JPH0616244B2 - Positioning device for laser beam - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a laser beam positioning device used for irradiating a laser beam on a measurement target when measuring a physical quantity such as velocity or displacement using the laser beam. It is about.

[Prior Art] FIG. 1 is a block diagram of a conventional laser beam positioning apparatus. In the figure, (1) is a laser light source, (2) is an optical deflector,
(3) is a control circuit for the optical deflector (2), (4) is a deflected laser beam, and (5) is a photodetector.

Next, the operation will be described. A laser beam (4) emitted from a laser light source (1) is two-dimensionally scanned by a light deflector (2) in a plane where a photodetector (5) is installed. When the laser beam (4) is detected by the photodetector (5) during laser beam scanning, the photodetector (5) sends a signal to the control circuit (3) of the optical deflector (2). This allows the laser beam
(4) is positioned in the direction of the photodetector (5).

The conventional laser beam positioning device has a drawback that it takes a long time to perform the positioning because the laser beam (4) is two-dimensionally scanned to position the laser beam (4) as described above.

SUMMARY OF THE INVENTION The present invention has been made in order to eliminate the above-mentioned drawbacks of the conventional ones. Instead of two-dimensionally scanning a laser beam using an optical deflector, an optically rough surfaced object is used. An object of the present invention is to provide a laser beam positioning device that can perform positioning in a shorter time than two-dimensional scanning by diffusing a laser beam and generating an interference pattern having a two-dimensional intensity distribution.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows an example of a laser beam positioning apparatus according to the present invention. The same parts as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

In the figure, (21) is an optically rough surfaced object such as frosted glass, which is for phase-modulating the laser beam (4) from the laser light source (1) to diffusely irradiate it. Reference numeral (22) is a rotating mechanism for the rough surface object (21), and is adapted to rotate the rough surface object (21) around the point where the laser beam (4) is irradiated. (23) is a signal processing circuit for measuring the time variation of the output from the photodetector (5), (24) is the laser light source (1) or a rough surface object
(21) A block drive mechanism comprising the above signal processing circuit.
The direction of the light source (1) is changed by receiving the output from (23) so that the time variation becomes small.

The signal processing circuit (23) is, for example, as shown in FIG. 5, a DC component removing circuit (51) for removing a DC component from the output of the photodetector (5), an absolute value circuit or a square circuit ( 52)
And a smoothing circuit (53).

Next, the operation of the above configuration will be described.

A laser beam (4) emitted from a laser light source (1) is phase-modulated by a rough surface object (21) and diffused and irradiated. For this reason, on the observation surface where the photodetector (5) is placed, an interference pattern having a granular intensity distribution called a speckle pattern appears, and the rough surface object (21) is further affected by the laser beam (4).
The speckle pattern also rotates by being rotated by the rotating mechanism (22) about the point where is irradiated. The light intensity detected by the photodetector (5) is
When the laser beam (4) deviates from the center, the temporal fluctuation of the light intensity is large as shown in FIG. 3, and the fluctuation becomes smaller as it approaches the center as shown in FIG. Therefore, the time variation of the light intensity detected by the photodetector (5) is analyzed by the signal processing circuit.
Measure using (23). That is, the light intensity signal (Fig. 6 (A)) output from the photodetector (5) is a signal processing circuit.
The direct-current component removing circuit (51) of (23) removes the direct-current component as shown in FIG. 6 (B), and then inputs it to the squaring circuit (52).
The output from the squaring circuit (52) (Fig. 6 (C)) is the smoothing circuit (5
In 3), smoothing is performed as shown in FIG. 6 (D), in other words, a DC voltage proportional to the above time fluctuation is obtained. By applying this to the drive mechanism (24) as a measurement signal, the drive mechanism
(24) is the laser beam in the direction in which the above time fluctuation is reduced
Position (4).

Here, the rough surface object (21) is used to diffuse the laser beam (4) to generate an interference pattern having a two-dimensional intensity distribution, and the laser output is directed in a direction in which the temporal fluctuation of the detection output thereof is reduced. Since the emission direction of the beam (4) is controlled, the laser beam (4) can be positioned in a shorter time than the scanning time of two-dimensional scanning.

As described above, according to the present invention, the optically rough surfaced object is irradiated with the laser beam to generate an interference pattern having a two-dimensional intensity distribution, and the direction of the light source is detected from the detected output. ,
In other words, since it is configured to control the emission direction of the laser beam, there is no need to perform two-dimensional scanning with the laser beam as in the conventional case, and the nature of the interference pattern, that is, the straight line extended in the irradiation direction of the laser beam The laser beam can be positioned in a short time by utilizing the property that the interference pattern moves faster as the distance from the intersection with the plane orthogonal thereto increases.

[Brief description of drawings]

FIG. 1 is a block diagram showing a conventional laser beam positioning device, FIG. 2 is a block diagram showing an example of a laser beam positioning device according to the present invention, and FIGS. FIG. 5 is a block diagram showing a concrete configuration of a signal processing circuit in the state of large and small fluctuations, FIG. 5 (A) to (D) is a diagram of each part of the signal processing circuit. It is a signal waveform diagram. (1) …… laser light source, (4) …… laser beam, (5) …… photodetector, (21) …… optically rough surface object, (22) …… rotating mechanism,
(23) …… Signal processing circuit, (24) …… Drive mechanism. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A laser light source, an optically rough object for diffusing a laser beam from the laser light source to generate an interference pattern having a two-dimensional intensity distribution, a laser beam for the rough surface object and the interference pattern. A rotation mechanism for rotating the irradiation point of the center, a photodetector of the laser beam, and a time variation that increases as the distance from the center of the laser beam of the light intensity signal detected by this photodetector is detected, Positioning device for laser beam provided with a signal processing circuit that outputs a signal proportional to time variation, and a drive mechanism that receives a signal from the signal processing circuit and shifts the direction of the light source in a direction in which the time variation is reduced. .