Ultrafast scanning measurement system of absorption loss distribution in spatial and frequency domains of optical elements based on dispersive Fourier transform

Abstract

The present application provides an ultrafast scanning measurement system for the spatial and frequency domain distribution of absorption loss of optical elements based on dispersion Fourier transform, including: an ultrashort pulse laser, a spatial light focusing and collection module, a laser average spectrum measurement module, a single pulse real-time spectrum measurement module based on dispersion Fourier transform, a time lens module, a high-speed photodetector and a high-frequency oscilloscope. Based on the principle of dispersion Fourier transform, the present application can demodulate the real-time spectrum of a single pulse, and can use the scanning detection module to use the light pulse repetition period as the scanning frame rate of the optical element to achieve ultrafast scanning detection of the spatial two-dimensional distribution of the absorption rate of the optical element, providing a means for high-efficiency and comprehensive detection of thermal absorption of large-caliber optical elements.

Description

Technical Field

[0001] The present application belongs to the technical field of optical element detection, and more specifically, to an ultrafast scanning measurement system for the spatial and frequency domain distribution of optical element absorption loss based on dispersion Fourier transform. Background Art

[0002] In high-energy laser systems, optical components are exposed to strong radiation power, and the heat absorption of mirrors, films, and substrate materials is a key factor in causing component surface distortion and stress damage. Such thermal distortion and thermal damage will cause aberrations to the internal optical transmission channel of the laser system, and even cause associated damage to downstream optical components. Therefore, the spatial two-dimensional distribution of optical component absorption loss determines the strong light resistance of the optical transmission channel in the laser system and limits the output power of the laser system. In addition, with the in-depth application of high-energy laser technology in national defense, military, processing and manufacturing, fusion energy and other fields, laser systems have gradually integrated multiple functions such as lighting, detection, calibration, and beacons. Therefore, there will be multiple bands of lasers in the system at the same time, making the film design of optical components extremely complex. Therefore, the absorption rate of optical components to lasers of different bands (absorption rate frequency domain distribution) is a key parameter for comprehensively evaluating the thermal absorption of strong light components.

[0003] At present, the absorption loss of optical components is measured by laser calorimetry technology, which requires a laser light source with the wavelength used by the optical component to be focused on the surface of the optical component to be measured through a lens; the detection light source measures the change in the intensity of the center of the reflected or transmitted detection beam after a certain distance, thereby obtaining the absorption rate of the measured point. Since laser calorimetry technology requires long-term measurement, for large-aperture optical components, it will take several days or even months to measure the absorption loss of each spatial point of the full aperture at a spatial resolution of the micron level. And because the pump light is a single-wavelength laser light source with the wavelength used by the optical component, it is impossible to obtain the frequency domain distribution of the absorption loss through a single measurement. If the pump light source is replaced for re-measurement, the detection time efficiency of the optical component will be reduced exponentially.

[0004] The original intention of this application is to achieve ultrafast scanning measurement of the spatial and frequency distributions of absorption loss, and to provide a means for comprehensive and efficient detection of thermal absorption of large-aperture optical components. Summary of the invention

[0005] To achieve the above purpose, the technical solution adopted in this application is to provide an ultrafast scanning measurement system for the spatial and frequency domain distribution of absorption loss of optical elements based on dispersion Fourier transform, including:

[0006] An ultrashort pulse laser for emitting probe light in the form of a train of optical pulses;

[0007] A spatial light focusing and collecting module is used to converge the detection light in the spatial domain, irradiate the detected optical element, and collect the detection light reflected / transmitted by the detected optical element;

[0008] A laser average spectrum measurement module, connected to the spatial light focusing and collection module, for measuring the average spectrum of ultrashort pulse output laser under multi-pulse cycles;

[0009] A single pulse real-time spectrum measurement module based on dispersion Fourier transform is used to perform dispersion Fourier transform on the probe light reflected / transmitted by the optical element under test;

[0010] The time lens module is used to stretch and amplify the real-time spectrum of the detection light after the dispersion Fourier transform in the time domain to obtain the real-time spectrum of each single pulse;

[0011] High-speed photodetectors and high-frequency oscilloscopes are used to perform photoelectric conversion and acquisition on the time-domain stretched optical pulses.

