CN117928897A - Device and method for synchronously measuring time of converging short pulse light beams by large included angles - Google Patents
Device and method for synchronously measuring time of converging short pulse light beams by large included angles Download PDFInfo
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- CN117928897A CN117928897A CN202410054188.1A CN202410054188A CN117928897A CN 117928897 A CN117928897 A CN 117928897A CN 202410054188 A CN202410054188 A CN 202410054188A CN 117928897 A CN117928897 A CN 117928897A
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- 230000003287 optical effect Effects 0.000 claims abstract description 7
- 230000001360 synchronised effect Effects 0.000 claims description 6
- 239000000463 material Substances 0.000 claims description 4
- 230000005540 biological transmission Effects 0.000 claims 1
- 238000000691 measurement method Methods 0.000 claims 1
- 238000005259 measurement Methods 0.000 abstract description 12
- 230000008685 targeting Effects 0.000 abstract description 4
- 238000010586 diagram Methods 0.000 description 3
- 238000005305 interferometry Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
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- 238000004458 analytical method Methods 0.000 description 1
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- 238000002474 experimental method Methods 0.000 description 1
- 239000005350 fused silica glass Substances 0.000 description 1
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Abstract
The device comprises a short pulse light beam, a focusing system, a projection reflector, a prism and a camera, wherein the short pulse light beam respectively reaches a target point after being converged by the focusing system and reflected by the projection reflector in sequence during targeting, and each light beam passing through the projection reflector is converged at the target point; the angle bisector of the included angle of the optical axes of the two short pulse beams to be tested in time synchronization is taken as a system symmetry axis, the system symmetry axis is moved into a prism positioned between a projection reflector and a target point, the cross section of the prism is an isosceles triangle, and the angle of the projection reflector is adjusted, so that the short pulse beams respectively enter from the inclined plane of the isosceles prism and exit from the bottom surface, and reach the target point after being deflected by the prism; and (3) moving into the camera to enable the light sensitive surface to coincide with the target point and the normal line to coincide with the symmetry axis of the system, recording interference fringes generated by the two beams of light, and judging the time synchronization condition of the two beams of light according to the contrast ratio of the interference fringes. And the time synchronization measurement of the short pulse light beams converged at the included angle between the large beams is realized.
Description
Technical Field
The invention belongs to the technical field of laser, in particular to a device for measuring time synchronization among short pulse beams which are arranged in a converging way at an included angle between large beams; the invention relates to time-synchronous adjustment of short pulse beams.
Background
In the technical field of ultra-short laser, in order to obtain higher peak power density at a target point, besides improving the peak power density of the target point by adopting methods of improving energy, compressing pulse width and reducing focused focal spot, the realization of multi-beam time domain and space domain superposition targeting is also an effective means for improving the peak power density of the target point.
For a multi-beam super-strong ultrashort laser system, pulses cannot reach a target at the same time due to various reasons, and the effect of increasing the peak power density of the target cannot be achieved. For the pulse with longer pulse width, the delay between pulses of different light paths is generally measured by configuring a high-speed oscilloscope, a stripe camera and the like at a target point, but the time delay measurement precision with the precision of a plurality of picoseconds is realized at most due to the performance limitation of measurement equipment; the time delay measuring precision with higher precision can be realized by an interferometry, and the time delay measuring by the interferometry needs to determine the time delay amount between light beams by observing the contrast of interference fringes by a high-resolution camera. In engineering application, for converging short pulse light beams with large included angles among beams, due to larger beam interval, interference fringes obtained at a target point after focusing have larger density, and a general camera cannot distinguish such dense fringes, so that fringe contrast cannot be observed, and the scheme cannot be applied.
Disclosure of Invention
The invention aims to provide a device for synchronously measuring the time of converging short pulse light beams with large included angles among beams, wherein a prism is added as a light beam deflection mechanism before the light beams reach a target point, so that the included angles among the converging short pulse light beams reaching the target point are reduced, interference fringes which can be resolved by a common camera are obtained, and further, the time synchronization measurement of the converging short pulse light beams with large included angles among the beams is realized. The device has simple structure and low cost, is easy for engineering realization, and can realize precise synchronous measurement between beams without greatly changing the prior device.
