JPH04115008U - Absolute length measuring device - Google Patents

Abstract

(57) [Summary] [Purpose] N of LD excitation with wavelength tunable light source
By using a d:YAG laser, a compact and highly reliable absolute length measuring device is realized. [Structure] In an absolute length measuring device that makes a plurality of lights of different wavelengths enter a length measuring interferometer section and measures an absolute distance from a plurality of interference phases obtained from the length measuring interferometer section, the above-mentioned A laser diode-pumped Nd:YAG laser is used as a light source that emits multiple light beams with different wavelengths, and a wavelength selection element is inserted into the resonator to sequentially emit multiple oscillation wavelengths. It is characterized by a configuration that uses a light source.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

This invention is an absolute method that uses light interference to measure the absolute distance to an object. Regarding length measuring instruments, we especially use multi-wavelength lasers using Nd:YAG lasers in the light source. This enables the realization of a compact and highly reliable device.

0002

[Conventional technology]

Various reports have been made regarding absolute length measuring devices, but none have been put into practical use yet. The reason for this is that the configuration of the light source required to perform absolute length measurement becomes extremely complicated. The currently reported absolute length measuring device with an accuracy of 1 x 10 ^-7 or higher uses a CO ₂ (carbon dioxide) laser as a light source, and uses multiple wavelengths of different wavelengths in the interferometer section for length measurement. This is a length measuring device that uses the fractional method to sequentially select and inject the following lights and calculate the absolute distance from the difference in the resulting interference phases.

0003

[Problem that the idea aims to solve]

However, since CO ₂ lasers are gas lasers, they have problems such as the equipment being large, short-lived, and expensive. This point has not yet been reached.

[0004] The present invention has been made based on the problems of the prior art described above, and uses a solid-state laser Nd:YAG laser (as a laser amplification material) in the light source section of an absolute length measuring device. Compact and highly reliable absolute length measurement by using yttrium aluminum garnet _{( Y3A15O12} : _abbreviated as YAG) containing neodymium ions Nd3 ⁺ . The purpose is to provide utensils.

[0005]

[Means to solve the problem]

The configuration of the present invention to solve the above problems is to use multiple lights with different wavelengths for length measurement. Absolute distance from multiple interference phases obtained from this length measurement interferometer In an absolute length measuring device that measures The light source is a laser diode (hereinafter simply referred to as LD) pumped Nd:YAG laser. By inserting a wavelength selection element into the resonator, multiple oscillation wavelengths can be sequentially emitted. The device is characterized by a configuration that uses a multi-wavelength light source that can generate wavelengths.

[0006]

[Effect]

Previous Nd:YAG lasers were excited by flash lamps, so CO2 -It was a large device like the LD, but the output of the LD has improved in recent years. This has made LD excitation possible, resulting in a compact, highly efficient, and highly reliable light source. On the other hand, since Nd:YAG crystal is a solid, it has many oscillation lines and cannot be used as a laser beam. By placing a wavelength-tunable wavelength selection element inside the resonator, multiple waves can be It is possible to oscillate at a long distance, making it possible to realize a multi-wavelength light source for length measurement. Therefore, the present invention According to , a wavelength-tunable LD-pumped Nd:YAG laser is used as a light source. This makes it possible to downsize the device and improve reliability.

[0007]

【Example】

Hereinafter, the present invention will be explained based on the drawings. Figure 1 shows an example of an absolute length measuring device using an Nd:YAG laser as the light source of the present invention. FIG. 2 is a configuration diagram showing an example. In Figure 1, the absolute length measuring device of the present invention has multiple It is roughly divided into a wavelength light source section 1 and a length measurement interferometer section 2. The multi-wavelength light source section 1 is It is a light source that sequentially emits multiple lights with different wavelengths, and the wavelength selection element is used as a resonator. This is an LD-excited Nd:YAG laser installed inside the LD pump. In the multi-wavelength light source section 1, The light emitted from the excitation LD light source 11 driven by the LD drive constant current source 12 is coupled to The light passes through the optical system 13 and enters the Nd:YAG crystal 14. This Nd:YA The fluorescence generated in the G crystal 14 is located between the left end face and the left end face of the Nd:YAG crystal 14 in FIG. - Since a resonator is formed by the laser resonator mirror 17, laser oscillation occurs. at this time The oscillation wavelength is adjusted by adjusting the angle of the birefringence filter 15 using the wavelength tuning drive unit 16. It can be changed by The wavelengths emitted from the multi-wavelength light source section 1 in this way The light enters the length measurement interferometer section 2. The length measurement interferometer section 2 is a half mirror 2. 1 and two corner cubes 22 (for reference) and 23 (for length measurement). The interference signal is detected by the photodetector 24, and the interference phase measurement is performed. The interference phase is measured by a constant circuit 25. In the arithmetic circuit 26, the light emitted from the multi-wavelength light source section 1 is The output of the interference phase measurement circuit 25 for the multiple wavelengths of light emitted is taken in, and the absolute Calculate distance.

