a spectral time delay device will only introduce a loss of 4 to 7dB, which improves the system resolution while improving the imaging clarity, and can achieve high-definition and accurate imaging effects. At the same time, this system can use a pulsed laser with a repetition frequency of more than 10MHz as a light source. Compared with the traditional kHz repetition frequency, the scanning rate of this system is increased by 2 to 3 orders of magnitude, which greatly improves the imaging rate and can achieve high-speed imaging effects. Furthermore, this system combines an acousto-optic modulator with an arbitrary waveform generator, uses radio frequency signals to modulate the piezoelectric converter to excite acoustic waves, and exerts an influence on the internal crystal to change the refractive index of the crystal, thereby changing the angle of the emitted light, and upgrading the one-dimensional scan to a two-dimensional scan, thereby improving the imaging dimension and obtaining more image information.

[0072] The present invention can realize deep, high-speed and precise optical imaging in the visible light band, and has a wide range of uses in the fields of basic biology and biomedical diagnosis, and can promote the development of the field of biomedical imaging.

[0073] The above embodiment is one of the implementation methods of the present invention, but the implementation methods of the present invention are not limited to the embodiments and test examples. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A two-dimensional scanning laser imaging system based on spectral angle enhancement and time delay, characterized by: The device comprises an incident laser module (1), a diffraction grating (2), a first lens (3), a spectroscope (4), a second lens (5), a spectral time delay (6), an optical system, an arbitrary waveform generator (9), an acousto-optic modulator (10), a sample to be measured (11), and a data acquisition and processing component (12); The incident laser module (1) is used to generate pulsed laser; The diffraction grating (2) is used to split the incident pulse laser spectrum, and the incident pulse laser is emitted at a solid cone angle θ; The first lens (3) is used to collimate the pulsed laser and prevent beam expansion; The incident pulse laser passes through the beam splitter (4) and is incident on the spectrum time delay device (6) to form return light, and the return light is then reflected by the beam splitter (4) and coupled into the optical system composed of the lens barrel (7) and the objective lens (8); The second lens (5) is used to focus the pulsed laser and inject it into the spectral time delay device (6); The optical system is used to correct the aberration of the system and collimate; The arbitrary waveform generator (9) is connected to the acousto-optic modulator (10). The arbitrary waveform generator (9) applies a periodic radio frequency signal to the acousto-optic modulator (10), which can periodically change the angle of the emitted light, generate a plurality of sub-beams of light, and convert the M beams of one-dimensional scanning light into two-dimensional scanning light, which is then incident on the sample to be tested; After scanning the sample to be measured (11), the two-dimensional scanning light is incident on the data acquisition and processing component (12) to obtain image information of the sample to be measured (11); the spectral time delay device (6) includes two non-parallel mirrors with an offset angle α and a reflectivity greater than 99.5%, which are used to create a spatial chirp path and introduce group velocity dispersion to the pulsed laser in free space.

2. The two-dimensional scanning laser imaging system based on spectral angle enhancement and time delay according to claim 1, characterized in that: The wavelength window of the incident laser module (1) is 400-800 nm.

3. The two-dimensional scanning laser imaging system based on spectral angle enhancement and time delay according to claim 1, characterized in that: The incident laser module (1) is a high repetition frequency pulse laser.

4. The two-dimensional scanning laser imaging system based on spectral angle enhancement and time delay according to claim 1, characterized in that: The optical system comprises a tube lens (7) and an objective lens (8), wherein the tube lens (7) is used for correcting aberrations; and the objective lens (8) is used for collimating the return light and forming one-dimensional scanning light.

5. The two-dimensional scanning laser imaging system based on spectral angle enhancement and time delay according to claim 1, characterized in that: The offset angle α satisfies: 0<α<5mrad.

6. The two-dimensional scanning laser imaging system based on spectral angle enhancement and time delay according to any one of claims 1 to 5, characterized in that: The data acquisition and processing component (12) includes a high-speed photodetector, a real-time oscilloscope connected to the high-speed photodetector, and a computer. The high-speed photodetector is used to convert the output optical signal into an electrical signal. The real-time oscilloscope is used to reconstruct the collected signal to obtain the original image of the sample to be tested (11). The computer is used to process and analyze the data to obtain high-speed, clear, and accurate imaging.

7. A two-dimensional scanning laser imaging method based on spectral angle enhancement and time delay, characterized in that: The method is implemented using the system according to any one of claims 1 to 6, and the method comprises the following steps: The pulsed laser light generated by the incident laser module (1) passes through the diffraction grating (2), the diffraction grating (2) splits the pulsed laser light into a spectrum with a three-dimensional cone angle θ, and the split pulsed laser light is collimated by the first lens (3); The collimated pulse laser passes through the beam splitter (4), is focused by the second lens (5), and is incident on the spectrum time delay device (6) to introduce group velocity dispersion; After the introduction of group velocity dispersion, M beams of pulsed laser light will return to the incident point along the incident light path, and will be reflected into the optical system through the beam splitter (4). The returning light will form a one-dimensional scanning light through the optical system. The arbitrary waveform generator (9) generates a radio frequency signal and sends it to the acousto-optic modulator (10). The piezoelectric converter inside the acousto-optic modulator (10) will excite the sound wave and exert an influence on the crystal inside, thereby changing the refractive index of the crystal. The arbitrary waveform generator (9) is used to apply a periodic radio frequency signal to the acousto-optic modulator (10), which can periodically change the angle of the emitted light, generate a plurality of sub-beams, and transform the M beams of one-dimensional scanning light into two-dimensional scanning light, which is then incident on the sample to be measured; After the two-dimensional scanning light scans the sample to be tested (11), image information of the sample to be tested is obtained through the data acquisition and processing component (12).

8. The two-dimensional scanning laser imaging method based on spectral angle enhancement and time delay according to claim 7, characterized in that: The optical system comprises a barrel lens (7) and an objective lens (8); the return light first passes through the barrel lens (7) in the optical system to correct aberrations, and then passes through the objective lens (8) for collimation to ultimately form one-dimensional scanning light.

9. The two-dimensional scanning laser imaging method based on spectral angle enhancement and time delay according to any one of claims 7-8, characterized in that: The spectral time delay device (6) includes two non-parallel mirrors with a reflectivity greater than 99.5%, which are used to create a spatial chirped path and introduce group velocity dispersion to the pulsed laser in free space. Assume that the length of the two mirrors is D, the offset angle is α and 0<α<5mrad, the spacing is s, the cone angle of the pulsed laser incident on the mirror is θ, the distance from the intersection of the extension lines of the two mirrors to the end point of the mirror is r, and the speed of light is c. After the pulsed laser is incident on the diffraction grating (2), the first lens (3), the beam splitter (4), and the second lens (5), light of different wavelengths will be incident on the spectral time delay device (6) at different angles, among which M beams of pulsed laser will return to the incident point along the incident light path, and the amount of returned light is: The numerical aperture of the spectral time delay is defined as: In the spectral time delay (6), the maximum supported return light quantity is defined as: The optical path difference between two adjacent beams of returning light is:

Images