In order to achieve the above object, the technical solution of the present invention is as follows:
A time synchronization measuring device for converging short pulse light beams with large included angles between beams is characterized in that: the device comprises a short pulse beam, a focusing system, a projection mirror, a prism and a camera. In actual targeting, the short pulse light beams are converged by the focusing system and reflected by the projection reflector in sequence and then reach the target point, and each light beam passing through the projection reflector is converged on the target point. The angular bisector of the included angle of the optical axes of the two short pulse beams with synchronous time to be measured is the symmetry axis of the system. When time synchronization measurement is carried out, a prism positioned between the projection reflector and the target point is moved in, the cross section of the prism is isosceles triangle, and the angle of the projection reflector is adjusted, so that short pulse light beams respectively enter from the inclined plane of the isosceles prism and exit from the bottom surface, and reach the target point after being deflected by the prism; and (3) moving into the camera to enable the light sensitive surface to coincide with the target point and the normal line to coincide with the symmetry axis of the system, recording interference fringes generated by the two beams of light, and judging the time synchronization condition of the two beams of light according to the contrast ratio of the interference fringes.
The short pulse beam comprises at least two beams, and each beam for measuring the time delay between beams comprises only two beams.
The bottom surface of the prism is parallel to the photosensitive surface of the camera, and the top edge line is positioned on the symmetry axis of the system and is perpendicular to the central optical axes of the two converging light beams.
Adjusting the angle of a projection reflector 3 corresponding to one incident beam, so that the incident beam is deflected to the other incident beam and enters from an inclined plane of the prism, which is close to one side of the other incident beam; the other incident beam is adjusted in the same way.
The prism is designed by combining the working wavelength, the base material and the working angle, so that the deflection quantity of the two incoming light beams is ensured to just enable the two light beams to be converged to the target point.
When the contrast of the facula stripe recorded by the camera is strongest, the complete time synchronization between the two converging light beams is shown; and when the fringe contrast is weak, a certain time delay exists between the two converging light beams.
The invention has the following technical effects:
1) The method comprises the steps of adding a beam deflection mechanism before a beam reaches a target point, reducing the included angle between the large included angles of the beams reaching the target point and converging short pulse beams, and obtaining interference fringes which can be resolved by a common camera, so that the time synchronization measurement of the short pulse beams converged by the large included angles between the beams is realized.
2) The prism is designed to serve as a beam deflection mechanism, and the beam deflection mechanism and the projection reflector are matched with each other in adjusting angle, so that two beams to be detected output by the prism are converged to a target point after being deflected, and a reduced included angle between the beams to be detected is obtained.
3) The device has simple structure and low cost, is easy for engineering realization, and can realize precise synchronous measurement between beams without greatly changing the prior device.
Drawings
FIG. 1 is a schematic diagram of a device for synchronously measuring the time of converging short pulse beams with a large included angle between beams
1-Short pulse beam; a 2-focus system; 3-a projection mirror; 4-prisms; 5-camera; 6-target point; 7-converging the light beams with a large included angle; 701-a first converging light beam; 702-a second converging light beam; 8-system symmetry axis; 9-converging the light beam in a test state; 901-converging the light beam in a first test state; 902-the second test state converges the light beam.
FIG. 2 is a schematic diagram showing interference fringe analysis of a device for synchronously measuring the time of converging short pulse beams with a large included angle between beams
Detailed Description
The invention is further illustrated in the following examples and figures, which should not be taken to limit the scope of the invention.
Examples:
fig. 1 is a schematic diagram of a device for synchronously measuring the time of converging short pulse beams at an included angle between large beams, which is shown in the drawing, and comprises a short pulse beam 1, a focusing system 2, a projection reflector 3, a prism 4 and a camera 5. In actual targeting, the short pulse light beams 1 are converged by the focusing system 2 and reflected by the projection reflector 3, then reach the target point 6, and the converging light beams 7 with included angles between the large beams passing through the projection reflector 3 are converged on the target point 6. The two beams to be measured in time synchronization are a first converging beam 701 and a second converging beam 702 respectively, and the angular bisector of the included angle of the optical axes of the two beams is the system symmetry axis 8. When time synchronization measurement is carried out, the prism 4 positioned between the projection reflector 3 and the target point 6 is moved in, the section of the prism 4 is isosceles triangle, and the angle of the projection reflector 3 is adjusted so that the first converging light beam 701 and the second converging light beam 702 respectively enter from the inclined plane of the isosceles prism and exit from the bottom surface, and reach the target point 6 after being deflected by the prism; the camera 5 is moved in to enable the photosurface to coincide with the target point 6, the normal line of the photosurface coincides with the symmetry axis 8 of the system, interference fringes generated by two beams of light on the photosurface of the camera 5 are recorded, and the time synchronization condition of the two beams of light is judged according to the contrast ratio of the interference fringes.