Next, an example of selecting an oscillation wavelength for performing absolute length measurement using the fraction method will be shown. In this case, it is important to select a laser transition that has an oscillation line with a wavelength difference required by the fraction method and has a high emission intensity. Here, FIG. 2 is an energy level diagram of Nd:YAG. ^{The 4} F _3/2 level has a long fluorescence lifetime of about 230 μs, and the 0.9 μm band ( ⁴ F _3/2 → ⁴ I _9/2 ) and the 1.06 μm band ( ⁴ F _3/2 → ⁴ I _11/2 ), strong fluorescence is observed in the 1.3 μm band ( ⁴ F _3/2 → ⁴ I _13/2 ). Among these, the 1.06 μm band has the strongest fluorescence transition. ^4F _3/2 is split into two levels, R1 and R2, by the crystal field. Furthermore, ^{the 4} I _11/2 level is divided into six levels, Y1 to Y6. FIG. 3 shows the fluorescence spectrum of Nd:YAG in the 1.06 μm band. As shown in the figure, at room temperature, the fluorescent light with a wavelength of 1.064 .mu.m from R2 to Y3 is the strongest, and therefore laser oscillation is most likely to occur at this wavelength. Table 1 shows examples of oscillation wavelengths selected in this way. By sequentially emitting the four oscillation wavelengths λ1 to λ4 shown in Table 1 and making them incident on the length measurement interferometer section 2, measuring the obtained interference phases, and calculating them in the calculation circuit 26, This enables highly accurate absolute length measurement. Qualitatively, a fractional method is used in which the combined wavelength is made smaller by increasing the frequency difference logarithmically, thereby increasing the precision of the distance that can be measured in absolute terms.

[0009]

[Table 1]

0010 Note that in the above embodiment, a birefringence filter is used as the wavelength selection element 15. However, it is not limited to this, and may be a diffraction grating, an ultrasonic optical modulator, or the like. Also , a Michelson interferometer is used as an interferometer, but Fizeau type or Mach A Zehnder type or the like may also be used.

[0011]

[Effect of the idea]

As described above in detail along with the embodiments, according to the present invention, the absolute A wavelength-tunable LD-excited Nd:YAG laser is used as a light source for a length measuring device. This makes it possible to create a compact and highly reliable absolute length measuring device.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an absolute length measuring device of the present invention.

FIG. 2 is an energy level diagram of Nd:YAG used in the light source of the device in FIG. 1;

[Figure 3] 1.0 of Nd:YAG used in the light source of the Figure 1 device
FIG. 3 is a diagram showing a fluorescence spectrum in the 6 μm band.

[Explanation of symbols]

1 Multi-wavelength light source section 2 Interferometer section for length measurement 11 LD light source for excitation 12 Constant current source for LD drive 13 Coupling optical system 14 Nd:YAG crystal 15 Birefringence filter (wavelength selection element) 16 Wavelength tuning drive unit 17 Mirror for laser resonator 21 Half mirror 22 Reference corner cube 23 Corner cube for length measurement 24 Photodetector 25 Interference phase measurement circuit 26 Arithmetic circuit

Claims (1)

[Scope of utility model registration request] Claim 1: In an absolute length measuring device that makes a plurality of lights of different wavelengths enter a length measuring interferometer section and measures an absolute distance from a plurality of interference phases obtained from the length measuring interferometer section. , a laser is attached to the light source that emits the plurality of lights with different wavelengths.
An absolute system characterized in that it uses a diode-pumped Nd:YAG laser, inserts a wavelength selection element into its resonator, and uses a multi-wavelength light source that can sequentially emit a plurality of oscillation wavelengths. - length measuring device.