JPH09179056A - Narrow laser beam transmission device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To speedily and precisely transmit a laser beam which has a small spread to a remote target body. SOLUTION: The narrow beam laser transmission device consists of a telescope direction controller, a laser device 8, a telescope 2 for transmission and an internal optical device 7, and an telescope 3 for observation, a camera 5, and a camera output image monitor for picking up an image of the target body 9 and the scattered light of the laser. The laser beam 1 is transmitted to the target body 9 by adjusting the image 14 of the target body to the position at a specific distance from the maximum intensity point 19 of a wedgelike back scattered light image on the bisector 18 of the back scattered light image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a narrow beam laser optical apparatus for transmitting a narrow beam laser having a reduced beam width toward a target at a long distance, and belongs to the technical field of optical instruments.

[0002]

2. Description of the Related Art Conventionally, transmitting a laser beam to a target has been performed in the field of spatial laser communication and the like. In many cases, the distance to the target is short and can be easily transmitted, or the spread of the laser beam is large, and the accuracy of the emission direction of the laser beam is not required in many cases. Also, if the distance to the target is long and it is necessary to transmit while narrowing the spread of the laser beam,
In general, a method of transmitting a beam to a target after increasing the beam spread, and then gradually reducing the beam spread, or a method of sequentially changing the beam direction and scanning the direction of the target object is used. Had been taken.

[0003]

However, according to the above-mentioned conventional technology, it is necessary to provide a spread control mechanism and a function for scanning, and it is necessary to complete the laser transmission with a desired power by the time. For example, when time is required and a target is moving, faster laser transmission is required. The problem to be solved is that a laser beam having a small spread is accurately and promptly transmitted to a distant target. Accordingly, it is an object of the present invention to provide a narrow beam laser transmitting apparatus capable of transmitting a narrow laser beam having a small beam width to a target at a long distance with high accuracy.

[0004]

Means for Solving the Problems When a laser beam is propagated in a medium in which a substance that scatters laser light exists, such as in the atmosphere, and the image is viewed from behind, the image of the backscattered light becomes wedge-shaped. Observable. The present invention provides
This utilizes the characteristic that the transmission direction of the laser beam can be specified from the image of the wedge-shaped scattered light. That is,
The laser transmission telescope and the observation telescope that captures the image of the scattered light of the target and the laser are installed on the same pointing control device, and the laser transmission direction is set to be able to change the micro-angle by the internal optical device. I do. The target object and the image of the scattered light of the laser beam are simultaneously imaged, and the image of the target object is located at a predetermined distance from the highest point of the scattered light intensity on the bisector of the scattered light image of the wedge-shaped laser beam. Then, the laser transmission direction is adjusted.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a narrow beam laser transmitting apparatus according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows a schematic configuration of a narrow beam laser transmission device according to the present invention. For example, a laser transmission means including a laser device 8, a transmission telescope 2 and an internal optical device 7 and a telescope pointing control device 4 are provided. And an observation telescope 3 for capturing an image of scattered light of a laser and a target located at a distance, a camera 5, and a camera output image monitor 6. Further, the transmission telescope 2 is disposed obliquely above the observation telescope 3 so that the optical axes of the two telescopes are substantially parallel. Usage is to simultaneously capture the image of the target and the scattered light of the laser beam, on the bisector of the scattered light image, so that the image of the target is located at a predetermined distance from the highest point of the scattered light intensity, Laser transmission direction to internal optical device 7
The laser beam 1 having a narrow divergence angle can be easily transmitted to the target simply by making adjustments using the laser beam, and the beam can be transmitted in a shorter time as compared with the conventional scanning system and the variable beam divergence system. The intensity of the transmitted beam varies depending on the intensity of the laser light and the type and density of the substance that generates the scattering, but transmission is possible by scanning the target image on the bisector of the scattered light image of the laser beam. Become.

FIG. 2 also shows a camera output image 13 together with a schematic configuration of a narrow beam laser transmitting apparatus that transmits laser light to the target 9. At this time, it is assumed that a medium, such as the atmosphere, in which the laser beam 1 is scattered is filled between the target 9 and the narrow beam laser transmitter.

