Three-dimensional imaging device and method based on FP cavity laser and its associated radiation transmission

Abstract

The present invention proposes a three-dimensional imaging method and an implementation device for laser and its associated radiation transmission based on an F-P cavity, and relates to the field of imaging of laser and its associated radiation transmission. The present invention inserts an F-P cavity in a forward imaging system to reflect and transmit the laser and its associated radiation multiple times, so as to increase the image distance multiple times and change the position of the object section corresponding to the imaging spot, thereby simultaneously imaging different sections of the laser and its associated radiation transmission. The characteristics of the present invention are that it can control the distance between the object sections corresponding to different imaging spots in a single time by adjusting the distance between the two reflecting surfaces of the F-P cavity; by adjusting the incident angle of the F-P cavity, the object measurement range can be fine-tuned, and the spatial separation degree of the imaging spots can be adjusted; by measuring the transmission and reflection coefficient of the F-P cavity, the intensity of the imaging spots at each level is corrected to obtain a three-dimensional imaging diagram of the laser and its associated radiation transmission. This method can realize three-dimensional spatial measurement of laser linear and nonlinear transmission and its induced associated radiation.

Description

Technical Field

[0001] The present invention relates to the field of laser transmission in transparent media and its application, and in particular to the field of laser and its associated radiation transmission imaging. Background Art

[0002] The process of laser transmission in a transparent medium undergoes a transition from linear to nonlinear, and even to extremely nonlinear, as the light intensity increases from low to high. These processes are often accompanied by a wealth of physical phenomena, leading to numerous applications. For example, the transmission and evolution of lasers include changes in the spatial distribution of light intensity, namely focusing and defocusing; the dispersion phenomenon caused by the different refractive indices of various colors of light along the propagation direction when ultrashort pulse lasers pass through a medium; and the filamentation phenomenon, a dynamic equilibrium between Kerr self-focusing and plasma self-defocusing of high-intensity femtosecond lasers in a transparent medium. Laser transmission also stimulates corresponding associated radiation phenomena, such as frequency conversion during laser transmission in nonlinear media; terahertz radiation and third harmonic radiation stimulated by femtosecond laser filamentation; and supercontinuum generation.

[0003] In traditional imaging systems for lasers and their associated radiation, a camera is usually used to image a single cross-section of the object beam. If it is necessary to observe the evolution of the laser and its associated radiation within a certain measurement range, the position of the camera and imaging lens needs to be changed multiple times. This not only makes the experimental process cumbersome, but also makes it impossible to guarantee the accuracy of the experimental results due to human error.

[0004] The FP cavity is a cavity composed of two lenses with a certain reflectivity. When a beam of light enters the FP cavity, part of the beam is reflected and part is transmitted. When the transmitted light hits another reflective surface, part of the light is reflected and part of the light is transmitted. The reflected light is reflected and transmitted on another reflective surface again. This reciprocating process can increase the optical path multiple times.

[0005] The present invention has discovered that when the FP cavity is used in the imaging of laser and its associated radiation, if the distance between the two reflecting surfaces of the FP cavity and the angle of the FP cavity are adjusted to the desired appropriate values, the FP cavity can be used as a new auxiliary imaging instrument, so that the system can image multiple sections within the measurement range at the same time and under the same conditions, thereby accurately and conveniently observing the three-dimensional image of the laser and its associated radiation. Summary of the Invention

[0006] The object of the present invention is to address the deficiencies of the above-mentioned prior art, and provide a three-dimensional imaging method and its implementation device for the transmission of laser and its associated radiation based on an F-P cavity. Using the F-P cavity as a new auxiliary imaging instrument, the system can perform multi-section imaging within the measurement range under the same time and the same conditions, so as to accurately and conveniently observe the three-dimensional image of the laser and its associated radiation.

[0007] The technical solution of the present invention is as follows:

[0008] A three-dimensional imaging device for the transmission of laser and its associated radiation based on an F-P cavity, characterized in that it includes an imaging lens and an imaging device arranged in sequence along the optical path. The imaging device is externally connected to a computer, and an F-P cavity is arranged coaxially between the imaging lens and the imaging device, so that the laser and its associated radiation are reflected and transmitted multiple times in the F-P cavity, thereby increasing the image distance and changing the position of the object section corresponding to the imaging spot, and realizing simultaneous imaging of different sections.

