JPS58111775A - Laser radar apparatus - Google Patents

Abstract

PURPOSE:To enable a heterodyne detection or homodyne detection with one pulse laser device by employing a laser beam comprising a short pulse part of high strength and a long pulse part of low strength. CONSTITUTION:A pulse laser device 1 generates a laser beam comprising a short pulse part of high strength and a long pulse part of low strength. This laser beam is divided into two parts with a beam splitter 2; one part thereof is transmitted as transmission light through a transmission optical system 3 while the other part thereof is supplied to a detector 6 as a local oscillation light via a high speed shutter 7 and a beam coupler 5. The transmission light reflected on a target is received by the receiving optical system 4 and the received light is fed to the beam coupler 5 while the local oscillation light continues thereby permitting a homodyne detection. Likewise, a heterodyne detection is possible. Thus, one pulse laser device is allowed to handle the heterodyne detection and the homodyne detection.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a laser radar device using a pulsed laser.

Conventional devices of this type emit a laser beam with a short pulse width and directly detect the reflected light from the target with a detector, measuring the propagation time of the laser beam and calculating the distance to the target from this. . By the way, it is practically important to extend the distance measurement range in this type of device, and the methods for doing so are mainly methods of increasing the laser output light intensity and NIP (NIP) of the detector.
Methods have been used to lower the noise equivalent power (Noise Equivalent Power). However, the former method requires a larger device. This has the disadvantage that there is a high probability of causing danger to the human body of the operator and the like.

On the other hand, the latter method includes the heterodyne detection method and the homodyne detection method, which can greatly improve NEP especially in the infrared region, but this method requires irradiation of the detector with laser light in addition to the received light as locally oscillated light. The disadvantage was that there were two laser devices in total.

In order to improve these drawbacks, the invention of ``1'' enables heterodyne detection or homodyne detection using a single pulse laser device.

The drawings will be explained in detail below.

FIG. 1 is a diagram showing an embodiment of the present invention.

In Fig. 1, pulsed light is generated from a pulsed laser device (]), and a beam splitter (2) and a transmission optical system (3) are used.
) is emitted toward the target as transmitted light. The transmitted light thus irradiated is reflected by the target and received by the receiving optical system (4). Although the transmitting optical system (31) and the receiving optical system (4) are shown separately in FIG. 1, they may be shared optical systems.The received light is transmitted through the beam combiner (
5) and enters the detector (6). On the other hand, a part of the pulsed light generated by the pulsed laser device (1) is separated from the transmitted light by a beam splitter (21), and passed through a high-speed shutter (7) and a beam combiner (5) as local oscillation light to the detector ( 6).If the received light is also incident on the detector (6) while the local oscillation light is incident on the detector (61), the received light can be homodyne detected.However, it is necessary to increase the measurement accuracy. If the pulse width of the laser beam is shortened for this purpose, due to the difference in the propagation time of the laser beam, if the measuring distance is long, the timing at which the locally oscillated light and the received light enter the detector will become distorted, making homodyne detection impossible. In order to prevent this, a laser beam with a pulse waveform as described below is generated. ゛Figure 2 is a diagram showing an example of the laser pulse waveform necessary for this invention. In the figure, the vertical axis represents the light intensity, and the horizontal axis represents the The axis represents time.The pulse shown in the figure is a combination of a steep pulse with very high light intensity and a long pulse with approximately constant low intensity. For convenience, the former will be referred to as a short pulse portion, and the latter will be referred to as a long pulse portion.

The method of generating such a pulse is well known, and in a Q-switched laser, the Q value of the resonator is lowered once, then the Q value is suddenly increased to generate a short pulse portion.

A long pulse portion can be created by setting the Q value high enough to continue CW light oscillation even after that.

By using pulsed light as shown in Figure 2 and making the duration of the long pulse part longer than the propagation time of the transmitting laser beam, the short pulse part of the received light can be detected with high sensitivity by homodyne detection, and the short pulse part can be detected with high sensitivity. High ranging accuracy can be obtained by shortening the pulse width. In addition, NFliP of homodyne detection
In order to lower the local oscillation light intensity, the intensity of the local oscillation light is appropriately set so that the shot noise caused by one local oscillation light becomes the dominant noise of the detector. If the intensity of the short pulse portion of the locally oscillated light is so strong that there is a risk of damaging the detector (6), the short pulse portion may be blocked using a high speed shutter (7).

Although the case of homodyne detection has been described in FIG. 1, heterodyne detection may be performed by shifting the frequency of either the transmitted light or the locally oscillated light using an acousto-optic modulation element or the like.

As described above, in the laser radar device according to the present invention,
Generate a single pulsed light consisting of a high-power short pulse part and a low-intensity long pulse part, and divide the power of the pulsed light to obtain two locally oscillated beams, and the pulse width of the long pulse part is the transmitted light. Since the locally oscillated light is maintained until the short pulse part of the received light enters the detector,
There is an advantage that by using only one pulse laser device, the received light can be subjected to highly sensitive heterodyne detection or homodyne detection without reducing the distance measurement accuracy.

[Brief explanation of drawings]

FIG. 1 shows a laser radar device according to the present invention. FIG. 2 is a diagram showing an example of a pulse waveform that is not necessary for the present invention. In the figure (11 is a pulse laser device, (2) is a beam splitter, (3) is a transmitting optical system, (4) is a receiving optical system, f5i1d
A beam combiner, (6) a detector, and (7) a high-speed shutter. Agent Shin Kuzuno −

Claims (1)

[Claims] Means for generating pulsed laser light that rises steeply and maintains a predetermined intensity for a predetermined period of time after obtaining a high peak value; means for obtaining transmitted light and local oscillation light. A laser radar device characterized by comprising means for superimposing the reflected light of the transmitted light by an object with the locally oscillated light and inputting it into a detector.