The short pulse beam 1 comprises at least two beams, of which only two beams each time are used for measuring the time delay between the beams.
The bottom surface of the prism 4 is parallel to the light sensing surface of the camera 5, and the top edge line of the prism 4 is positioned on the symmetry axis of the system and is perpendicular to the central optical axes of the first converging light beam 701 and the second converging light beam 702.
Adjusting the angle of the projection mirror 3 corresponding to the incident light beam 701 so that the incident light beam 701 is deflected to the incident light beam 702 to become an incident light beam 901, and the incident light beam 901 is incident from the prism 4 near the inclined plane of the incident light beam 702; the angle of the projection mirror 3 corresponding to the incident light beam 702 is adjusted so that the incident light beam 702 is deflected to the incident light beam 701 to become an incident light beam 902, and the incident light beam 902 is incident from the prism 4 near the inclined surface of the incident light beam 701.
The prism 4 needs to be designed by combining the working wavelength, the base material and the working angle, and the deflection amount of the two incoming light beams needs to be ensured to just ensure that the converging point of the two light beams 1 reaches the target point 6. Assuming that the refractive index n, the vertex angle 2 omega of the prism 4 under the working wavelength, the included angle alpha between the incident beam 901 and the symmetry axis of the system after the angle adjustment of the projection reflector, and the included angle delta between the target beam emitted from the bottom surface of the prism and the symmetry axis of the system are as follows:
By designing the angle of adjustment of the prism 4 and the projection mirror 3, the angle between the two light beams incident on the target point 6 can be reduced.
When the contrast of the light spot stripe recorded by the camera 5 is the strongest, the first converging light beam 701 and the second converging light beam 702 are completely time-synchronized; when the fringe contrast is weak, it indicates that there is a certain time delay between the first converging light beam 701 and the second converging light beam 702.
The working principle of the device is described as follows.
Two short pulse beams are illustrated as an example. The short pulse light beams are converged by the focusing system and reflected by the projection reflector in sequence and then reach the target point, and in some physical experiments, two short pulse light beams are required to reach the target point at the same time. However, due to insufficient mounting accuracy, beam jitter, and the like, two short pulses cannot reach the target at the same time. The time synchronization of the two beams is typically measured directly by configuring a time measurement module at the target point, e.g., an oscilloscope, a streak camera. For ultra-short pulses with pulse widths not exceeding a few picoseconds, time synchronization accuracy to sub-picosecond accuracy is generally required, whereas typical measurement means cannot resolve such high time delays. It is therefore necessary to carry out time-synchronized measurements by indirect methods, one of which is interferometry.
When the two beams are time-synchronized, the two beams can be equivalently regarded as two sub-apertures of the same beam, a double-beam interference pattern is obtained at the target point, and the fringe contrast ratio is generally higher. If the two light beams are not synchronous in time, the two light beams are partially overlapped or not overlapped at all in time domain, and the image recorded by the target point has small contrast or no interference fringes at all. Therefore, the time synchronization condition of the double light beams can be judged through the contrast ratio of the interference fringes, and the time synchronization of the double light beams is indicated when the contrast ratio of the interference fringes is the strongest, otherwise, the time synchronization of the double light beams is indicated to have considerable time delay.
However, when the included angle between the two light beams is larger, the fringe density is larger and exceeds the resolution limit of the camera. At this time, even if the two light beams are completely time-synchronized, the camera can only record the light spot without interference fringes, and it cannot be judged whether the two light beams are time-synchronized. According to the device for measuring the time synchronization of the converging short pulse light beams with the included angles between the large beams, provided by the invention, the included angles between the two converging light beams with the included angles between the large beams before reaching a target point are reduced by introducing the prism, so that sparse interference fringes are obtained during the time synchronization of the double light beams, the interference fringes can be directly recorded by a camera, and the time synchronization condition of the double light beams is judged through the contrast ratio of the interference fringes.
And the two light beams with the included angle theta and the central wavelength lambda interfere at the target point when the time of the two light beams is synchronous. The beam wave vector direction of the beam at the target point is along the beam axis direction, and the converging system has a certain focal depth, so that the converging system can be equivalent to parallel beams for approximate treatment when analyzing the interference fringe density, and the following relation is satisfied according to the geometrical relation as shown in fig. 2, the interference fringe interval delta: :
Taking an included angle θ between two beams of light as 30 °, the central wavelength λ of the beam of light is 1.053 μm as an example, and the corresponding fringe interval Δ=2.03 μm. The pixel size of a typical camera for light beams is at least about 2 μm (e.g., 1.85 μm for the camera chip Sony IMX2 26), so the camera cannot capture interference images; the fringe spacing is close to the laser wavelength, and the fringe spacing of 2.03 μm cannot be resolved by the optical amplification system.
