JP2014173966A - Laser distance measuring device and laser distance measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure distance measuring accuracy.SOLUTION: A laser distance measuring device (10) comprises: a pulse laser beam source (12) for measuring a distance; a wavelength conversion element (14) similar to a nonlinear crystal; a light receiving section (18) which obtains reception light; a dichroic mirror (20) which separates the reception light into first and second reception light; first and second light detectors (26 and 28) which detect the first and second reception light; a level detector (34) which detects a reception level of a signal detected by the first or the second light detector; and a control section (38) which controls a temperature of the wavelength conversion element (14) on the basis of the reception level.

Description

  The present invention relates to a laser range finder, and more particularly to a pulsed laser range finder used to guide a probe to an asteroid.

  Exploration of asteroids has been planned in many countries in recent years, but the technology that can autonomously touch down asteroids far from the earth has little track record, and high accuracy and reliability are required. For this reason, it is important for a distance measuring device used for navigation guidance to maintain high accuracy over a wide distance measuring range. In addition, since the distance measuring device is a product mounted on the spacecraft, it is desirable to avoid the use of a movable portion as much as possible, and a distance measuring device having a light amount adjustment function that does not have a movable portion is expected.

  This type of pulse laser distance measuring device generally emits (transmits) a pulse laser beam (transmission pulse laser beam) toward a target and receives a pulse laser beam (reflection pulse laser beam) reflected by the target as a received pulse. Based on the measurement result of the regression time between the transmission time when the laser beam is received (received) and the transmission pulse laser beam is emitted and the reception time when the reception pulse laser beam is received, the pulse laser distance measuring device and the target It is a device that measures the distance between.

  Such a pulse laser ranging device includes a pulse laser light source such as a laser diode for emitting a transmission pulse laser beam, a transmission-side photodetector that converts the transmission pulse laser beam into a transmission electric signal, and a reception pulse laser beam. And a reception circuit that amplifies the transmission electric signal and the reception electric signal and converts them into a timing signal.

  Such a pulse laser range finder is mounted on a spacecraft for exploring asteroids. The target in this case is an asteroid. The pulse laser ranging device mounted on the spacecraft is a device used for guiding the spacecraft to the asteroid by measuring the distance between the spacecraft and the asteroid surface ranging from 50 km to 50 m. . In such a pulse laser range finder, the amount of received light varies by 6 to 7 digits depending on the distance measured. For this reason, the pulse laser ranging device has a problem that the received waveform is distorted due to saturation of the photodetector and the receiving circuit, and the ranging accuracy is deteriorated.

  For this reason, in conventional pulse laser ranging devices, the dynamics for satisfying ranging accuracy can be achieved by controlling the amplification factor of the receiving circuit according to the reception level or installing a variable filter in the transmission / reception optical path. The range is secured.

  However, in the first method of electrically changing the amplification factor of the receiving circuit, the waveform of the received signal is not only distorted but also increases noise. Furthermore, due to the characteristics of the electronic circuit elements constituting the receiving circuit, even if the temperature environment changes, the waveform of the received signal is distorted and the timing is delayed, affecting the ranging accuracy.

  On the other hand, in the second method of installing a variable filter in the transmission / reception optical path, it is necessary to mechanically drive the variable filter to change the filter density. For this reason, it is difficult to guarantee the reliability of a variable filter having a mechanical movable part in a space device that requires high reliability.

  Therefore, a third method has been proposed in which the wavelength of the transmission laser light is controlled without using a variable filter, and the light amount is adjusted by shifting the wavelength of the laser light from the center wavelength of the band-pass filter for reception (Patent Document 1). reference). In this third method, the wavelength of the pulsed laser light emitted from the laser diode is changed by controlling the temperature of the laser diode.

  However, in order to measure the distance from 50 km, a high-power solid-state laser is required as a pulse laser light source. Therefore, the third method for controlling the temperature of the laser diode as disclosed in Patent Document 1 cannot be used.

  As a method for controlling the wavelength of a solid-state laser such as a laser diode, a fourth method for mechanically controlling the angle of a nonlinear crystal using optical parametric oscillation is also known. However, in the fourth method, since the movable part has low reliability as a space device, as in the case of the variable filter, it is not suitable for use in a pulse laser range finder particularly used for assisting navigation of an asteroid explorer. Is expensive.

