JPH08102564A - Wavelength conversion laser device - Google Patents

Abstract

(57) [Summary] [Object] To provide a wavelength conversion laser device which has a stable output light intensity, a low noise output, and a single mode spectrum. A laser beam emitted from a semiconductor laser 1 is collimated by a collimator lens 2 and then converged by a focusing lens 3 to excite a solid-state laser medium 4, and the solid-state laser medium 4 is arranged in a Fabry-Perot resonator. Therefore, laser oscillation occurs. At this time, the second harmonic is generated in the nonlinear optical crystal 5 similarly arranged in the resonator, and the green laser of 532 nm which is the second harmonic of the Nd: YAG1064 nm laser is oscillated. Then, by adjusting the substrate angles of the parallel-plane substrates 7 and 8 having different thicknesses to match the mode with the gain, a laser output of a single mode spectrum can be obtained with low noise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength conversion laser device which can be used as a light source in, for example, optical communication, optical measurement, optical memory or color display.

[0002]

2. Description of the Related Art As a wavelength conversion laser device, a solid-state laser medium and a Fabry-Perot resonator in which a nonlinear optical crystal is disposed are used to construct a wavelength conversion laser device by utilizing the second harmonic generated in the nonlinear optical crystal. There is a conversion method, and since the wavelength of the infrared region or red laser light emitted from a YAG laser or the like can be converted by a non-linear optical crystal to obtain a green or blue short wavelength laser light, such a wavelength is used. If the conversion laser device is used as a laser disk or a light source for optical communication, the effect of improving recording density and communication capacity can be expected.

A conventional wavelength conversion laser device constructed by using a Fabry-Perot resonator having the solid-state laser medium and a nonlinear optical crystal arranged therein will be described with reference to FIG.

FIG. 9 shows a conventional wavelength conversion laser device which oscillates a green laser of 532 nm, and includes a semiconductor laser 1 having a wavelength of 810 nm as an excitation light source, a collimator lens 2, a focusing lens 3, and a solid laser medium 4. The output mirror 6 constitutes a Fabry-Perot resonator together with the end face, the solid-state laser medium 4 and the nonlinear optical crystal 5 arranged in the resonator. Here, the semiconductor laser is used as the excitation light source because it generates less heat and can be significantly downsized as compared with the case where a lamp is used as the excitation light source, and is advantageous in terms of reliability and life. The solid laser medium 4 has a width of 10 m, for example.
The Nd: YAG crystal of m is K as the nonlinear optical crystal 5.
TP (KTiOPO ₄ ) crystal is used.

In this wavelength conversion laser device, the laser light emitted from the semiconductor laser 1 is collimated by the collimator lens 2 and then converged by the focusing lens 3 to excite the solid laser medium 4. Since this solid-state laser medium 4 is arranged in a Fabry-Perot resonator consisting of one end face of the solid-state laser medium 4 and the output mirror 6, laser oscillation occurs when excited. At this time, the second harmonic is generated in the nonlinear optical crystal 5 similarly arranged in the resonator, and the green laser of 532 nm which is the second harmonic of the Nd: YAG1064 nm laser is oscillated. As a result, wavelength conversion is performed, and the short-wavelength laser light passes through the output mirror 6 and is output to the outside of the laser device.

At this time, the wavelengths of 810 nm, 1064 nm and 532 nm are respectively present on the respective crystal and output mirror surfaces.
On the other hand, the coating of the high reflection film and the low reflection film is applied as follows. Note that-is irrelevant and may have any reflectance.

[0007]

[Table 1]

Although the conventional wavelength conversion laser device is constructed as described above, such a wavelength conversion laser device is
The fundamental principle is to oscillate the spectral region where stimulated emission occurs using an optical resonator, and only when a standing wave is present in the optical resonator in the gain region of stimulated emission,
A phenomenon called laser oscillation occurs. Since the laser gain region is larger than the spacing of the standing waves that normally exist in the resonator, multimode oscillation occurs, and multiple fundamental wave modes exist in the resonator, and their harmonics occur. There is a problem that the second harmonic is modulated and causes noise. That is, the wavelength conversion laser device of FIG. 9 exhibits a spectrum as shown in FIG. 10, the half width is about 0.2 nm, and a plurality of oscillation lines considered to be longitudinal modes are observed.

Therefore, it has been proposed to arrange the etalon in the Fabry-Perot resonator to provide a single longitudinal mode.

As shown in FIG. 11, an etalon is a type of wavelength filter in which both end faces of a single plate are highly accurately maintained in parallelism and both sides are partially transparent coated. The frequency interval at which the transmittance is maximum, that is,
The free spectrum interval (wavelength interval in which modes can exist) is expressed by the following equation.

Δν = C ₀ / 2nlcosθ where C ₀ is the speed of light in vacuum, n is the refractive index of the plane plate,
l is the thickness of the plane plate, and θ is the incident angle of light incident on the plane plate.