According to formula (2), the method for effectively increasing the fringe spacing is to reduce the included angle theta between the two beams of light. The invention relates to a time synchronization measuring device for converging short pulse light beams with a large included angle, which reduces the included angle between two converging light beams with the large included angle before reaching a target point by introducing a prism. Taking a prism material as fused silica (refractive index n=1.45), taking a prism vertex angle 2ω=120° as an example, when adjusting the projection mirror 3 to make the incident light beams 901 and 902 form an included angle α=14° with the symmetry axis of the system, according to formula (1), it can be known that the included angle between the two light beams to be measured after being deflected by the prism 4 is 2δ=4°, according to formula (3), the corresponding fringe interval Δ=15.1 μm, and interference fringes can be directly recorded by a camera with a pixel size of about 1.85 μm.
Claims (4)
1. A time synchronous measuring device for converging short pulse beams with a large included angle between beams comprises a short pulse beam 1, a focusing system 2 and a projection reflector 3; the two short pulse light beams 1 are respectively converged by the focusing system 2 and reflected by the projection reflector 3 to reach the target point 6. The converging light beams 7 with the included angles between the large beams passing through the projection reflector 3 are converged on the target point 6, the two light beams with the time synchronization to be detected are the first converging light beam 701 and the second converging light beam 702 respectively, and the angular bisector of the included angles between the optical axes of the first converging light beam 701 and the second converging light beam 702 is a system symmetry axis 8, which is characterized in that:
A prism 4 disposed between the projection mirror 3 and the target point 6, wherein the cross section of the prism 4 is isosceles triangle, the vertex of the isosceles triangle coincides with the system symmetry axis 8, and the base of the isosceles triangle is perpendicular to the system symmetry axis 8;
a camera 5, wherein the light sensitive surface of the camera 5 coincides with the target point 6 and the normal line coincides with the system symmetry axis 8;
By adjusting the angle of the projection mirror 3, the first converging light beam 701 and the second converging light beam 702 respectively enter from the inclined plane of the prism and exit from the bottom surface of the prism, the light beams are deflected to the target point 6 by the prism to generate interference fringes, collected by the camera 5 and transmitted to the computer, and the time synchronization condition of the two light beams is judged according to the contrast ratio of the interference fringes.
2. The device for synchronously measuring the time of converging short pulse light beams with the included angles between large beams according to claim 1, wherein the prism is used as a light beam deflection device, the angles of incident light and emergent light meet the law of refractive index, and the included angles between two light beams reaching a target point are reduced by matching the materials of the prism, the refractive index, the angle of a vertex angle, the position of a bottom surface and the adjustment angle of the projection reflector 3, so that the two light beams are converged to the target point.
3. The device for measuring the time synchronization of the converging short pulse beams with the included angles between the two converging beams according to claim 1, wherein the device is characterized in that the full time synchronization between the two converging beams is represented when the contrast of the light spot stripes recorded by the camera is strongest; and when the fringe contrast is weak, a certain time delay exists between the two converging light beams.
4. The time synchronization measurement method for converging short pulse light beams with large included angles between beams is characterized by comprising the following steps:
S1, sequentially placing a focusing system 2 and a projection reflector 3 along the light path transmission direction; the two short pulse light beams 1 are converged by the focusing system 2, reflected by the projection reflector 3 and then reach the target point 6, and converged by the converging light beam 7 with the included angle between the large beams of the projection reflector 3 and converged on the target point 6;
S2, selecting a prism 4, wherein the cross section of the prism 4 is an isosceles triangle, the vertexes of the isosceles triangle are coincident with the system symmetry axis 8, and the bottom sides of the isosceles triangle are perpendicular to the system symmetry axis 8;
S3, moving the prism 4 between the projection reflector 3 and the target point 6, and adjusting the angle of the projection reflector 3 to enable the first converging light beam 701 and the second converging light beam 702 to respectively enter from the inclined plane of the isosceles prism and exit from the bottom surface, and reach the target point 6 after being deflected by the prism;
S4, moving the camera 5 to the target point 6, enabling the photosurface of the camera 5 to coincide with the target point 6 and enabling the normal line of the photosurface of the camera 5 to coincide with the system symmetry axis 8, recording interference fringes generated by two beams of light on the photosurface of the camera 5, and judging the time synchronization condition of the two beams of light according to the contrast ratio of the interference fringes.
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