  In addition to this, a fifth method is also considered in which the optical system is divided into a plurality of systems and the reception level is maintained appropriately. However, in the fifth method of dividing the optical system, there is a problem in that the reception level is switched discretely and cannot cope with a continuous change in reception level.

  On the other hand, as a prior art related to the present invention, a distance measuring device using a laser device capable of outputting laser beams of two different wavelengths is known (for example, see Patent Document 2). The distance measuring device disclosed in Patent Document 2 includes a laser device, an output unit that outputs output light from the laser device to a predetermined target (target), and reflected light reflected from the target (target). A light receiving unit that receives light and a signal processing unit that calculates a distance based on an output signal of the light receiving unit. The laser device includes a laser oscillation unit that oscillates a laser beam, a fundamental wave output from the laser oscillation unit, and a conversion efficiency of the fundamental wave into a harmonic wave changes according to a temperature. A ratio control means is provided for controlling the ratio of the fundamental wave and the harmonics output from the nonlinear crystal by controlling the temperature of the nonlinear crystal.

  That is, the distance measuring device disclosed in Patent Document 2 discloses a sixth method in which the temperature of the nonlinear crystal is controlled to emit fundamental and / or harmonic laser light.

  In the distance measuring device disclosed in Patent Document 2, (1) output mode 1 for outputting the fundamental wave (1064 nm), (2) output mode 2 for outputting the second harmonic (532 nm), (3 3) It is possible to select three patterns of output modes in output mode 3 in which two waves of 50% fundamental wave and 50% second harmonic are simultaneously output. And in the distance measuring device disclosed in Patent Document 2, as a distance measurement procedure, a method of selecting whether to use a fundamental wave or a harmonic based on the received light intensity of light received by the light receiving unit, A method of selecting an output signal of the first light receiving unit or an output signal of the second light receiving unit based on the received light intensity of the first light receiving unit and the second light receiving unit is disclosed.

JP 2008-224239 A JP 2010-85316 A (FIGS. 3, 9, and 14)

  In Patent Document 2, it is selected whether to use a fundamental wave or a harmonic based on the received light intensity, or the output signal of the first light receiving unit or the output signal of the second light receiving unit is selected. Only. However, the optimum reception level cannot be maintained simply by making such a selection. As a result, it is difficult to ensure distance measurement accuracy.

  The distance measuring device disclosed in Patent Document 2 is based on the premise that the object (target) is fixed and the distance measuring device side is also fixed. That is, in Patent Document 2, the distance to the target such as atmospheric water vapor is fixed (invariant; constant). For this reason, the distance measuring device (distance measuring procedure) disclosed in Patent Document 2 cannot measure a significantly changing distance.

  In the first place, in the distance measuring device disclosed in Patent Document 2, the purpose of switching between the fundamental wave and the harmonic (switching the wavelength) is to improve the measurement resolution and to change the reflectance of the target (target). It is. In other words, in Patent Document 2, the wavelength is not switched in order to improve the ranging accuracy.

  Accordingly, an object of the present invention is to provide a laser distance measuring apparatus and a laser distance measuring method capable of ensuring (improving) distance measuring accuracy for a significantly changing distance.

The laser distance measuring device of the present invention emits a transmission pulse laser beam toward a target, receives a reflected pulse laser beam reflected by the target as a reception pulse laser beam, and transmits a transmission time when the transmission pulse laser beam is emitted. A laser distance measuring device that measures a distance to the target based on a measurement result of a regression time with respect to a reception time at which the received pulse laser beam is received,
The means for emitting the transmission pulse laser beam includes a pulse laser light source that emits a fundamental pulse laser beam, and a wavelength conversion element that converts the fundamental pulse laser beam into a second harmonic pulse laser beam. The wavelength conversion element that emits, as the transmission pulse laser beam, a pulse laser beam that has a wavelength conversion efficiency that varies depending on temperature and that is obtained by mixing the pulse laser beam of the fundamental wave and the pulse laser beam of the second harmonic. Consists of
The means for measuring the regression time includes: a transmission-side optical detector that converts the transmission pulse laser light into a transmission electrical signal; and a first reception pulse laser light and a second harmonic of the reception pulse laser light that are fundamental waves. Separating means for separating the laser beam into a second received pulse laser beam, a first reception-side photodetector that detects the first received pulse laser beam and converts it into a first received electrical signal, and the second From the second reception-side optical detector that detects the received pulse laser beam and converts it into a second received electrical signal, the transmitted electrical signal, and the first or second received electrical signal. A receiving circuit for obtaining a transmission timing at which laser light is emitted and a reception timing at which the received pulse laser light is received, and counting the regression time from the transmission timing and the reception timing, and outputting distance measurement count data A range counter unit that is composed of,
The means for controlling the temperature of the wavelength conversion element includes a temperature control unit for adjusting the temperature of the wavelength conversion element, and a level for detecting the reception level of the received pulse laser beam from the first or second received electrical signal. A detection unit and a control unit that sends a temperature control signal to the temperature control unit so that the reception level is constant.

