A dynamic performance calibration system and method for a streak camera slow scan stage

Abstract

The present application relates to a kind of dynamic performance calibration system for the slow scanning gear of streak camera, mainly for solving the technical problems that the method of existing extension light path is more complex, usually needs to extend more than 60 meters, experimental platform occupies too large area, it is difficult to realize, and it will lead to high light intensity attenuation.The light pulse output by the laser enters the output imaging of streak camera in the dynamic performance calibration system for the slow scanning gear of streak camera, and the electric pulse signal output by the laser enters the digital delay under the slow scanning gear, the digital delay adjusts the electric pulse signal, so that the trigger signal after adjustment is kept in synchronization with the light pulse, and the image output by streak camera is read by camera and analyzed.The present application also provides a kind of dynamic performance calibration method for the slow scanning gear of streak camera.

Description

Technical Field

[0001] This invention relates to a streak camera calibration system and method, specifically to a dynamic performance calibration system and method for the slow scan mode of a streak camera. Background Technology

[0002] A streak camera is a high-end scientific research device that possesses both high temporal and spatial resolution, enabling the conversion of temporal information into spatial information to achieve microsecond to femtosecond (10^6) resolution. -6 ——10 -15 Ultrafast imaging in the s) range has important applications in basic scientific research, major national scientific facilities and other fields.

[0003] As an ultrafast diagnostic instrument, the streak camera, based on its principle, obtains multiple time windows (scanning levels) by applying ramp voltages of different scanning speeds to the scanning plates of the streak image converter tube. For each time level, its performance characteristics need to be calibrated before use. When applying the streak camera to an ultrafast diagnostic system, dynamic performance calibration is a necessary step before application, including quantitative measurements of time resolution, the camera's full-screen time range, and dynamic range, in order to analyze experimental data.

[0004] Imaging laser pulse sequences with equal time intervals can be used to calibrate the dynamic performance of streak cameras. However, due to the inherent time delay when electrical pulses arrive at the streak camera, the electrical pulses and optical pulses cannot be synchronized, thus affecting the generation of the equal time interval laser pulse sequence. In existing technologies, for slow scan settings with time windows greater than 5 ns, the optical path can be extended to keep the optical and electrical pulse signals synchronized. However, this method is complex, typically requiring an extension of over 60 meters, resulting in excessive experimental platform space, high implementation difficulty, and significant light intensity attenuation. In actual testing, limited laboratory space makes it difficult to construct a test optical path with a sufficiently long and precise optical path difference. Summary of the Invention

[0005] The purpose of this invention is to solve the technical problems of the existing method of extending the optical path when calibrating the dynamic performance of streak cameras in slow scan mode, which is complicated, usually requires an extension of more than 60 meters, occupies too much experimental platform area, is difficult to implement, and leads to high light intensity attenuation. The invention proposes a dynamic performance calibration system and method for streak cameras in slow scan mode.

[0006] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows:

[0007] A dynamic performance calibration system for the slow scan mode of a stripe camera, which is special in that it also includes a laser, a digital time delay and a readout camera;

[0008] The laser includes a first output terminal and a second output terminal. The first output terminal outputs optical pulses, and the second output terminal outputs electrical pulses. A stripe camera is set up in the propagation optical path of the optical pulses.

[0009] The input terminal of the digital delay unit is connected to the second output terminal of the laser, and the output terminal is connected to the trigger terminal of the stripe camera. The digital delay unit is used to adjust the received electrical pulses so that the electrical pulses are synchronized with the optical pulses in the next cycle, and sends the adjusted electrical pulses to the stripe camera to trigger its operation.

[0010] The stripe camera is used to receive light pulses and convert the light pulses into equidistant stripes to generate a stripe image;

[0011] The readout camera includes an image plane composed of M×M pixels. The input end of the readout camera is connected to the output end of the stripe camera. The image plane of the readout camera reads the stripe image and converts it into a digital signal, which is then transmitted to an external computer for analysis and calculation to obtain the calibration results of the dynamic performance of the stripe camera at slow scan mode.

[0012] Furthermore, the stripe camera is in the picosecond to sub-picosecond range; the laser is a femtosecond laser that outputs light pulses with a time width of femtoseconds.

