A resonant cavity high-sensitivity schlieren instrument and imaging method thereof

Abstract

The present invention discloses a resonant cavity-type high-sensitivity Schlieren instrument and an imaging method thereof. The Schlieren instrument comprises an imaging device and a resonant cavity, wherein a test area is provided within the resonant cavity. When parallel light emitted by the imaging device enters the resonant cavity, the parallel light is disturbed by the test area and deflected to produce deflected light. The deflected light is then transmitted from the resonant cavity and recorded as a Schlieren image by the imaging device. The present invention aims to provide a resonant cavity-type high-sensitivity Schlieren instrument and an imaging method thereof, wherein the light beam is reflected back and forth within the resonant cavity, causing the light beam to be disturbed by the flow field multiple times, thereby increasing the light deflection angle, thereby improving the sensitivity of the Schlieren instrument and meeting the measurement requirements of low-density flow fields.

Description

Technical Field

[0001] The present invention relates to the technical field of schlieren instruments, and in particular to a resonant cavity high-sensitivity schlieren instrument and an imaging method thereof. Background Art

[0002] A schlieren instrument displays the refractive index based on the angular deflection of light passing through airflows of varying densities. It measures minute angles of light deflection. It converts changes in density gradients in the flow field into changes in relative light intensity on the recording plane, making areas of dramatic density variations, such as shock waves and compression waves in compressible flow fields, visible and resolvable.

[0003] However, in the detection of some low-density gas flow fields and low-density plasma flow fields, the sensitivity of existing schlieren detection technology is not enough to detect these low-density disturbance phenomena. Summary of the Invention

[0004] The purpose of the present invention is to provide a resonant cavity high-sensitivity schlieren instrument and an imaging method thereof, so that the light beam is reflected back and forth in the resonant cavity, so that the light beam is disturbed by the flow field multiple times, the light deflection angle is increased, thereby improving the sensitivity of the schlieren instrument and meeting the measurement of low-density flow fields.

[0005] The present invention is achieved through the following technical solutions:

[0006] A resonant cavity high-sensitivity schlieren instrument comprises an imaging device and a resonant cavity, wherein a test area is provided in the resonant cavity; when parallel light emitted by the imaging device enters the resonant cavity, the parallel light is disturbed by the test area and deflected to obtain deflected light; the deflected light is transmitted from the resonant cavity and recorded as a schlieren image by the imaging device.

[0007] Furthermore, the imaging device includes a light source, a condenser, a slit, a beam splitter, a collimating lens, a knife edge, an imaging objective lens, and a camera, wherein the light source, the condenser, the slit, the beam splitter, and the collimating lens are sequentially arranged from left to right, and the knife edge, the imaging objective lens, and the camera are sequentially arranged below the beam splitter from top to bottom;

[0008] The light beam emitted by the light source is converged at the slit by the condenser, and then transmitted to the collimating lens after being transmitted through the beam splitter. The light beam is collimated into parallel light by the collimating lens. The parallel light enters the resonant cavity and is disturbed by the test area, where it is deflected to obtain deflected light. After the deflected light is transmitted out of the resonant cavity, it is transmitted to the beam splitter through the collimating lens. After the deflected light is reflected by the beam splitter, it passes through the objective lens after being acted upon by the knife edge and reaches the camera for Schlieren image recording.

[0009] Furthermore, the resonant cavity includes a plane beam splitter and a plane reflector, the plane beam splitter and the plane reflector are sequentially arranged on the right side of the collimating lens from left to right, and a test area is provided between the plane beam splitter and the plane reflector;

[0010] After the parallel light passes through the plane beam splitter and is disturbed by the test area, the parallel light is deflected to obtain deflected light a. The deflected light a is transmitted to the plane reflector. After being reflected by the plane reflector, the deflected light a passes through the test area again. After being disturbed by the test area, the deflected light a is deflected to obtain deflected light b. The deflected light b is transmitted to the plane beam splitter. A portion of the deflected light b is transmitted out of the resonant cavity through the plane beam splitter; the other portion of the deflected light b remains in the resonant cavity after being reflected by the plane beam splitter.

[0011] Furthermore, the sensitivity of the schlieren instrument is obtained by the following formula:

[0012]

[0013] Where S represents the sensitivity, r1 represents the reflectivity of the plane beam splitter, r2 represents the reflectivity of the plane mirror, and t M Indicates the transmittance of the test area.

[0014] In this solution, the deflection angle increases each time the deflected light passes through the test area. Each complete passage through the resonant cavity (from the plane beam splitter to its return) results in a sensitivity four times higher than that of a single perturbation. Compared to traditional schlieren instruments, the schlieren instrument provided in this embodiment can generate multiple deflections within the test area. The camera records the deflected light output after multiple perturbations, thereby improving the instrument's sensitivity.