[0012]

As described above, by disposing the etalon in the Fabry-Perot resonator,
Although noise can be reduced, for example, when a parallel plane substrate with a thickness of 1 mm is used as the etalon, 1064n
The free spectrum interval near m is 0.39 nm.
Therefore, when the substrate angle is adjusted to match the gain peak, for example, 1064.3 nm, 1063.91.
, And modes exist near 1064.69 nm, and the spectrum of the oscillation laser is as shown in FIG. As described above, in the case of one 1 mm thick substrate, side peaks often exist, and in this state, the side peak becomes large or small, and the fluctuation makes the output unstable. There is a problem that it is difficult to stabilize.

The present invention has been made in view of the above circumstances, and has a stable output light intensity, a low noise output, and a wavelength conversion laser device capable of converting a spectrum into a single mode. The purpose is to provide.

[0014]

To achieve the above object, the wavelength conversion laser device of the present invention will be described with reference to the embodiment of the present invention shown in FIG. In a wavelength conversion laser device configured using a Fabry-Perot resonator having a solid-state laser medium 4 and a nonlinear optical crystal 5 arranged therein, a plurality of etalons 7 and 8 having different widths are arranged in the resonator. And

[0015]

[Operation] 1mm thickness and 0.5m as etalon with different width
1064 nm when using two parallel flat substrates of m thickness
The respective free spectrum intervals (wavelength intervals in which modes may exist) in the vicinity are 0.39 nm and 0.78 nm. When only the 0.5 mm thick substrate is placed in the Fabry-Perot resonator, the free spectrum interval of the 0.5 mm thick substrate is 0.78 nm, so if the mode is adjusted to the gain by adjusting the substrate angle, the oscillation spectrum Is as shown in FIG. 2, and no side peak occurs. This gives 0.5
One mode can be used with one mm-thick substrate, but with only one 0.5 mm-thick substrate, the multi-mode is obtained as shown by the oscillation spectrum in FIG. This is because the longitudinal modes exist at intervals of around 0.04 nm,
This is because, as shown in FIG. 3, since the line width of the transmission curve of one 0.5 mm thick substrate is large, there are multiple longitudinal modes of the resonator. On the other hand, the transmission curve of a 1 mm thick substrate has a narrow line width as shown in FIG. Therefore, stable single-mode oscillation can be achieved by combining a 1 mm thick substrate in which the generation of longitudinal modes is small and a 0.5 mm thick substrate in which side peaks are small.

[0016]

Embodiments of the wavelength conversion laser device of the present invention will be described below.

FIG. 1 shows an embodiment of a wavelength conversion laser device which oscillates a green laser of 532 nm, which comprises a semiconductor laser 1 having a wavelength of 810 nm as an excitation light source, a collimator lens 2, a focusing lens 3 and a solid laser medium 4. Mirror 5 forming a Fabry-Perot resonator together with one end face, and a width of 10 mm arranged in the resonator
9 of the solid-state laser-medium 4 and the nonlinear optical crystal 6 of FIG.
1 mm thick uncoated parallel plane substrate as an etalon and 0.5
An uncoated parallel plane substrate 8 with a thickness of mm is added.

In this wavelength conversion laser device, the laser light emitted from the semiconductor laser 1 is collimated by the collimator lens 2 and then converged by the focusing lens 3 in the same manner as the wavelength conversion laser device of FIG. Since the medium 4 is excited and the solid-state laser medium 4 is arranged in the Fabry-Perot resonator, laser oscillation occurs. At this time, the second harmonic is generated in the nonlinear optical crystal 5 similarly arranged in the resonator, and Nd: YAG1
A 532 nm green laser which is the second harmonic of the 064 nm laser is oscillated. Then, the plane-parallel substrates 7 and 8
By adjusting the substrate angle of each of the above and adjusting the mode to the gain, an oscillation spectrum as shown in FIG. 5 is obtained.

As a result, it is possible to obtain a green laser light with little high frequency noise and small output fluctuation.

Next, an embodiment of the blue laser will be described with reference to FIG. FIG. 6 shows an embodiment of a wavelength conversion laser device for oscillating a 473 nm blue laser.
The difference from the wavelength conversion laser device that oscillates the green laser is that a Nd: YAG crystal with a width of 1 mm is used as the solid-state laser medium 14 and a K is used as the nonlinear optical crystal 5.
The point is that the NbO ³ crystal is used and the point that the parallel plane substrate 7 having a thickness of 1 mm is removed.

In this wavelength conversion laser device, similarly to the wavelength conversion laser device of FIG. 1, the laser light emitted from the semiconductor laser 1 is collimated by the collimator lens 2 and then converged by the focusing lens 3 to have a width of 1 m.
The solid-state laser medium 4 of m is excited to cause laser oscillation in the Fabry-Perot resonator. At this time, the second harmonic is generated in the nonlinear optical crystal 5 similarly arranged in the resonator, and the 473 nm blue laser which is the second harmonic of the Nd: YAG946 nm laser is oscillated. As a result, wavelength conversion (shortening of the wavelength) is performed, and the short-wavelength laser light passes through the output mirror 6 and is output to the outside of the laser device.

