JPH06283786A - Laser diode pumped solid laser - Google Patents

Abstract

PURPOSE:To suppress the noise generation of wavelength-converted wave due to returning lights to a semiconductor laser and efficiently provide a stable continuous wavelength-converted wave by providing a laser diode pumped solid laser, which pumps the solid laser medium to which rare earth materials such as neodymium is added by using the semiconductor laser and converts the wavelength of the solid laser beam by non-linear optical material crystal arranged in the resonator. CONSTITUTION:A vertical/horizontal single mode semiconductor laser 11 is used as a semiconductor laser, and high-frequency current RF with shorter cycle than the fluorescence life of YAG crystal 13, which is the solid laser medium, is superimposed on the driving current I of the semiconductor laser 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser diode pumped solid-state laser, and more specifically, a crystal of a non-linear optical material is arranged in a resonator for wavelength conversion (shortening of wavelength) of a solid-state laser beam. Laser diode pumping solid-state laser.

[0002]

2. Description of the Related Art A laser diode pumping solid-state laser for pumping a solid-state laser medium doped with a rare earth element such as neodymium with a semiconductor laser (laser diode) is known as disclosed in, for example, Japanese Patent Application Laid-Open No. 62-189783. ing. In this type of laser diode pumped solid state laser, for example
As shown in Japanese Patent Publication No. 2-77181, in order to obtain a laser beam having a shorter wavelength, a bulk single crystal of a nonlinear optical material for wavelength-converting a solid-state laser beam is arranged in the resonator to obtain a solid-state laser. Wavelength conversion of the beam into a second harmonic wave or the like is also performed.

[0003]

By the way, when a vertical / horizontal single-mode semiconductor laser is used as a semiconductor laser as a pumping source of the laser diode pumping solid-state laser as described above, this semiconductor laser has an influence of return light. It often causes mode hopping. When this mode hopping occurs, noise is generated in the solid-state laser beam, and as a result, noise is also generated in the wavelength converted wave.

On the other hand, since a vertical / horizontal multimode semiconductor laser such as a broad area laser or a phased array laser is not easily affected by the returning light, if such a semiconductor laser is used as a pumping source, the above mode hopping is performed. It is possible to suppress noise generation due to. However, in that case, since the emission width of the semiconductor laser is relatively wide, for example, about 50 μm, the laser beam emitted from the semiconductor laser and incident on the solid-state laser medium cannot be sufficiently narrowed, which causes a decrease in efficiency. It was connected. Further, in particular, in the broad area laser, the transverse mode changes depending on the drive current value and the temperature, so that the excitation state of the solid-state laser medium fluctuates, which causes fluctuations in the output of the wavelength-converted wave.

As a measure for returning light, other than laser diode pumping solid-state lasers that perform wavelength conversion, as disclosed in, for example, Japanese Unexamined Patent Publication No. 2-203324,
There is known a method of driving a semiconductor laser of a vertical single mode by superposing a high frequency. However, when the semiconductor laser is driven by high frequency superposition, the output of the wavelength-converted wave obtained in many cases becomes a pulse because the longitudinal mode flies.

The present invention has been made in view of the above circumstances, and it is possible to suppress the generation of noise in the wavelength-converted wave due to the return light to the semiconductor laser and to efficiently obtain a stable wavelength-converted wave with continuous output. The object is to provide a laser diode pumped solid state laser.

[0007]

A laser diode pumped solid-state laser according to the present invention is obtained by pumping a solid-state laser medium doped with a rare earth element such as neodymium with a semiconductor laser as described above and resonating the obtained solid-state laser beam. In the laser diode pumped solid-state laser that performs wavelength conversion by the crystal of the nonlinear optical material arranged in the chamber, a vertical / horizontal single-mode semiconductor laser is used as the semiconductor laser. It is characterized in that a high frequency having a shorter cycle is superimposed.

[0008]

[Operation and effect of the invention]
Since the lateral single mode semiconductor laser is driven by high frequency superposition, its longitudinal mode becomes multimode, mode hopping of the semiconductor laser due to returning light is suppressed, and a wavelength-converted wave without noise can be obtained.

In this case, the period of the high frequency to be superimposed on the driving current of the semiconductor laser is set shorter than the fluorescence lifetime of the solid laser medium. The response of the laser medium cannot follow and the solid-state laser has continuous output. As a result, the wavelength converted wave also becomes a continuous output.