[0012] Optionally, it also includes a circulator and a coupler, the input end of the coupler is connected to the output end of the ultrashort pulse laser, the first output end of the coupler is connected to the first end of the circulator, the second end of the circulator is connected to the spatial light focusing and collection module, and the third end of the circulator is connected to the single pulse real-time spectrum measurement module based on dispersion Fourier transform.

[0013] Optionally, the laser average spectrum measurement module is a spectrometer, and the spectrometer is connected to the second output end of the coupler.

[0014] Optionally, the spatial light focusing and collecting module includes a two-dimensional mobile platform, the two-dimensional mobile platform includes a collimator and a focusing lens, the collimator is connected to the second end of the circulator, and the detection light is converged on the optical element to be measured through the collimator and the focusing lens.

[0015] Optionally, the spatial light focusing and collecting module includes a scanning galvanometer, the scanning galvanometer is connected to the second end of the circulator, and the detection light is focused on the optical element to be measured through the scanning galvanometer.

[0016] The beneficial effects of the ultrafast scanning measurement system for the spatial and frequency domain distribution of optical element absorption loss based on dispersion Fourier transform provided by the present application are:

[0017] The present application utilizes an ultrashort pulse laser as a detection light source, and performs point scanning measurement on the absorption rate of the optical element under test with a high repetition frequency pulse train, achieving a point scanning refresh frame rate above the MHz level, greatly reducing the absorption loss detection time of large-aperture optical elements.

[0018] The present application utilizes a single-pulse real-time spectral measurement technology based on the principle of dispersion Fourier transform, takes the pulse repetition period as the spectral measurement refresh frame rate, and realizes ultrafast demodulation of the frequency domain distribution of the single-point absorption rate of the measured optical element.

[0019] The present application utilizes a time lens module to achieve time-domain stretching and amplification of the spectrum, thereby improving the time and frequency domain resolution of the detection system.

[0020] The present application utilizes a two-dimensional displacement platform or a scanning galvanometer to measure the spatial distribution of the absorption rate of an optical element.

[0021] This application can be widely used in the fields of optical component detection, laser system health management online monitoring, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0023] Figure 1 A schematic diagram of the structure of an ultrafast scanning measurement system for the spatial and frequency domain distribution of absorption loss of an optical element based on dispersion Fourier transform provided in an embodiment of the present application;

[0024] Figure 2 A schematic diagram of the measurement results of the spatial and frequency domain distribution of the absorption rate of the optical element under test provided in an embodiment of the present application;

[0025] Figure 3 This is the time lens module composition diagram and the time lens function diagram. DETAILED DESCRIPTION

[0026] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0027] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0028] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0029] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0030] Please also read Figure 1-Figure 3 , the ultrafast scanning measurement system of the spatial and frequency domain distribution of absorption loss of an optical element based on dispersion Fourier transform provided in an embodiment of the present application is now described.

[0031] An ultrafast scanning measurement system for the spatial and frequency domain distribution of absorption loss of an optical element based on dispersion Fourier transform, comprising:

[0032] An ultrashort pulse laser for emitting probe light in the form of a train of optical pulses;

[0033] A spatial light focusing and collecting module is used to converge the detection light in the spatial domain, irradiate the detected optical element, and collect the detection light reflected / transmitted by the detected optical element;

[0034] A laser average spectrum measurement module, connected to the spatial light focusing and collection module, for measuring the average spectrum of ultrashort pulse output laser under multi-pulse cycles;

[0035] A single pulse real-time spectrum measurement module based on dispersion Fourier transform is used to perform dispersion Fourier transform on the probe light reflected / transmitted by the optical element under test;

[0036] The time lens module is used to stretch and amplify the real-time spectrum of the detection light after the dispersion Fourier transform in the time domain to obtain the real-time spectrum of each single pulse;

[0037] High-speed photodetectors and high-frequency oscilloscopes are used to perform photoelectric conversion and acquisition on the time-domain stretched optical pulses.