  According to the present invention, it is possible to ensure (improve) the distance measurement accuracy of a greatly changing distance.

It is a block diagram which shows the structure of the laser ranging apparatus which concerns on 1st Example of this invention. 3 is a flowchart for explaining an operation in an approach phase of the laser distance measuring device shown in FIG. 1.

  First, features of the present invention will be described.

  The laser range finder according to the present invention is a laser range finder used for an asteroid explorer. That is, the laser range finder according to the present invention calculates the distance from the laser range finder to the asteroid by measuring the round trip time (return time) of the pulse laser, and provides navigation support for guiding the probe to the asteroid. Is a distance measuring device. The laser distance measuring device according to the present invention also has a light amount adjustment function that compensates for changes in the received light amount that changes depending on the distance and secures the distance measurement accuracy by keeping the reception level detected by the receiving circuit constant. Features.

  Next, an embodiment of the present invention will be described.

  A laser distance measuring device according to an embodiment of the present invention includes a distance measuring pulse laser light source composed of a solid-state laser, a wavelength conversion element such as a nonlinear crystal, a light receiving unit that receives received light, and a received light. A dichroic mirror that separates the first and second received lights; first and second photodetectors that detect the first and second received lights; and signals detected by the first and second photodetectors And a control unit for controlling the temperature of the wavelength conversion element based on the reception level.

  A solid-state laser used as a pulse laser light source for distance measurement emits a fundamental (1ω) pulse laser beam. The emitted pulsed laser light is incident on a wavelength conversion element such as a nonlinear crystal. The wavelength conversion element generates second harmonic (2ω) laser light from fundamental (1ω) laser light. Based on the reception level, the control unit changes the wavelength conversion efficiency of the nonlinear crystal by controlling the temperature of the nonlinear crystal, as will be described later, and continuously transmits the second harmonic (2ω) transmission laser light. Control power.

  As a result, both the fundamental wave (1ω) laser light and the second harmonic (2ω) laser light that are not converted are irradiated onto the target asteroid from the wavelength conversion element.

  After the reflected light from the surface of the asteroid is received by the optical system, it is separated by the dichroic mirror into the first received laser light of the fundamental wave (1ω) and the second received laser light of the second harmonic (2ω). The first and second photodetectors detect the first and second received laser beams, respectively.

  FIG. 1 is a block diagram showing a configuration of a laser range finder 10 according to a first embodiment of the present invention. The illustrated laser distance measuring device 10 is a laser distance measuring device that controls the amount of transmitted light and ensures distance measurement accuracy, as will be described later, in response to changes in the reception level depending on the distance measured.

  The laser distance measuring device 10 emits a transmission pulse laser beam (hereinafter also simply referred to as “transmission light”) toward a target and receives a reflected pulse laser beam reflected by the target as a reception pulse laser beam (hereinafter simply referred to as “reception”). The light source is also referred to as “light”, and based on the measurement of the regression time between the transmission time when the transmission pulse laser beam (transmission light) is emitted and the reception time when the reception pulse laser beam (reception light) is received, Measure the distance between.

  In the illustrated example, the target is an asteroid, and the laser rangefinder 10 is mounted on an asteroid explorer (not shown).

  A laser range finder 10 having a variable wavelength conversion efficiency function for controlling the amount of transmitted light includes a laser oscillator 12, a wavelength conversion element 14, a temperature control unit 16, a transmission / reception optical unit 18, a dichroic mirror 20, and a 1ω bandpass. Filter 22, 2ω bandpass filter 24, 1ω photodetector 26, 2ω photodetector 28, transmission light detector 30, reception circuit 32, level detector 34, and ranging counter The unit 36, the control unit 38, and the power supply unit 40 are configured.