[0013] Furthermore, it also includes frosted glass, which is disposed between the streak camera and the laser to homogenize the light pulses and broaden the light pulses in the spatial direction.

[0014] This invention also provides a dynamic performance calibration method for the slow scan mode of a streak camera. Based on the above-mentioned dynamic performance calibration system for the slow scan mode of a streak camera, its special feature is that it includes the following steps:

[0015] 1) Acquire images output by the stripe camera:

[0016] 1.1) Set the repetition frequency of the laser, and the laser outputs multiple cycles of optical pulses and electrical pulses. Adjust the digital delay unit so that the dynamic stripes output by the stripe camera appear at the edge of the readout camera.

[0017] 1.2) Modify the readout camera's exposure time so that the readout camera records at least 10 light pulses;

[0018] 1.3) Start acquisition, and adjust the delay time of the digital delay unit at equal time intervals so that the dynamic stripes output by the stripe camera move at equal intervals on the readout camera image; until the exposure ends, the acquisition is complete;

[0019] 2) The dynamic performance of the stripe camera in slow scan mode is calibrated, including the calibration of time resolution and full-screen time.

[0020] A) Time resolution calibration:

[0021] Analyzing the stripe image read by the readout camera, the signal peak interval corresponding to the time delay Δt between adjacent light pulses is N pixels, and the full width at half maximum (FWHM) of the narrowest light pulse train is n pixels. Therefore, the formula for calculating the temporal resolution τ of the stripe camera is:

[0022] τ=·Δt;

[0023] The calibration of time resolution capability was completed;

[0024] B) Full-screen time calibration:

[0025] Full-screen time refers to the time range that a stripe camera can record. Based on the analysis of the stripe image read from the camera, the signal peak interval corresponding to the time delay Δt is N pixels, and the full width at half maximum (FWHM) of the narrowest light pulse train is n pixels. Therefore, the formula for calculating the full-screen time T of the stripe camera is:

[0026] T = Δt;

[0027] Where M represents the pixel in the time direction of the readout camera image plane, and the time direction refers to the direction parallel to the deflection plate of the fringe camera.

[0028] Furthermore, in step 1.1), the time window for the slow scan mode is on the order of 5 ns to us, and the repetition frequency of the laser is 1 Hz. Using a repetition frequency of 1 Hz facilitates testing and eliminates the influence of circuit jitter on the time resolution calibration.

[0029] Furthermore, in step 1.2), the exposure time is at least greater than 5 seconds.

[0030] Furthermore, in step 1.3), the digital delay unit increases the time delay Δt every 1 second, and the time delay Δt is 10 ns.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] 1. In a dynamic performance calibration system for a streak camera in slow scan mode, the light pulses output by the laser enter the streak camera to output the image. In slow scan mode, the electrical pulse signal output by the laser enters a digital delay unit. The digital delay unit adjusts the delay of the electrical pulse signal so that the adjusted trigger signal is synchronized with the light pulse. The readout camera reads and analyzes the image output by the streak camera.

[0033] 2. The present invention provides a dynamic performance calibration method for the slow scan mode of a streak camera. It eliminates the need to build an additional optical path to extend the optical path difference, thus solving the technical problems of complex optical path extension methods, excessive experimental platform space, and high light intensity attenuation. By using a digital delay device to synchronize electrical pulses and optical pulses, the inherent time delay problem of streak cameras in the slow scan mode is solved. Attached Figure Description

[0034] Figure 1 This is a connection diagram of an embodiment of the dynamic performance calibration system for slow scan mode of a stripe camera according to the present invention;

[0035] Figure 2 The image shown is the output image of a stripe camera in an embodiment of a dynamic performance calibration method for slow scan mode of a stripe camera according to the present invention.

[0036] Figure 3 This is an integral image of the output image of a stripe camera in an embodiment of a dynamic performance calibration method for slow scan mode of a stripe camera according to the present invention.

[0037] Explanation of reference numerals in the attached figures:

[0038] 1. Laser; 2. Digital time delay; 3. Frosted glass; 4. Stripe camera; 5. Readout camera; 6. Computer. Detailed Implementation

[0039] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0040] This invention provides a dynamic performance calibration system for the slow scan mode of a streak camera, such as... Figure 1 As shown, the system includes a laser 1, a digital time delay 2, a frosted glass 3, a stripe camera 4, and a readout camera 5. The digital time delay 2 and the stripe camera 4 are respectively connected to the two output terminals of the laser 1. The frosted glass 3 is placed between the stripe camera 4 and the laser 1. The readout camera 5 is connected to the output terminal of the stripe camera 4.