[0009] By adjusting the distance between the two end mirrors of the F-P cavity, the distance between the object sections corresponding to different imaging spots at a single time is controlled; by adjusting the incident angle of the incident light of the F-P cavity, the object-side measurement range is finely adjusted, and the spatial separation degree of the imaging spots is controlled, so that the imaging spots can be separated in space.

[0010] The two end mirrors of the F-P cavity are parallel to each other, and the distance between the image planes corresponding to two adjacent-order imaging spots is approximately the same.

[0011] Let the focal length of the imaging lens be f, and the distance from the imaging lens to the imaging device be d. Then when d = 2f, an inverted and equal-sized real image is formed; when d > 2f, an inverted and enlarged real image is formed; when f < d < 2f, an inverted and reduced real image is formed.

[0012] The imaging device can select cameras such as CCD, ICCD, EMCCD, sCMOS, etc. with appropriate response bands and appropriate dynamic ranges according to the characteristics of the laser and its associated radiation to be measured, and can adjust the spacing and incident angle of the F-P cavity by referring to the dynamic range of the camera to select an appropriate imaging range and spatial resolution accuracy.

[0013] Preferably, it also includes a converging lens, a high-reflectivity mirror and a filter arranged in sequence along the output light direction of the laser; the laser output by the laser is focused by the converging lens to form a filament, and after a part of the light is reflected by the high-reflectivity mirror, the light intensity is weakened by the filter, and then focused by the imaging lens. After multiple reflections and transmissions of the FP cavity in a specific working band, the image is formed on the imaging device. The angle of the FP cavity and the distance between the two reflecting lenses are adjusted to maximize the number of images on the imaging device without overlapping each other. The imaging lens and the imaging device are moved simultaneously along the optical axis, and the intensity of the primary light spot is observed to find the starting point of laser filamentation and then the positions of the imaging lens and the imaging device are fixed.

[0014] A three-dimensional imaging method based on FP cavity laser and its associated radiation transmission includes the following steps:

[0015] ① The laser beam to be imaged and its accompanying radiation transmission area are formed by the converged laser beam, which passes through the imaging lens and FP cavity in sequence and is imaged on the imaging device;

[0016] ② Adjusting the distance between the reflectors at both ends of the FP cavity to image the laser focus area;

[0017] ③ Adjust the incident angle of the FP cavity to maximize the number of images on the imaging device without overlapping;

[0018] ④ According to the properties of the light beam to be measured, select an imaging device with a suitable dynamic range and working mode, set the appropriate trigger delay and exposure time, record and save the imaging image, and take and save the background image under the condition of no light beam;

[0019] ⑤Remove the background intensity from the image obtained in step ④;

[0020] ⑥ Make the laser directly image on the imaging device through the FP cavity, keep other conditions unchanged, record and save the imaging picture, and take and save the background picture under the condition of no beam;

[0021] ⑦Remove the background intensity from the image obtained in step ⑥;

[0022] ⑧ Extract the circular area where the n-level light spot is located in the image processed by step ⑦ and calculate the integral as the n-level light spot intensity I n , n=0,1,2……, then the square of the reflection coefficient R of the FP cavity (6) 2 =I n+1 / I n ;

[0023] ⑨ Extract the circular area where the n-level spot is located in the image processed by step ⑤ divided by R 2n , so that each level of light spot is corrected to the same level, thereby obtaining a three-dimensional image of the laser and its accompanying radiation transmission.

[0024] The degree of convergence of the light beam can be changed by adding a converging lens or concave mirror in the optical path. Alternatively, by selecting FP cavities in different wavelength ranges, three-dimensional imaging of the transmission evolution process of lasers in a specific wavelength band and their associated radiation can be achieved.

[0025] Compared with the prior art, the present invention has the following significant advantages:

[0026] 1) This method can simultaneously image multiple sections of the object laser and its associated radiation without changing the position of the imaging device and imaging lens, greatly reducing human error and simplifying the experimental steps;

[0027] 2) This method can selectively perform three-dimensional imaging of different wavelength ranges of laser and its associated radiation by selecting FP cavities and neutral density filters in different wavelength ranges, as well as cameras with appropriate dynamic ranges and operating modes;

[0028] 3) The three-dimensional images of laser light and its associated radiation obtained by this method can clearly and intuitively display the three-dimensional spatial transmission evolution process of laser light and its associated radiation, facilitating research and application by experimental personnel;

[0029] 4) The experimental device and optical path corresponding to this method are relatively simple, data processing is relatively easy, the experimental results are relatively accurate, and the implementation cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the structure of a three-dimensional imaging device embodiment of the present invention based on FP cavity laser and its associated radiation