  The laser oscillator 12 emits a pulsed laser beam having a fundamental wave (1ω). The wavelength conversion element 14 converts the wavelength of the pulse laser beam. That is, the wavelength conversion element 14 converts the pulse laser beam having the fundamental wave (1ω) wavelength into the pulse laser beam having the second harmonic wave (2ω) wavelength.

  More specifically, the wavelength conversion element 14 has a wavelength conversion efficiency that varies depending on temperature, and is a pulse laser obtained by mixing a pulse laser beam having a fundamental wave (1ω) and a pulse laser beam having a second harmonic wave (2ω). Light is emitted as the transmission pulse laser light (transmission light).

  Therefore, the combination of the laser oscillator 12 and the wavelength conversion element 14 serves as means for emitting transmission pulse laser light (transmission light).

  The temperature control unit 16 adjusts the temperature of the wavelength conversion element 14 as described later to vary the conversion efficiency of the wavelength conversion element 14.

  The transmission / reception optical unit 18 shapes the transmission beam and transmits the received light to the received light photodetectors 26 and 28.

  The dichroic mirror 20 separates the wavelengths of the fundamental wave (1ω) and the second harmonic wave (2ω). The 1ω bandpass filter 22 selects the wavelength of the received light of the fundamental wave (1ω). The 2ω bandpass filter 24 selects the wavelength of the received light of the second harmonic (2ω).

  Therefore, the combination of the dichroic mirror 20, the 1ω bandpass filter 22 and the 2ω bandpass filter 24 uses the received pulse laser beam (received light) as the first received pulse laser beam (first received wave) of the fundamental wave (1ω). Light) and a second receiving pulse laser beam (second received light) of the second harmonic (2ω), which functions as a separating means (20, 22, 24).

  The 1ω photodetector 26 functions as a first reception-side photodetector that detects the first received light of the fundamental wave (1ω) and converts it into a first received electrical signal. The 2ω photodetector 28 functions as a second reception side photodetector that detects the second received light of the second harmonic (2ω) and converts it into a second received electrical signal. The transmission light photodetector 30 functions as a transmission side photodetector that detects transmission light and converts it into a transmission electrical signal.

  The receiving circuit 32 amplifies the transmission and reception signals converted into these electric signals, sets a threshold value, and converts them into timing signals. The receiving circuit 32 outputs transmission / reception pulses. That is, the reception circuit 32 transmits the transmission timing of the transmission pulse laser beam (transmission beam) and the reception timing of receiving the reception pulse laser beam (reception beam) from the transmission electrical signal and the first or second reception electrical signal. And ask.

  The ranging counter unit 36 counts the time (regression time) between the transmission and reception pulses from the transmission and reception pulses from the reception circuit 32. In other words, the distance measurement counter unit 36 counts the regression time from the transmission timing and the reception timing, and outputs distance measurement count data.

  Therefore, the transmission-side photodetector 30, the separating means (20, 22, 24), the first reception-side photodetector 26, the second reception-side photodetector 28, the reception circuit 32, and the distance measurement The combination with the counter unit 36 serves as a means for measuring the regression time.

  The level detector 34 detects the level of received light. That is, the level detector 34 detects the reception level of the received pulse laser beam (received light) from the first or second received electrical signal.

  The control unit 38 calculates the optimum temperature of the wavelength conversion element 14 based on the distance (ranging count data) and the reception level, and transmits a temperature control signal to the temperature control unit 16. That is, the control unit 38 sends a temperature control signal to the temperature control unit 16 so that the reception level is constant. In response to the temperature control signal, the temperature control unit 16 adjusts the temperature of the wavelength conversion element 14.

  Therefore, the combination of the temperature control unit 16, the level detector 34, and the control unit 38 serves as a means for controlling the temperature of the wavelength conversion element 14.

  The power supply unit 40 supplies power to each unit.

  Next, the wavelength conversion element 14 of a nonlinear crystal will be described. Here, it is assumed that the laser oscillator 12 which is a solid-state laser emits YAG laser light having a wavelength of 1064 nm used for distance measurement as a fundamental wave (1ω).