From the target 9, it is assumed that light emitted from the target itself or light propagated from a certain light source is scattered and reflected by the target 9 and propagates in the direction of the observation telescope 3. I have. The scattering of the laser beam 1 occurs at each position on the propagation path. Here, scattered light at a distance L110 from the transmission telescope, a distance L211 from the transmission telescope, and a distance L312 from the transmission telescope will be considered. At this time, the image 14 of the target and the image 1 of the backscattered light from L1 of the laser beam 1 are displayed on the screen of the camera output image 13.
5, an image 16 of the backscattered light from L2 and an image 17 of the backscattered light from L3 can be simultaneously viewed. The distance from the transmitting telescope 2 to the point where the scattering of the laser beam 1 occurs is L
As the length becomes longer as 1, L2, L3, the image of the scattered light generated at each point on the screen becomes smaller, and the position of the image becomes closer to the image 14 of the target. The camera image when the scattered light of the laser beam 1 is actually captured is obtained by superimposing the backscattered light images at each position on the propagation path of the laser beam 1, and the scattered light image from the farthest point is defined as the top. It looks like a wedge.

FIG. 3 shows a camera output image 13 of a target image 14 and a laser beam backscattered light image 20 when actually photographed. Bisection line 1 of wedge-shaped backscattered light image
On 8 is the highest intensity point 19 of the backscattered light image. Also,
Since the propagation direction of the laser beam is on the bisector 18 of the wedge-shaped backscattered light image, the image 14 of the target is positioned on the bisector 18 of the backscattered light image, and the backscattered light is By adjusting the distance between the highest intensity point 19 of the image and the image 14 of the target, the laser beam can be transmitted to the target.

In order to determine the optimal positional relationship between the highest intensity point of the backscattered light image and the image of the target, the intensity distribution on the bisector of the backscattered light image was calculated. As shown in FIG. 4, the target 9, the laser beam 1, the observation telescope aperture 21,
The positional relationship between the camera light receiving surface 22 and the observation telescope aperture 2
The center of 1 is the origin, the Z axis is in a direction parallel to the propagation direction of the laser beam 1, the X axis and the Y axis are perpendicular, and the center of the camera light receiving surface 22 is the origin, the 原点 axis is in a direction parallel to the X axis. The η axis was set in a direction parallel to the Y axis, and geometrical optics analysis was performed.

The emission intensity of the laser beam 1 at the scattering occurrence position (x, y, z) is represented by I (x, y, z), and the backscattering coefficient by the scattering medium is represented by σb (x, y, z). A part of the backscattered light of the laser beam 1 is received by the observation telescope,
Make an image on 2. Two-dimensional intensity distribution D on the light receiving surface of this image
(ξ, η) is given by Equation 1.

[0011]

[Equation 1]

Here, T is the transmittance to the scattering occurrence point, B
(ξ, η | x, y, z) is a function representing the distribution of the scattered light image on the camera light receiving surface 22, and f is the focal length of the observation telescope. B (ξ,
η | x, y, z) is f and (x, y, z) and the observation telescope aperture 21
Is determined by the shape of B (ξ, η | x, y, z) is given by Expression 2 when represented by a pupil function A (x, y) that gives an intensity distribution at the observation telescope aperture 21.

[0013]

[Equation 2]

Σb is given by Equation 3 as the sum of the scattering coefficients σm and σa due to atmospheric molecules and aerosol taking into account only the first-order backscattering.

[0015]

(Equation 3)

Here, gm and ga are phase functions representing the angle dependence of scattering of atmospheric molecules and aerosol.

Numerical calculations were performed in the case where the target was present in outer space above the elevation angle of 48 °, and the laser beam was transmitted from the ground to the atmosphere and transmitted to the target. Assuming the US standard atmospheric model as the altitude distribution of the atmosphere, the intensity distribution on the wedge bisector of the backscattered light image of the laser beam was calculated using Equations 1, 2, and 3. FIG. 5 shows a graph of the calculation result. The horizontal axis indicates the angle from the propagation direction of the laser beam, and the vertical axis indicates the relative received light intensity. σb
Was calculated for three different values by changing the aerosol scattering ratio. Aerosol scattering ratio is large and σb is 0.1
In the case of 3σm + 0.03σa, as shown in the graph of calculation result 1, there is a maximum point near 400 μrad from the propagation direction of the laser beam, and the value of ga (π) is reduced to reduce the rate of backscattering by the aerosol. As the temperature was reduced, the distribution had the highest intensity in the range of 100 to 150 μrad from the propagation direction of the laser beam as shown in the graph of calculation result 2 and the graph of calculation result 3.

Since the state of the atmosphere changes depending on the place and time, it is necessary to adjust the positional relationship between the highest intensity point and the image of the target on the bisector of the scattered light image according to the environment in which the narrow beam laser is transmitted. There is. For example, when a laser is transmitted from the ground to a target in space such as an artificial satellite, from the calculation results in FIG. 5, the angular interval between the highest intensity point and the image of the target is determined by the scattering coefficient of the aerosol. The angle becomes one hundred to several hundreds of μrad depending on the value of 、. When the laser is actually transmitted to the artificial satellite shown in FIG. 3, the angle is about 150 μrad.