[0038] The present application connects one path of the ultrashort pulse laser to the laser average spectrum measurement module to measure the average spectrum of the detection light; the other path is converged on the optical element to be measured through the spatial light focusing and collection module; the reflected or transmitted detection light is subjected to dispersion Fourier transform through the single pulse real-time spectrum measurement module based on dispersion Fourier transform, the pulse light is dispersion stretched, the spectral shape of the detection light and the linear mapping of the pulse envelope are realized, and the light pulses after dispersion stretching are photoelectrically converted and collected by a high-speed photodetector and a high-frequency oscilloscope, and finally the real-time spectrum of each single pulse is obtained; the frequency domain distribution of the absorption rate of a single point of the optical element to be measured is obtained by comparing the average spectrum of the detection light measured by the laser average spectrum measurement module with the real-time spectrum of a single pulse measured by the high-frequency oscilloscope; since the ultrashort pulse laser has a light pulse repetition frequency of more than MHz, and the real-time spectrum of a single pulse can be demodulated based on the principle of dispersion Fourier transform, the scanning detection module can be used to use the light pulse repetition period as the scanning frame rate of the optical element to realize ultrafast scanning detection of the spatial two-dimensional distribution of the absorption rate of the optical element.

[0039] In some embodiments of the present application, see Figure 1 The ultrafast scanning measurement system of the spatial and frequency domain distribution of absorption loss of optical elements based on dispersion Fourier transform also includes a circulator and a coupler, the input end of the coupler is connected to the output end of the ultrashort pulse laser, the first output end of the coupler is connected to the first end of the circulator, the second end of the circulator is connected to the scanning detection module, and the third end of the circulator is connected to the single pulse real-time spectrum measurement module based on dispersion Fourier transform.

[0040] The single pulse real-time spectrum measurement module based on dispersion Fourier transform injects the detection light reflected / transmitted by the measured optical element into the transmission medium with group velocity dispersion. The pulse light will produce a walk-off effect due to the different group delays experienced by different frequency components, so that the pulse envelope evolves into its spectral shape. The high-wavelength resolution real-time demodulation of the single pulse spectrum is completed through a high-speed photodetector and a high-frequency oscilloscope to obtain the frequency domain distribution of the absorption rate of a single point of the measured optical element.

[0041] In some embodiments of the present application, see Figure 1 The laser average spectrum measurement module is a spectrometer, and the spectrometer is connected to the second output end of the coupler.

[0042] In some embodiments of the present application, see Figure 1 The spatial light focusing and collecting module includes a two-dimensional mobile platform, the two-dimensional mobile platform includes a collimator and a focusing lens, the second end of the circulator is connected to the first end of the collimator, the second end of the collimator is aligned with the input end of the focusing lens, and the output end of the focusing lens is aligned with the optical element to be measured.

[0043] In other embodiments of the present application, see Figure 1 The spatial light focusing and collecting module includes a scanning galvanometer, the second end of the circulator is connected to the input end of the scanning galvanometer, and the output end of the scanning galvanometer is aligned with the optical element to be measured.

[0044] The above two implementations are applicable to detecting reflective optical elements, and are also applicable to detecting transmissive optical elements. The specific implementation is to add a standard reflector or the same emitting device to collect the detection light behind the sample to be tested, and other devices remain unchanged. In this way, the transmitted detection light can also be collected.

[0045] Working principle:

[0046] One path of an ultrashort pulse laser such as a highly coherent and wide-band ultrafast laser or a supercontinuum laser is connected to a spectrometer to measure the average spectrum of the detection laser; the other path is converged on the optical element to be measured through a collimator and a focusing lens (or converged on the optical element to be measured through a scanning galvanometer). The reflected or transmitted detection light is subjected to dispersion Fourier transform through the dispersion module, and the pulse light is dispersion stretched to realize linear mapping between the spectral shape of the detection light and the pulse envelope. The light pulses after dispersion stretching are photoelectrically converted and collected by a high-speed photodetector and a high-frequency oscilloscope. The real-time spectrum of the detection light is time-stretched and amplified by the time lens module, and finally the real-time spectrum of each single pulse is obtained. The frequency domain distribution of the absorption rate of a single point of the optical element under test is obtained by comparing the average spectrum of the detection light measured by the spectrometer with the real-time spectrum of a single pulse measured by the oscilloscope. Since the ultrashort pulse laser has a light pulse repetition frequency of more than MHz and the real-time spectrum of a single pulse can be demodulated based on the principle of dispersion Fourier transform, a two-dimensional mobile platform or a scanning galvanometer can be used to use the light pulse repetition period as the optical element point scanning frame rate to realize ultrafast scanning detection of the spatial two-dimensional distribution of the absorption rate of the optical element.