In this case, the wavelength conversion element 14 can convert the YAG laser light having the fundamental wave (1ω) into laser light having a wavelength of 532 nm, which is the second harmonic wave (2ω), using a nonlinear crystal. For example, it is assumed that an LBO (LiB ₃ O ₅ ) crystal is used as the nonlinear crystal. The fundamental energy (1ω) YAG laser light has a laser energy of 109 mJ, a pulse width of 20 nsec, a beam diameter φ of 5 mm, an LBO crystal length of 20 mm, and an LBO crystal temperature of 148 ° C. To do. Under this condition, when a pulse laser beam having a fundamental wave (1ω) is incident on the LBO crystal, the laser energy of 22 mJ can be obtained from the LBO crystal at the second harmonic (2ω) wavelength of 532 nm. Here, Type I non-critical phase matching is assumed. The remaining 87 mJ remains at the wavelength of 1064 nm of the fundamental wave (1ω).

  Here, when the temperature of the LBO crystal is changed by about 2 ° C., the conversion efficiency is halved, and a laser energy of 11 mJ at a wavelength of 532 nm of the second harmonic (2ω) and 98 mJ at a wavelength of 1064 nm can be obtained. When the temperature is further changed, the conversion efficiency of the LBO crystal can be lowered. Further, the wavelength conversion efficiency can be increased by optimizing the length of the wavelength conversion element 14. By controlling the efficiency of this wavelength conversion and receiving the wavelength 532 nm of the second harmonic (2ω) and the wavelength 1064 nm of the fundamental wave (1ω) by the independent detectors 26 and 28, the optimum reception level is obtained. It is possible to control the amount of light continuously.

  Next, an outline of the operation of the laser distance measuring device 10 shown in FIG. 1 will be described.

  The fundamental wave (1ω) pulsed laser light output from the laser oscillator 12 is converted by the wavelength conversion element 14 into second harmonic (2ω) pulsed laser light. The converted second harmonic (2ω) pulse laser light is transmitted to the target as transmission light (transmission pulse laser light) through the transmission / reception optical unit 18 together with the remaining fundamental laser light (1ω). Irradiates a certain asteroid.

  As an initial value, the energy ratio between the fundamental wave (1ω) and the second harmonic wave (2ω) is set to about 10: 1, and distance measurement is performed using a pulsed laser beam of the fundamental wave (1ω) having a large energy at a long distance.

  As the spacecraft approaches the asteroid, the reception level increases and the ranging accuracy deteriorates. Therefore, when the level detection unit 34 detects that the reception level has deteriorated, the control unit 38 switches the photodetector used for ranging to the 2ω photodetector 28 to ensure ranging accuracy. To do. In the navigation guidance of the asteroid explorer, ranging accuracy is required on the near side.

  Further, the control unit 38 sends a temperature control signal to the temperature control unit 16 in order to control the optimum transmission light amount based on the reception level so that the distance becomes closer and the waveform of the 2ω photodetector 28 is not distorted. In response to the temperature control signal, the temperature controller 16 is controlled so as to adjust the temperature of the wavelength conversion element 14 and maintain an optimum reception level. Depending on the reception level kept constant, the distance measurement counter unit 36 can perform distance measurement with a certain accuracy. As a result, the spacecraft can autonomously approach the asteroid based on highly accurate distance information.

  Next, the operation in the approach phase will be described with reference to the flowchart of FIG. Here, “at the time of the approach phase” is one of the features of the present invention, in which the laser range finder 10 is mounted on a moving body such as an asteroid explorer, and a destination (target) is located several tens of kilometers away. ).

  First, the control unit 38 sets initial values (step S1). Since the initial value in the approach phase is distance measurement from a long distance, the control unit 38 performs control so that the reception circuit 32 selects the first received electrical signal having the fundamental wave wavelength (1ω) having a large output. .

  Next, the control unit 38 starts distance measurement (step S2). Subsequently, the control unit 38 acquires a distance measurement value and reception level data for each laser transmission / reception (step S3), and compares the reception levels (step S4).

  If the reception level [I] is within the upper limit specified value (a value that can ensure distance measurement accuracy) [A] that is confirmed in advance and there is no problem with the accuracy of the distance measurement value (NO in step S4), the control unit 38. Confirms the distance measurement value (step S5). If the target distance (in this case, the vicinity of the asteroid) has been reached (YES in step S5), the control unit 38 stops the distance measurement (step S14). If the target distance has not been reached (NO in step S5), the control unit 38 returns to the laser transmission / reception in step S3 and repeats this operation.

  In the comparison of the reception level in step S4, if the reception level [I] is equal to or greater than the upper limit specified value [A] (YES in step S4), the control unit 38 moves to a wavelength switching operation (step S6). ). That is, the control unit 38 selects the second received electrical signal having the second harmonic wavelength (2ω) in the receiving circuit 32.