[0031] Figure 2 This is a schematic diagram of the structure of the device corresponding to the three-dimensional imaging method of the present invention based on the third harmonic radiation transmission of the femtosecond filament associated with the FP cavity DETAILED DESCRIPTION

[0032] The present invention is described in detail below with reference to the embodiments and drawings, but the scope of protection of the present invention shall not be limited thereby:

[0033] Example 1:

[0034] See also Figure 1 , Figure 1This is a schematic diagram of an embodiment of a three-dimensional imaging device based on an FP cavity-based femtosecond filament and its associated radiation transmission. In this embodiment, the imaging device utilizes a CCD. The focal length of the imaging lens is f, and the distance from the imaging lens to the imaging device is d. As shown in the figure, a femtosecond laser 1 outputs laser light with a wavelength of 1030 nm, a frequency of 1 kHz, and a single pulse energy of 400 uJ. This light is focused by a converging lens 2 to form a filament. After being partially reflected by a 1030 nm high-reflectivity mirror 3, the light intensity is reduced by a neutral filter 4. The filament is then focused by an imaging lens 5 and, after multiple reflections and transmissions through an FP cavity 6 operating in the 1030 nm operating band, is imaged on a CCD 7. The CCD is triggered by a laser. The laser's focal area is imaged by adjusting the distance between the two reflective lenses of the FP cavity 6, which are parallel to each other. The angle of the FP cavity is also adjusted to maximize the number of images on the CCD without overlapping. Simultaneously move the imaging lens 5 and CCD 7 along the optical axis, maintaining a distance of 2f between them. Observe the intensity of the primary spot to find the point where the laser begins to form filaments, then fix the positions of the imaging lens 5 and CCD 7. The CCD 7 captures the image and background, transmits them to a computer, and processes the data to produce a 3D image.

[0035] A three-dimensional imaging method based on FP cavity laser and its associated radiation transmission specifically comprises the following steps:

[0036] ① The laser light output by the femtosecond laser 1 is focused by the converging lens 2 and formed into a filament. After being reflected by the 1030nm high reflectivity mirror 3 to remove a portion of the light, the light intensity is weakened by the neutral filter 4. It is then focused by the imaging lens 5 and imaged by the CCD 7 after multiple reflections and transmissions by the FP cavity 6 in the 1030nm working band. The computer records and saves the image and background image, and removes the background intensity from the image.

[0037] ② Remove the converging lens 2 so that the laser light is directly imaged on the CCD 7 through the FP cavity 6, keep other conditions unchanged, record and save the image and background images, and remove the background intensity from the image;

[0038] ③ Extract the circular area where the n-level light spot is located in the image processed by step ② and calculate the integral as the n-level light spot intensity I n , n=0,1,2……, then the square of the reflection coefficient of FP cavity 6 is R 2 =I n+1 / I n ;

[0039] ④ Extract the circular area where the n-level spot is located in the image processed by step ① divided by R 2n , so that each level of light spot is corrected to the same level, thereby obtaining a three-dimensional image of the femtosecond filament and its accompanying radiation transmission.

[0040] Example 2:

[0041] See also Figure 2 , Figure 2 This is a schematic diagram of the structure of the apparatus corresponding to the three-dimensional imaging method for the transmission of third harmonic radiation associated with femtosecond filaments using an FP cavity. When performing three-dimensional imaging of the third harmonic radiation associated with femtosecond filaments, a 1030nm high-reflectivity mirror 3 is used, a 343nm narrowband filter is used as filter 4, and an FP cavity 6 of the corresponding wavelength band is selected. The remaining operations are the same as in Example 1, and the evolution of the third harmonic radiation associated with the transmission of the femtosecond filaments can be observed.

[0042] Experiments show that the three-dimensional images of laser and its associated radiation obtained by the present invention using the three-dimensional imaging method of laser and its associated radiation transmission based on the FP cavity and the implementation device thereof simplify the experimental steps, reduce human errors, and can clearly and intuitively display the evolution process of laser and its associated radiation, providing convenience for the research and application of laser and its associated radiation.