[0041] Laser 1 serves as the calibration light source in the calibration system, used to generate light pulses. To ensure that the performance of the calibration light source does not affect the time resolution of the streak camera 4 itself, a delta-pulse light source with finite luminous flux and infinitely narrow pulse width is generally used. The calibration light source typically refers to a light pulse duration that is much shorter than the time resolution capability of the camera under test. In this embodiment, the streak camera 4 is in the picosecond to sub-picosecond range, and a femtosecond laser with a pulse width in the femtosecond range can be used as an ideal light source for calibrating the performance of the streak camera 4.

[0042] Laser 1 includes a first output terminal and a second output terminal. The first output terminal outputs optical pulses, and the second output terminal outputs electrical pulses. The optical pulses are input to the streak camera 4 via a frosted glass 3 for imaging. The frosted glass 3 homogenizes the optical pulses, reducing damage to the streak camera 4 caused by high-energy laser spots in the optical pulses, and simultaneously widens the light spots in the spatial direction, making the image output by the streak camera 4 easier to analyze. After entering the streak camera 4, the optical pulses are converted into equidistant stripes, generating a stripe image on the fluorescent screen of the streak camera 4, which is then read by the readout camera 5. The readout camera 5 transmits and stores the image to an external computer 6 for analysis, calculating various dynamic performance parameters of the streak camera 4.

[0043] In the slow scan mode, the electrical pulse signal output by laser 1 serves as a trigger signal to activate stripe camera 4. After receiving the trigger signal, stripe camera 4 begins its scanning circuit and outputs a scanning voltage. In actual operation, stripe camera 4 typically generates an inherent time delay on the order of hundreds of nanoseconds. This inherent time delay is the "response time" inherent between the arrival of the trigger signal at stripe camera 4 and the moment when stripe camera 4 generates the scanning voltage.

[0044] If the light pulse arrives at the cathode of the streak camera 4 prematurely, and the electrical pulse signal is not modulated, the scanning voltage of the streak camera 4 will become out of sync with the light pulse. Consequently, the streak camera 4 will be unable to modulate the timing information of the light pulse, resulting in the inability to form an image. While it is possible to synchronize the light pulse with the electrical pulse signal by extending the optical path, this method is complex, typically requiring an extension of over 60 meters. This results in an excessively large experimental platform area, making implementation difficult and leading to significant light intensity attenuation.

[0045] This invention employs a digital delay unit 2 in conjunction with a laser 1 to address the asynchrony between the scanning voltage and the optical pulses of a stripe camera 4. The laser 1 has a repetition frequency, and its period is known. The electrical pulse signal from the previous cycle of the laser 1 is used to trigger the camera and record the optical pulse of the next cycle. The input of the digital delay unit 2 is connected to the second output of the laser 1, and its output is connected to the trigger terminal of the stripe camera 4. The electrical pulse signal enters the digital delay unit 2, which adjusts the signal to synchronize it with the optical pulses in the next cycle, thereby resolving the inherent time delay problem of the stripe camera 4 in slow scan modes.

[0046] Finally, the readout camera 5 captures the image from the stripe camera 4 and stores it in the computer 6. By analyzing the image information stored by the readout camera 5, the dynamic performance of the stripe camera 4 can be calculated.

[0047] This invention also provides a method for dynamic performance calibration of a streak camera at slow scan settings, specifically including the following steps:

[0048] 1) Acquire images from the stripe camera 4:

[0049] 1.1) Set the repetition frequency of the laser (1). The laser (1) outputs multiple cycles of light pulses and electrical pulses, with a period greater than the time window of the corresponding scanning position. Adjust the digital delay unit 2 so that the dynamic stripes output by the stripe camera 4 appear at the edge of the image of the readout camera 5. The time window of the scanning position is on the order of 5ns to us. In this embodiment, the repetition frequency of the laser 1 is set to 1Hz, and the first appearance of the dynamic stripes is below the image of the readout camera 5. The circuit has a certain jitter at high repetition frequency. However, the time window of the scanning position in this invention is on the order of 5ns to us, and theoretically a repetition frequency of 100kHz can be used. Therefore, in other embodiments, lasers with a repetition frequency of 100kHz or higher can also be used for testing.