  After wavelength switching in step S6, the control unit 38 performs laser transmission / reception again (step S7). Here, the control unit 38 checks the reception level again (step S8).

  If the reception level [I] is less than the upper limit specified value [A] and it is determined that there is no problem in ranging accuracy (NO in step S8), the control unit 38 confirms the ranging value (step S9). As before, when the distance measurement value has reached the target distance (YES in step S9), the control unit 38 stops the distance measurement operation (step S14). If the target distance has not been reached (NO in step S9), the control unit 38 returns to the laser transmission / reception operation in step S7 and repeats these operations.

  If it is determined in step S8 that the reception level [I] is equal to or higher than the upper limit specified value [A] and the distance measurement accuracy cannot be secured (YES in step S8), the control unit 38 performs an operation for changing the crystal set temperature. (Step S10). At this time, the initial value of the crystal set temperature is an intermediate value of the power of the second harmonic (2ω), and when the temperature is raised, the output of the second harmonic (2ω) is lowered and the temperature is lowered. In this case, the temperature is set in advance so that the output of the second harmonic (2ω) increases. In step S8, since the reception level [I] has already reached the upper limit specified value [A], the control unit 38 increases the crystal temperature of the wavelength conversion element 14 by a predetermined temperature of, for example, 1 ° C. The temperature control signal is sent to the temperature controller 16. This temperature change value varies depending on the design of the entire system.

  After changing the crystal temperature of the wavelength conversion element 14 in step S10, the control unit 38 performs laser transmission / reception again (step S11). Thereafter, the control unit 38 confirms the reception level [I] (step S12).

  Specifically, in step S12, the control unit 38 determines that the reception level [I] is within a certain range ([B] ≦ [I] ≦ [A] between the upper limit specified value [A] and the lower limit specified value [B]. ]). This is based on the assumption that the range of distance measurement accuracy is narrowed because distance measurement of a moving object such as an asteroid explorer requires high distance measurement accuracy as the distance decreases.

  In step S12, the control unit 38 repeats changing the crystal temperature of the wavelength conversion element 14 in step S10 so that the reception level [I] falls within the predetermined range.

  In step S10, if the reception level [I] is larger than the upper limit specified value [A], the control unit 38 sends a temperature control signal that increases the crystal temperature of the wavelength conversion element 14 by 1 ° C. To send. If the reception level [I] is smaller than the lower limit specified value [B], the control unit 38 sends a temperature control signal that lowers the crystal temperature of the wavelength conversion element 14 by 1 ° C. to the temperature control unit 16.

  Further, when the reception level [I] is within the certain range (YES in step S12), the control unit 38 confirms the distance measurement value (step S13). If the target distance has been reached (YES in step S13), the control unit 38 stops the distance measurement (step S14). When the distance measurement value does not reach the target distance (NO in step S13), the control unit 38 returns to step S11 and repeats the distance measurement operation.

  By performing such an operation, it is possible for a moving body such as an asteroid explorer to reach a target distance while ensuring distance measurement accuracy.

  The effects of the first embodiment of the present invention will be described below.

  The first effect is that high ranging accuracy can be realized by optimal reception level control. The reason is that by adopting this method, it is possible to continuously cope with a change in reception level that affects the distance measurement accuracy of the laser distance measuring device 10.

  The second effect is that a highly reliable transmission light power adjustment function that does not use a mechanical movable part can be realized. That is, a highly reliable transmission light power adjustment function can be realized without using a mechanical movable part for the optimal reception level control.

  As mentioned above, although this invention was demonstrated with reference to embodiment (Example), this invention is not limited to the said embodiment (Example). Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

  For example, in the above-described embodiment, an example in which an LBO crystal is used as a nonlinear crystal is described. However, the nonlinear crystal is not limited to an LBO crystal, and other crystals such as a KTP crystal may be used.

  INDUSTRIAL APPLICABILITY The present invention can be used for landing missions of moon and planetary probes as well as asteroid navigation guidance devices.