Claims

1. A three-dimensional imaging device based on FP cavity laser and its associated radiation transmission, characterized in that , including an imaging lens and an imaging device arranged in sequence along the optical path. The imaging device is externally connected to a computer. An F-P cavity is arranged coaxially between the imaging lens and the imaging device, enabling the laser and its associated radiation to be reflected and transmitted multiple times within the F-P cavity, thereby increasing the image distance, changing the position of the object cross-section corresponding to the imaging spot, and achieving simultaneous imaging of different cross-sections; By adjusting the distance between the two reflectors at both ends of the F-P cavity, the distance between the object cross-sections corresponding to different single imaging spots is controlled; by adjusting the incident angle of the incident light of the F-P cavity, the object-side measurement range is finely adjusted, and the spatial separation degree of the imaging spots is controlled, making the imaging spots separable in space.

2. The three-dimensional imaging device based on FP cavity laser and its associated radiation transmission according to claim 1, characterized in that: The reflectors at both ends of the F-P cavity are parallel to each other, and the distance between the image planes corresponding to two adjacent-order imaging spots is approximately the same.

3. The three-dimensional imaging device based on FP cavity laser and its associated radiation transmission according to claim 1, characterized in that: Let the focal length of the imaging lens be f, and the distance from the imaging lens to the imaging device be d. Then when d = 2f, an inverted and equal-sized real image is formed; when d > 2f, an inverted and enlarged real image is formed; when f < d < 2f, an inverted and reduced real image is formed.

4. The three-dimensional imaging device based on FP cavity laser and its associated radiation transmission according to claim 1, characterized in that: The imaging device can select a CCD, ICCD, EMCCD, sCMOS camera with a suitable response band and a suitable dynamic range according to the characteristics of the laser and its associated radiation to be measured, and refer to the dynamic range of the camera to adjust the distance between the two ends of the F-P cavity and the incident angle, and select a suitable imaging range and spatial resolution accuracy.

5. The three-dimensional imaging device based on FP cavity laser and its associated radiation transmission according to claim 1, characterized in that: It also includes a converging lens (2), a high-reflectivity mirror, and a filter arranged in sequence along the output light direction of the laser (1); the laser output by the laser (1) is filamented after being focused by the converging lens (2), and after a part of the light is reflected by the high-reflectivity mirror, the light intensity is weakened by the filter, and then focused by the imaging lens (5). After multiple reflections and transmissions by the F-P cavity (6) of a specific working band, it is imaged on the imaging device. The angle of the F-P cavity (6) and the distance between the two reflector lenses are adjusted to maximize the number of images on the imaging device and make them non-overlapping. The imaging lens and the imaging device are simultaneously moved along the optical axis. After finding the filament starting point of the laser by observing the intensity of the first-order spot, the positions of the imaging lens (5) and the imaging device (7) are fixed.

6. A three-dimensional imaging method based on FP cavity laser and its associated radiation transmission, characterized in that: The method includes the following steps: ① The converged laser forms a transmission area of the laser and its associated radiation to be imaged, and after passing through the imaging lens and the F-P cavity in sequence, it is imaged on the imaging device; ② Adjust the distance between the two reflectors at both ends of the F-P cavity to image the laser focusing area; ③ Adjust the incident angle of the F-P cavity to maximize the number of images on the imaging device and make them non-overlapping; ④ According to the properties of the待测光束 (to-be-measured beam), select an imaging device with a suitable dynamic range and working mode, set a suitable trigger delay and exposure time, record and save the imaging pictures, and take and save the background pictures under the condition of no beam; ⑤ Remove the background intensity from the imaging pictures obtained in step ④; ⑥ Make the laser directly pass through the F-P cavity and be imaged on the imaging device, keep other conditions unchanged, record and save the imaging pictures, and take and save the background pictures under the condition of no beam; ⑦ Remove the background intensity from the imaging pictures obtained in step ⑥; ⑧ Extract the circular area where the n-level light spot is located in the image processed by step ⑦ and calculate the integral as the n-level light spot intensity I n , n=0,1,2……, then the square of the reflection coefficient R of the FP cavity (6) 2 =I n+1 / I n ; ⑨ Extract the circular area where the n-level spot is located in the image processed by step ⑤ divided by R 2n , so that each level of light spot is corrected to the same level, thereby obtaining a three-dimensional image of the laser and its accompanying radiation transmission.

7. The three-dimensional imaging method based on FP cavity laser and its associated radiation transmission according to claim 6, characterized in that: A converging lens or concave mirror is added to the optical path to change the convergence degree of the light beam. By selecting FP cavities in different wavelength ranges, three-dimensional imaging of the transmission evolution process of lasers in a specific wavelength band and their associated radiation can be achieved.

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