[0050] 1.2) Modify the exposure time of the readout camera 5 to be at least 5 seconds so that at least 10 light pulses are recorded during the test.

[0051] 1.3) Begin acquisition, adjusting the delay time of digital delay unit 2 at equal time intervals so that the dynamic stripes output by stripe camera 4 move at equal intervals on the image of readout camera 5; since readout camera 5 maintains exposure, each movement of the dynamic stripes is recorded on the image until the exposure ends, completing the acquisition. The image acquired by readout camera 5 is as follows: Figure 2 .

[0052] In this embodiment, the digital delay unit 2 increases the time delay Δt every 1 second, and the dynamic stripes move upward a certain distance until the dynamic stripes fill the entire screen, and the acquisition ends. Figure 2 The time delay Δt is 10ns, and the full-screen time is 120ns.

[0053] 2) The dynamic performance of the stripe camera at the 4 slow scan mode is calibrated, including the calibration of time resolution and full-screen time.

[0054] A. Time resolution calibration:

[0055] The temporal resolution of the streak camera 4 refers to the smallest resolvable interval between light pulses. The calibration light source will broaden in the image captured by the streak camera 4. If two sequential light pulses enter the streak camera 4 and satisfy the Rayleigh criterion along the time axis, the time interval between these two light pulses is considered resolvable. In actual calibration and performance testing, for femtosecond laser pulses that satisfy a Gaussian distribution, their width is usually described using the full width at half maximum (FWHM). Therefore, the broadened FWHM of the calibration light source is equivalent to the smallest resolvable interval between light pulses, i.e., the temporal resolution.

[0056] In this embodiment, the time delay of the digital delay unit 2 is adjusted so that each period of light pulse has a time delay Δt relative to the previous light pulse, that is, the time interval between each light pulse is Δt. Based on the time interval between light pulses, the pulse broadening, that is, the time resolution at this level, can be obtained by analyzing the image stored in the readout camera 5.

[0057] The readout camera 5 has an image plane composed of M×M pixels. Analyzing the stripe image read by the readout camera (5), the signal peak interval corresponding to the time delay Δt between adjacent light pulses is N pixels, and the full width at half maximum (FWHM) of the narrowest light pulse train is n pixels. The formula for calculating the time resolution τ of the stripe camera 4 is:

[0058] τ=(n / N)·Δt

[0059] The calibration of time resolution capability was completed;

[0060] B. Full-screen time calibration:

[0061] Full-screen time refers to the time range that the stripe camera 4 can record; based on the stripe distance corresponding to the time delay Δt obtained in step 1), the width of the entire image of the readout camera 5 is obtained by analyzing the image stored in the readout camera 5, which is the full-screen time T of the stripe camera 4 at this setting.

[0062] The readout camera 5 has an image plane composed of M×M pixels. Based on the analysis of the stripe image read by the readout camera (5), the signal peak interval corresponding to the time delay Δt is N pixels, and the full width at half maximum (FWHM) of the narrowest light pulse train is n pixels. Therefore, the formula for calculating the full-screen time T of the stripe camera 4 is:

[0063] T = (M / N)·Δt;

[0064] Where M is the pixel value in the time direction of the readout camera's 5-image plane, and the time direction refers to the direction parallel to the deflection plate of the stripe camera.

[0065] After the stripe camera 4 is calibrated using the method of this invention, the image output by the stripe camera 4 is as follows: Figure 2 As shown. Figure 3 The image shown is an integral plot of the output image from streaky camera 4. From... Figure 2 , Figure 3 It can be seen that, Figure 2 These are images collected during actual testing. In image analysis software, after selecting a frame in the image, integration is performed over time to obtain the results. Figure 3 The integral image shown, in which Figure 3 The horizontal axis represents time, and the vertical axis represents image intensity. Figure 3 The peaks in the image represent individual light pulses, and the distance between the peaks is the time delay Δt. According to... Figure 3 The integral curve can be used to obtain dynamic performance parameters such as the temporal resolution and full-screen time range of the stripe camera 4 at this scanning level.