DESCRIPTION OF SYMBOLS 10 Laser distance measuring device 12 Laser oscillator 14 Wavelength conversion element 16 Temperature control part 18 Transmission / reception optical part 20 Dichroic mirror 22 1ω band pass filter 24 2ω band pass filter 26 1ω light detector 28 2ω light detector 30 Light for transmission light Detector 32 Receiving circuit 34 Level detection unit 36 Ranging counter unit 38 Control unit 40 Power supply unit

Claims (9)

The transmission pulse laser beam is emitted toward the target, the reflected pulse laser beam reflected by the target is received as the reception pulse laser beam, and the transmission time when the transmission pulse laser beam is emitted and the reception of the reception pulse laser beam are received. A laser distance measuring device for measuring a distance to the target based on a measurement result of a regression time with respect to time;
The means for emitting the transmission pulse laser beam is:
A pulse laser light source for emitting a fundamental pulse laser light;
A wavelength conversion element for converting the fundamental pulse laser beam into a second harmonic pulse laser beam, the wavelength conversion efficiency being different depending on temperature, and the fundamental pulse laser beam and the second harmonic pulse laser. The wavelength conversion element that emits pulse laser light obtained by mixing light as the transmission pulse laser light, and
Consisting of
The means for measuring the regression time is:
A transmission-side photodetector that converts the transmission pulse laser light into a transmission electrical signal;
Separating means for separating the received pulse laser beam into a first received pulse laser beam having a fundamental wave and a second received pulse laser beam having a second harmonic;
A first reception-side photodetector that detects the first received pulse laser beam and converts it into a first received electrical signal;
A second receiving-side photodetector that detects the second received pulse laser beam and converts it into a second received electrical signal;
A receiving circuit for obtaining a transmission timing at which the transmission pulse laser beam is emitted and a reception timing at which the reception pulse laser beam is received from the transmission electric signal and the first or second reception electric signal;
A ranging counter unit that counts the regression time from the transmission timing and the reception timing and outputs ranging count data;
Consisting of
The means for controlling the temperature of the wavelength conversion element is:
A temperature controller for adjusting the temperature of the wavelength conversion element;
A level detector that detects a reception level of the received pulse laser beam from the first or second received electrical signal;
A control unit for sending a temperature control signal to the temperature control unit so that the reception level is constant;
Laser ranging device composed of   The laser ranging device according to claim 1, wherein the control unit calculates an optimum temperature of the wavelength conversion element from the reception level and the ranging count data, and outputs the temperature control signal.   The laser range finder according to claim 1, wherein the wavelength conversion element is made of a nonlinear crystal.   The laser range finder according to claim 3, wherein the nonlinear crystal is an LBO crystal.   The laser range finder according to any one of claims 1 to 4, wherein the target is selected from a group of an asteroid, a moon, and a planet, and the laser range finder is mounted on a spacecraft. The fundamental pulse laser light emitted from the pulse laser light source is mixed with the fundamental pulse laser light and the second harmonic pulse laser light using wavelength conversion elements having different wavelength conversion efficiencies depending on the temperature. The transmission light obtained in this manner is emitted from the laser distance measuring device toward the target, the reflected pulse laser beam reflected by the target is received as reception light, and the transmission time when the transmission light is emitted and the reception light are received. A laser distance measuring method for measuring a distance between the laser distance measuring device and the target based on a measurement result of a regression time with respect to a reception time,
Starting a distance measurement using the transmission light having a predetermined energy ratio at a long distance, wherein the energy of the fundamental pulse laser light is larger than that of the second harmonic pulse laser light;
Selecting a wavelength of the received light of the fundamental wave as the received light, and confirming a first reception level of the received light of the fundamental wave;
When the first reception level is equal to or higher than an upper limit specified value, the wavelength of the second harmonic reception light is selected as the reception light, and the second reception level of the second harmonic reception light is confirmed. And steps to
When the second reception level is equal to or higher than the upper limit specified value, the step of changing the temperature of the wavelength conversion element so that the second reception level falls within a range between the upper limit specified value and the lower limit specified value. When,
A laser ranging method including:   The laser ranging method according to claim 6, wherein the predetermined energy ratio is equal to 10: 1. The step of changing the temperature of the wavelength conversion element comprises:
Increasing the temperature of the wavelength conversion element by a predetermined temperature when the second reception level becomes larger than the upper limit specified value;
Lowering the temperature of the wavelength conversion element by a predetermined temperature when the second reception level becomes smaller than the lower limit specified value;
The laser ranging method according to claim 6 or 7, comprising:   The laser ranging method according to claim 8, wherein the predetermined temperature is equal to 1 ° C.

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