[0047] Figure 1 The scanning method provided in the embodiment of the present application is a scanning galvanometer or a two-dimensional displacement platform, and the two-dimensional distribution of the absorption rate of the optical element under test is measured at a spatial resolution of the micrometer level. Each detection light pulse (1, 2, 3, ...) corresponds to each single point area (1, 2, 3, ...) under test, and the real-time spectrum corresponding to the single pulse is measured by dispersive Fourier transform. By comparing with the average spectrum of the detection laser measured by the spectrometer, the frequency domain distribution of the absorption rate of each scanning point of the optical element under test is measured.

[0048] See also Figure 2 , Figure 2 The figure is a schematic diagram of the measurement results of the spatial and frequency domain distribution of the absorption rate of the optical element under test. Figure 1The specific embodiment uses a scanning galvanometer or a two-dimensional displacement platform to measure the two-dimensional distribution of the absorption rate of the optical element under test at a spatial resolution of micrometers. Each detection light pulse (1, 2, 3, ...) corresponds to each single point area (1, 2, 3, ...) under test, and the real-time spectrum corresponding to the single pulse is measured by dispersion Fourier transform. By comparing with the average spectrum of the detection laser measured by the spectrometer, the frequency domain distribution of the absorption rate of each scanning point of the optical element under test is measured.

[0049] See also Figure 3 , which is the composition diagram of the time lens module and the function diagram of the time lens. After dispersion compensation and four-wave mixing, the spectrum is stretched and amplified in the time domain through filtering.

[0050] The ultrafast scanning measurement system for the spatial and frequency domain distribution of absorption loss of optical elements based on dispersive Fourier transform provided in the present application can realize ultrafast scanning measurement of the spatial and frequency domain distribution of absorption loss, providing a means for efficient and comprehensive detection of thermal absorption of large-aperture optical elements.

[0051] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. An ultrafast scanning measurement system for the spatial and frequency domain distribution of optical element absorption loss based on dispersion Fourier transform, characterized in that: include: An ultrashort pulse laser for emitting probe light in the form of a train of optical pulses; A spatial light focusing and collecting module is used to converge the detection light in the spatial domain, irradiate the detected optical element, and collect the detection light reflected / transmitted by the detected optical element; A laser average spectrum measurement module, connected to the spatial light focusing and collection module, for measuring the average spectrum of ultrashort pulse output laser under multi-pulse cycles; A single pulse real-time spectrum measurement module based on dispersion Fourier transform is used to perform dispersion Fourier transform on the probe light reflected / transmitted by the optical element under test; The time lens module is used to stretch and amplify the real-time spectrum of the detection light after the dispersion Fourier transform in the time domain to obtain the real-time spectrum of each single pulse; High-speed photodetectors and high-frequency oscilloscopes are used to perform photoelectric conversion and acquisition on the time-domain stretched optical pulses.

2. The ultrafast scanning measurement system for the spatial and frequency domain distribution of optical element absorption loss based on dispersion Fourier transform as claimed in claim 1, characterized in that: It also includes a circulator and a coupler, wherein the input end of the coupler is connected to the output end of the ultrashort pulse laser, the first output end of the coupler is connected to the first end of the circulator, the second end of the circulator is connected to the spatial light focusing and collection module, and the third end of the circulator is connected to the single-pulse real-time spectrum measurement module based on dispersion Fourier transform.

3. The ultrafast scanning measurement system for the spatial and frequency domain distribution of optical element absorption loss based on dispersion Fourier transform as claimed in claim 2, characterized in that: The laser average spectrum measurement module is a spectrometer, and the spectrometer is connected to the second output end of the coupler.

4. The ultrafast scanning measurement system for the spatial and frequency domain distribution of optical element absorption loss based on dispersion Fourier transform as claimed in claim 2, characterized in that: The spatial light focusing and collecting module comprises a two-dimensional mobile platform, which comprises a collimator and a focusing lens. The collimator is connected to the second end of the circulator, and the detection light is converged on the optical element to be measured through the collimator and the focusing lens.

5. The ultrafast scanning measurement system for the spatial and frequency domain distribution of optical element absorption loss based on dispersion Fourier transform as claimed in claim 2, characterized in that: The spatial light focusing and collecting module comprises a scanning galvanometer, which is connected to the second end of the circulator, and the detection light is focused on the optical element to be measured through the scanning galvanometer.

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