[0015] A resonant cavity high-sensitivity schlieren imaging method comprises the following steps:

[0016] S1: transmitting a beam of parallel light into a resonant cavity, wherein a test area is provided in the resonant cavity, and obtaining a beam of deflected light after the parallel light is deflected by the test area;

[0017] S2: The deflected light is transmitted to the camera after passing through the knife edge and the imaging objective lens to record the schlieren image.

[0018] Furthermore, the resonant cavity includes a plane beam splitter and a plane reflector, and a test area is provided between the plane beam splitter and the plane reflector;

[0019] After the parallel light passes through the plane beam splitter and is disturbed by the test area, the parallel light is deflected to obtain deflected light a. The deflected light a is transmitted to the plane reflector. After being reflected by the plane reflector, the deflected light a passes through the test area again. After being disturbed by the test area, the deflected light a is deflected to obtain deflected light b. The deflected light b is transmitted to the plane beam splitter. A portion of the deflected light b is transmitted out of the resonant cavity through the plane beam splitter; the other portion of the deflected light b remains in the resonant cavity after being reflected by the plane beam splitter.

[0020] Furthermore, the sensitivity of the schlieren instrument is obtained by the following formula:

[0021]

[0022] Where S represents the sensitivity, r1 represents the reflectivity of the plane beam splitter, r2 represents the reflectivity of the plane mirror, and t M Indicates the transmittance of the test area.

[0023] Working Principle: A light beam from a light source passes through a condenser and converges at a narrow slit. This beam is transformed into a small-area light source and illuminates a collimating lens, where it is collimated into parallel light. The parallel light passes through the test flow field, where it is disturbed by the flow, causing the beam to be deflected. This deflected beam then strikes a plane mirror, which reflects the deflected beam back through the test area. This deflected beam is again disturbed by the flow, increasing the beam's deflection angle. This back-and-forth process results in a sensitivity four times that of the original perturbation. After the deflected beam reaches the plane beam splitter, a small portion of the beam passes through the beam splitter and reaches the camera for Schlieren image recording. The majority of the light returns through the plane beam splitter into the test area, where it is further deflected and disturbed before being reflected back into the camera. The camera records the output light after multiple perturbations, resulting in a multiplier of the deflected light. This improves the Schlieren instrument's sensitivity.

[0024] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0025] The light beam is reflected back and forth in the resonant cavity, causing the light beam to be disturbed by the flow field multiple times, increasing the light deflection angle, thereby improving the sensitivity of the schlieren instrument and meeting the measurement of low-density flow fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0027] Figure 1 Schematic diagram of the principle of the schlieren instrument of the present invention.

[0028] Markings and corresponding parts names in the accompanying drawings:

[0029] 1. Light source; 2. Condenser; 3. Slit; 4. Beam splitter; 5. Collimating lens; 6. Knife edge; 7. Imaging objective lens; 8. Camera; 9. Plane beam splitter; 10. Plane mirror; 11. Test area. DETAILED DESCRIPTION

[0030] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with examples and drawings. The exemplary embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0031] Example

[0032] A resonant cavity high-sensitivity schlieren instrument includes an imaging device and a resonant cavity, wherein a test area 11 is provided in the resonant cavity; when parallel light emitted by the imaging device enters the resonant cavity, the parallel light is disturbed by the test area 11 and deflected to obtain deflected light; the deflected light is transmitted out of the resonant cavity and recorded as a schlieren image by the imaging device.

[0033] Specifically, if Figure 1 As shown:

[0034] The imaging device includes a light source 1, a condenser 2, a slit 3, a beam splitter 4, a collimating lens 5, a knife edge 6, an imaging objective lens 7, and a camera 8. The resonant cavity includes a plane beam splitter 9 and a plane reflector 10. The light source 1, the condenser 2, the slit 3, the beam splitter 4, the collimating lens 5, the plane beam splitter 9, and the plane reflector 10 are arranged in sequence from left to right. The knife edge 6, the imaging objective lens 7, and the camera 8 are arranged in sequence from top to bottom below the beam splitter 4.