Claims

1. A dynamic performance calibration method for a streak camera slow scan mode, based on a dynamic performance calibration system for a streak camera slow scan mode, comprising a streak camera (4), further comprising a laser (1), a digital delay generator (2) and a readout camera (5); the laser (1) comprises a first output end and a second output end, the first output end outputs optical pulses, and the second output end outputs electrical pulses; a propagation path of the optical pulses is used to set the streak camera (4); the input end of the digital delay generator (2) is connected to the second output end of the laser (1), and the output end is connected to the trigger end of the streak camera (4); the digital delay generator (2) is used to adjust the received electrical pulses, so that the electrical pulses are time-synchronized with the optical pulses in the next cycle, and the adjusted electrical pulses are sent to the streak camera (4) to trigger its operation; the streak camera (4) is used to receive optical pulses and convert the optical pulses into equidistant fringes to generate a fringe image; the readout camera (5) comprises an image surface composed of MxM pixels, the input end of the readout camera (5) is connected to the output end of the streak camera (4), the image surface of the readout camera (5) reads the fringe image and converts it into a digital signal, which is transmitted to an external computer (6) for analysis and calculation to obtain the calibration result of the dynamic performance of the streak camera slow scan mode; characterized in that comprising the following steps: 1) collecting the output image of the streak camera (4): 1.1) setting the repetition frequency of the laser (1), the laser (1) outputs multiple cycles of optical pulses and electrical pulses, the cycle is greater than the time window under the corresponding scan mode; adjusting the digital delay generator (2) so that the dynamic fringes output by the streak camera (4) appear at the edge of the readout camera (5); 1.2) modifying the exposure time of the readout camera (5) so that the readout camera (5) records at least 10 optical pulses; 1.3) start collecting, adjust the delay time of the digital delay generator (2) at equal time intervals, so that the dynamic fringes output by the streak camera (4) move at equal intervals on the image of the readout camera (5); until the exposure is over, the collection is completed; 2) calibrating the dynamic performance of the streak camera (4) in the slow scan mode, including time resolution capability calibration and full screen time calibration; A) Time resolution capability calibration: analyze the fringe image read by the readout camera (5) to obtain the time delay Δt corresponding to the signal peak interval of N pixels between adjacent optical pulses, and the full width at half maximum of the narrowest optical pulse string is n pixels, then the calculation formula of the time resolution capability τ of the streak camera (4) is: τ = (n / N)·Δt; complete the time resolution capability calibration; B) Full screen time calibration: Full screen time refers to the time range that the streak camera (4) can record; according to the analysis of the fringe image read by the readout camera (5), the time delay Δt corresponds to the signal peak interval of N pixels, and the full width at half maximum of the narrowest optical pulse string is n pixels, then the calculation formula of the full screen time T of the streak camera (4) is: T = (M / N)·Δt; wherein M is the pixel in the time direction of the image surface of the readout camera (5), the time direction refers to the direction parallel to the deflection plate of the streak camera.

2. The dynamic performance calibration method for the slow scan mode of a streak camera according to claim 1, characterized in that: in step 1.1), the time window of the slow scan mode is in the order of 5 ns to us, and the repetition frequency of the laser (1) is 1 Hz.

3. The dynamic performance calibration method for the slow scan mode of a streak camera according to claim 2, characterized in that: in step 1.2), the exposure time is at least greater than 5 s.

4. The dynamic performance calibration method for the slow scan mode of a streak camera according to claim 3, characterized in that: in step 1.3), the digital delay generator (2) increases the time delay Δt by 10 ns every 1 s.

5. The dynamic performance calibration system for the slow scan mode of a streak camera according to claim 1, characterized in that: the streak camera is in the order of picoseconds to sub-picoseconds, and the laser (1) is a femtosecond laser, outputting light pulses with a time width of femtoseconds.

6. The dynamic performance calibration system for the slow scan mode of a streak camera according to claim 1 or 5, characterized in that: it further comprises a ground glass (3) arranged between the streak camera (4) and the laser (1) for homogenizing the light pulses and expanding the light pulses in the spatial direction.

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