At this time, in the state where the parallel plane substrate 8 is not inserted, this blue laser shows a spectrum as shown in FIG. 7, but the parallel plane substrate 8 is inserted into the resonator and the angle is adjusted to oscillate the oscillation line. When the number is one, a spectrum as shown in FIG. 8 is obtained. At this time, the power is about 30m
Although it decreased to W, the peak value at the specific frequency is about double.

In the case of this blue laser, there is one parallel plane substrate, but since this uses a Nd: YAG crystal as a laser medium having a thickness of 1 mm, this plays the same role as a 1 mm thick substrate. Therefore, it is possible to obtain the same result as that of the green laser. As the green laser, a Nd: YAG crystal having a thickness of 10 mm is used, but if this is made thin, the power is drastically reduced, and therefore the same principle as that of the blue laser cannot be used. The blue laser has an Nd: YAG crystal thickness of 1 mm
Even things that oscillate sufficiently and light is absorbed when they are long, so there is a high possibility that their power will be reduced.

Although the synthetic quarts plate without coating was used as the etalon in the above-mentioned embodiment, it is composed of two partially transmitting mirrors parallel to each other, and both end faces of one plate are highly accurately parallel. It is also possible to use an etalon which has a partially transparent coating on both sides. However, the use of a synthetic quartz plate without coating does not cause a loss of laser power due to the high absorption and reflectance of the coating, so a single longitudinal mode can be achieved with a small loss of power. Since the work of can be omitted, it is very advantageous in terms of cost.

Further, although Nd: YAG crystal is used as the solid-state laser medium in the above-mentioned embodiment, the fundamental wave of several hundred nm to several μm can be selected by selecting other crystal. Further, in the above embodiment, KTP crystal and KNbO ₃ were used as the nonlinear optical crystal to be the SHG element.
Other crystals such as crystals may be used.

In the above embodiment, 0.5 mm and 1.0
Although a parallel plane substrate having a thickness of 0.5 mm, a parallel plane substrate having a thickness of 0.5 mm, and an Nd.YAG crystal having a thickness of 1.0 mm were used, combinations of other thicknesses such as 0.8 to 1.6 mm and 0. The same effect can be obtained by a combination within the range of 4 to 0.8 mm.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made within the scope of the gist of the present invention described in the claims. Is possible. Modified embodiments of the present invention are exemplified below.

(1) In a wavelength conversion type green laser device constructed by using a Fabry-Perot resonator in which a solid-state laser medium and a nonlinear optical crystal are arranged, a plurality of etalons having different widths are arranged in the resonator. A wavelength conversion type green laser device.

(2) In a wavelength conversion type blue laser device constituted by using a Fabry-Perot resonator in which a solid-state laser medium and a nonlinear optical crystal are arranged, a thin solid-state laser medium is used and the solid-state laser is used. A wavelength conversion type blue laser device in which an etalon thinner than the thickness of a medium is arranged in a resonator.

(3) In a wavelength conversion laser device constructed by using a Fabry-Perot resonator in which a solid-state laser medium and a nonlinear optical crystal are arranged, a parallel-plane substrate in which a plurality of coatings having different widths are not applied in the resonator. A wavelength conversion laser device characterized in that

[0031]

The wavelength conversion laser device of the present invention is configured as described above, and since the generation of the longitudinal mode and the generation of the side peak are suppressed by the two etalons having different thicknesses, the output light intensity is increased. Is stable, and a laser with low noise output can be obtained. Further, since the spectrum is a single mode, it becomes a narrow band laser, which is very effective for laser application measurement, optical information recording / reproduction, and the like.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a wavelength conversion laser device of the present invention.

FIG. 2 is a diagram showing an oscillation spectrum line of a wavelength conversion laser device.

FIG. 3 is a diagram showing a transmission curve of a 0.5 mm thick substrate.

FIG. 4 is a diagram showing a transmission curve of a 1 mm thick substrate.

FIG. 5 is a diagram showing an oscillation spectrum line of a wavelength conversion laser device.

FIG. 6 is a diagram showing another embodiment of the wavelength conversion laser device of the present invention.

FIG. 7 is a diagram showing an oscillation spectrum line of the wavelength conversion laser device.

FIG. 8 is a diagram showing an oscillation spectrum line of the wavelength conversion laser device.

FIG. 9 is a diagram showing a conventional wavelength conversion laser device.

FIG. 10 is a diagram showing an oscillation spectrum line of a wavelength conversion laser device.

FIG. 11 is a diagram showing a configuration of an etalon.

FIG. 12 is a diagram showing an oscillation spectrum line of a wavelength conversion laser device.

[Description of Reference Signs] 1 semiconductor laser 2 collimator lens 3 focusing lens 4 solid-state laser medium 5 nonlinear optical crystal 6 output mirror 7 parallel plane substrate 8 parallel plane substrate

Claims (1)

[Claims] 1. A wavelength conversion laser device comprising a Fabry-Perot resonator in which a solid-state laser medium and a nonlinear optical crystal are arranged, wherein a plurality of etalons having different widths are arranged in the resonator. Wavelength conversion laser device.