[0035] When in use, the light beam emitted by the light source 1 passes through the condenser 2 and converges at the slit 3, so that the light beam becomes a small area light source 1 and irradiates the collimating lens 5. The collimated light is collimated into parallel light by the collimating lens 5. The parallel light passes through the plane beam splitter 94 and enters the test area 11. When the parallel light passes through the test area 11, it is disturbed by the test area 11, causing the parallel light to be deflected to obtain deflected light a. The deflected light a is irradiated on the plane reflector 10, and the plane reflector 10 reflects the deflected light a back through the test area 11. The deflected light a is disturbed by the test area 11 again. , causing the deflected light a to be deflected to obtain deflected light b, which is transmitted to the plane beam splitter 9, and a small part of the deflected light b is transmitted out of the resonant cavity through the plane beam splitter 9; the deflected light b transmitted out of the resonant cavity is transmitted to the beam splitter 4 through the collimating lens 5, and the deflected light b passes through the objective lens after being acted upon by the beam splitter 4 and the knife edge 6 to reach the camera 8 for Schlieren image recording; most of the deflected light b remains in the resonant cavity after being reflected by the plane beam splitter 9, continues to generate deflection disturbance, and then is reflected back and transmitted out of the resonant cavity through the plane beam splitter 9, and finally enters the camera 8 for Schlieren image recording.

[0036] A resonant cavity high-sensitivity schlieren imaging method comprises the following steps:

[0037] S1: A beam of parallel light is transmitted into a resonant cavity, in which a test area 11 is provided. The parallel light is deflected by the test area to obtain a beam of deflected light;

[0038] S2: The deflected light is transmitted to the camera 8 after passing through the knife edge 6 and the imaging lens 7 to record the schlieren image.

[0039] Furthermore, in this embodiment, the resonant cavity includes a plane beam splitter 9 and a plane reflector 10, and a test area 11 is provided between the plane beam splitter 9 and the plane reflector 10;

[0040] After the parallel light passes through the plane beam splitter 9 and is disturbed by the test area 11, the parallel light is deflected to obtain deflected light a. The deflected light a is transmitted to the plane reflector 10. After being reflected by the plane reflector 10, the deflected light a passes through the test area 11 again. After being disturbed by the test area 11, the deflected light a is deflected to obtain deflected light b. The deflected light b is transmitted to the plane beam splitter 9. A portion of the deflected light b is transmitted out of the resonant cavity through the plane beam splitter 9; the other portion of the deflected light b remains in the resonant cavity after being reflected by the plane beam splitter 9.

[0041] Furthermore, the sensitivity of the schlieren instrument is obtained by the following formula:

[0042]

[0043] Where, S represents the sensitivity, r1 represents the reflectivity of the plane beam splitter 9, r2 represents the reflectivity of the plane reflector 10, t M Indicates the transmittance of the test area 11

[0044] In this embodiment, the deflection angle increases each time the deflected light passes through the test area 11. A complete passage through the resonant cavity (light departing from the plane beam splitter 9 and returning to the plane beam splitter 9) results in a sensitivity four times that of the original perturbation. Compared to traditional Schlieren instrument, the Schlieren instrument provided in this embodiment can be deflected multiple times in the test area 11. The camera 8 records the deflected light output after multiple perturbations, thereby improving the sensitivity of the Schlieren instrument. When measuring low-density flow fields, the deflection angle of the light is very small, and the polarization amount is within the range of 1mm, so there is no need to consider the polarization of the light outside the field of view.

[0045] It is worth noting that due to the fast propagation speed of the light beam, when the light beam is reflected back and forth in the resonant cavity, the increase in the deflection angle each time is very small. When the light beam passes through the resonant cavity and reaches the imaging objective lens 7, the change in line width will also be relatively small. Therefore, it will not affect the sensitivity of the schlieren instrument (that is, the sensitivity of the schlieren instrument will not change with the number of times the light beam is reflected in the resonant cavity). The sensitivity mentioned in this application is 4 times that of the original single disturbance, which is compared with the traditional schlieren instrument (single disturbance).

[0046] The following describes how this solution works:

[0047] After the parallel light enters the resonant cavity, it is reflected back and forth between the plane reflector 10 and the plane beam splitter 9. After the parallel light passes through the test area 11, it is deflected at an angle of ε. The intensity of the parallel light at the camera 8 after passing through the test area 11 changes to:

[0048] (ΔI / I)0=(f / b)ε

[0049] Where f is the focal length of the collimating lens, b is the vertical width of the image of the light source at the knife edge, ΔI represents the change in light intensity, I represents the background light intensity, and (ΔI / I)0 represents the light intensity after a single disturbance.

[0050] The deflection angle after passing through the test area with a length of a is as follows:

[0051]

[0052] Where a represents the length of the test area, ε represents the deflection angle, and n represents the refractive index of the medium in the resonant cavity;

[0053] Since the plane beam splitter 9 is added to the optical path, the number of times the parallel light propagates in the resonant cavity is an even number of times the original number, and the light intensity changes are also an even number of times:

[0054]

[0055] Among them, ΔI 2l Indicates the amount of change in light intensity caused by the light beam each time it passes through the test area;

[0056] From this we can get:

[0057]

[0058] Wherein, r1 represents the reflectivity of the plane beam splitter 9, r2 represents the reflectivity of the plane reflector 10, and t M represents the transmittance of the test area 11, l represents the number of light reflections, ε 2l It represents the deflection angle of the light beam after being reflected l times in the resonant cavity; Indicates the ratio of the change in light intensity to the background light intensity.