There are two methods for adjusting the positional relationship between the highest intensity point and the image of the target. In the method of operating the telescope pointing control device, the image of the target moves on the camera output image and the internal optical device Moves the image of the scattered light. Of these two methods, a convenient method may be used.

The scattering medium of the laser does not need to be filled over the entire area from the laser transmission device to the target.
It is sufficient if the scattering medium is present to a certain distance.

When the laser transmitter and the target are relatively moving, transmission can be performed with the maximum intensity by adjusting the direction in consideration of the optical path difference angle. The optical path difference angle φ is given by Expression 4 using a component v and a light speed c of the relative velocity vector perpendicular to the line of sight in the inertial system.

[0022]

(Equation 4)

By transmitting by shifting the transmission direction in the v direction by this angle, the maximum intensity is transmitted.

In this narrow beam laser transmitting apparatus, since the image of the scattered light of the laser beam is transmitted while being observed in real time, it is possible to observe the spread of the beam and the state of the aberration from the degree of blurring of the scattered light image. it can.

The field of view of the observation telescope camera is determined by the divergence angle of the beam, the distance between the optical axis of the laser transmission telescope and the optical axis of the observation telescope, and the distribution of the laser scattering medium. When transmitting a divergent laser beam, several hundred μrad is appropriate.

[0026]

As described above, the narrow beam laser transmitting apparatus according to the present invention can transmit a narrow laser beam having a small beam width to a distant target with high accuracy. Moreover, since it is suitable for laser transmission in a medium such as the atmosphere or water that scatters a laser beam, it is highly applicable. It is also convenient because the state of the laser beam can be observed during laser transmission.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a narrow beam laser transmission device used in a narrow beam laser transmission method according to the present invention.

FIG. 2 is a diagram illustrating an operation principle of a narrow beam laser transmission device by showing a camera output image.

FIG. 3 is a camera output image when a laser beam is actually transmitted using an artificial satellite as a target.

FIG. 4 is a diagram illustrating a positional relationship among a target, a laser beam, an observation telescope aperture, and a camera light receiving surface for calculating an intensity distribution on a bisector of a wedge-shaped scattered light image.

FIG. 5 is a graph in which the relative received light intensity distribution on the bisector of the wedge-shaped scattered light image is calculated with respect to the ratio of the backscattering of the three types of aerosols, with the angle from the propagation direction of the laser beam as the horizontal axis. is there.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 laser beam 2 transmission telescope 3 observation telescope 4 telescope pointing control device 5 camera 6 camera output image monitor 7 internal optical device 8 laser device 9 target 10 distance from transmission telescope L1 11 distance from transmission telescope L2 12 transmission telescope Distance L3 from camera 13 Camera output image 14 Target image 15 Backscattered light image from L1 16 Backscattered light image from L2 17 Backscattered light image from L3 18 Bisection line of backscattered light image 19 Highest intensity point of backscattered light image 20 Backscattered light image of laser beam 21 Observation telescope aperture 22 Camera light receiving surface L1 Distance from transmission telescope L2 Distance from transmission telescope L3 Distance from transmission telescope X Distance from observation telescope aperture Coordinate axis taken perpendicular to laser beam propagation direction with center as origin Y perpendicular to laser beam propagation direction and perpendicular to laser beam propagation direction with center of observation telescope aperture as origin Coordinate axes taken in different directions Z Coordinate axes taken in the direction parallel to the propagation direction of the laser beam with the origin at the center of the observation telescope aperture ξ Coordinate axes parallel to the X axis with the origin at the center of the camera light receiving surface η Camera light receiving surface原点 b (x, y, z) Backscattering coefficient due to scattering medium at scattering position σm Scattering coefficient due to atmospheric molecules σa Scattering coefficient due to aerosol

Claims (1)

[Claims] 1. A laser light transmitting means facing a target to be transmitted of laser light through a medium in which a substance that scatters laser light exists, and a light parallel to an optical axis of the laser light transmitting means. An observation telescope arranged to have an axis, and the pointing directions of both optical axes can be changed without giving a relative change between the optical axis of the laser light transmitting means and the optical axis of the target and the observation telescope. A pointing direction changing means, wherein a wedge-shaped image of the scattered light of the laser beam transmitted from the laser light transmitting means is obtained by the observation telescope, and the wedge-shaped image is obtained by the pointing direction changing means. By adjusting the transmission direction of the laser so that the image of the target is located at a predetermined position determined by the state of the scattering medium with reference to the highest light intensity point on the branch line, the narrow beam laser is adjusted to the target. Narrow beam laser transmission device and transmits.