[0059] Since light travels very fast, the change in the refraction angle of the light beam after multiple reflections in the resonant cavity is very small, so ε 2l ≈2lε;

[0060] At this time,

[0061]

[0062] Therefore, the system sensitivity factor can be expressed as:

[0063]

[0064] Where S represents sensitivity.

[0065] From the system sensitivity factor, we can see that the numerator value is greater than 1 and the denominator value is less than 1. M are all numbers less than 1, so by controlling r1, r2 and t M The specific value of can make the sensitivity factor divided by at least 10 times, 100 times to tens of thousands times of magnification, so that the system sensitivity is effectively improved.

[0066] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A resonant cavity high-sensitivity schlieren instrument, characterized in that: It comprises an imaging device and a resonant cavity, wherein a test area (11) is provided in the resonant cavity; The light source (1), condenser (2), slit (3), beam splitter (4) and collimating lens (5) of the imaging device are sequentially arranged from left to right, and the knife edge (6), imaging objective lens (7) and camera (8) of the imaging device are sequentially arranged below the beam splitter (4) from top to bottom. The light beam emitted by the light source (1) is converged at the slit (3) through the condenser (2), and then transmitted to the collimating lens (5) after being transmitted through the beam splitter (4). The light beam is collimated into parallel light by the collimating lens (5). The parallel light enters the resonant cavity and is disturbed by the test area (11) to be deflected to obtain deflected light. The deflected light is transmitted from the resonant cavity and transmitted to the beam splitter (4) through the collimating lens (5). The deflected light is reflected by the beam splitter (4), and then passes through the imaging objective lens (7) after being acted upon by the knife edge (6) to reach the camera (8) for recording a schlieren image. The resonant cavity comprises a plane beam splitter (9) and a plane reflector (10), the plane beam splitter (9) and the plane reflector (10) are sequentially arranged on the right side of the collimating lens (5) from left to right, and a test area (11) is arranged between the plane beam splitter (9) and the plane reflector (10); After the parallel light passes through the plane beam splitter (9), it is disturbed by the test area (11), and the parallel light is deflected to obtain deflected light a. The deflected light a is transmitted to the plane reflector (10). After the deflected light a is reflected by the plane reflector (10), it passes through the test area (11) again. After the deflected light a is disturbed by the test area (11), the deflected light a is deflected to obtain deflected light b. The deflected light b is transmitted to the plane beam splitter (9). A portion of the deflected light b is transmitted out of the resonant cavity through the plane beam splitter (9); the other portion of the deflected light b is reflected by the plane beam splitter (9) and remains in the resonant cavity. The sensitivity of the schlieren instrument is obtained by the following formula: Where, S represents the sensitivity, r1 represents the reflectivity of the plane beam splitter (9), r2 represents the reflectivity of the plane reflector (10), t M represents the transmittance of the test area (11).

2. A resonant cavity high-sensitivity schlieren imaging method, applied to the resonant cavity high-sensitivity schlieren instrument according to claim 1, characterized in that: The following steps are involved: S1: transmitting a beam of parallel light into a resonant cavity, wherein a test area (11) is provided in the resonant cavity, and obtaining a beam of deflected light after the parallel light is deflected by the test area (11); S2: The deflected light is transmitted to the camera (8) after being acted upon by the knife edge (6) and the imaging objective lens (7) to record the schlieren image.

3. The resonant cavity high-sensitivity schlieren imaging method according to claim 2, characterized in that: The resonant cavity comprises a plane beam splitter (9) and a plane reflector (10), and a test area (11) is provided between the plane beam splitter (9) and the plane reflector (10); After the parallel light passes through the plane beam splitter (9), it is disturbed by the test area (11), and the parallel light is deflected to obtain deflected light a. The deflected light a is transmitted to the plane reflector (10). After the deflected light a is reflected by the plane reflector (10), it passes through the test area (11) again. After the deflected light a is disturbed by the test area (11), the deflected light a is deflected to obtain deflected light b. The deflected light b is transmitted to the plane beam splitter (9). A portion of the deflected light b is transmitted out of the resonant cavity through the plane beam splitter (9); and another portion of the deflected light b is reflected by the plane beam splitter (9) and remains in the resonant cavity.

4. The resonant cavity high-sensitivity schlieren imaging method according to claim 3, characterized in that: The sensitivity of the schlieren instrument is obtained by the following formula: Where, S represents the sensitivity, r1 represents the reflectivity of the plane beam splitter (9), r2 represents the reflectivity of the plane reflector (10), t M represents the transmittance of the test area (11).

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