Since the lateral single-mode semiconductor laser used in the above structure has an extremely narrow emission width as compared with the lateral multi-mode semiconductor laser, the laser beam emitted from the semiconductor laser is sufficiently narrowed to be a solid-state laser. It can be made incident on the medium. As a result, a high-power solid-state laser beam can be generated with high efficiency, and a high-power wavelength-converted wave can be obtained.

Further, when the lateral single mode semiconductor laser is used as described above, the excited state of the solid-state laser medium does not change due to the change of the lateral mode as in the case of using the lateral multimode semiconductor laser. Therefore, the output of the wavelength converted wave is stabilized.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on the embodiments shown in the drawings. FIG. 1 shows a laser diode pumped solid state laser according to a first embodiment of the present invention. This laser diode pumped solid-state laser includes a semiconductor laser 11 that emits a laser beam 10 as pumping light and the laser beam 10 that is divergent light.
Lens that consists of a gradient index lens that focuses light
12, a YAG crystal 13 which is a solid-state laser medium doped with neodymium (Nd), a resonator mirror 14 arranged on the front side (right side in the drawing) of the YAG crystal 13, and this resonator mirror 14. Between the YAG crystal 13 and the KNb
It consists of O ₃ (KN) crystal 15. Each element described above is
It is mounted and integrated in a common housing (not shown). The semiconductor laser 11 is temperature-controlled to a predetermined temperature by a Peltier device and a temperature-adjusting circuit (not shown).

As the semiconductor laser 11, a vertical / horizontal single mode laser emitting a laser beam 10 having a reference wavelength λ ₁ = 808 nm is used. On the other hand, YAG crystal 13
Is cut into a diameter of 3 mm and a thickness of 1 mm, and a wavelength λ ₂ =
It emits a laser beam 16 of 946 nm. Also KN crystal 15
Is cut into a length and width of 3 × 3 mm and a thickness of 1 mm.

The light passing end faces 13a and 13b of the YAG crystal 13, the light passing end faces 15a and 15b of the KN crystal 15, and the mirror surface 14a of the resonator mirror 14 formed to be a part of the spherical surface are respectively provided with the above wavelength λ. ₁ = 808 nm, wavelength λ ₂ = 946 n
m and light having a wavelength λ ₃ = 473 nm described later are coated with the following characteristics. AR is non-reflective (transmittance 99% or more), HR is highly reflective (reflectance 99.9).
% Or more).

808 nm 946 nm 473 nm End face 13a AR HR-End face 13b-AR HR End face 15a-AR AR End face 15b-AR AR Mirror face 14a-HR AR Laser beam 16 with wavelength λ ₂ = 946 nm 16 Is
It is confined between the above-mentioned surfaces 13a and 14a and causes laser oscillation. The laser beam 16 is incident on the KN crystal 15 which is a nonlinear optical material, a wavelength _{λ 3 = λ 2/2 =} 47
The wavelength is converted to the second harmonic wave 17 of 3 nm. Resonator mirror
Since the mirror surface 14a of 14 is coated as described above, the mirror surface 14a of
Only harmonics 17 are extracted.

Here, the driving current I of the semiconductor laser 11 generated by the driver 18 is superposed with the high frequency current RF generated by the high frequency oscillator 19. The frequency of the high frequency current RF is 650 MHz, for example. In this way, when the vertical single mode semiconductor laser 11 is driven by high frequency superposition,
The longitudinal mode becomes the multimode as shown in FIG. 2, the mode hopping of the semiconductor laser 11 due to the returning light is suppressed, and the noise-free second harmonic 17 can be obtained.
This laser diode pumped solid-state laser was used in the operating temperature range of 10 ℃ to specifically investigate the noise generation situation.
An environmental test was conducted at 40 ° C. and a temperature gradient of 60 ° C./h, but no noise was generated in the second harmonic wave 17.

In this case, the fluorescence lifetime τ of the YAG crystal 13 is 250 μs, and the period 1.54 ns of the high frequency current RF having a frequency of 650 MHz is smaller than that by five digits or more. With this, the semiconductor laser by high frequency superposition
The response of the YAG crystal 13 cannot follow the change in the longitudinal mode of 11, and the solid-state laser has a continuous output. If so, the second harmonic 17 also becomes a continuous output.

Further, the emission width of the lateral single mode semiconductor laser 11 is sufficiently narrow as 3 μm, and in the above-mentioned structure using it, the laser beam 10 is focused by the condenser lens 12.
After condensing to a spot diameter of 3 μm with a YAG crystal
It can be incident on 13. In this way, if the laser beam 10 is sufficiently narrowed and made incident on the YAG crystal 13,
A high-power solid-state laser beam 16 can be generated with high efficiency, and a high-power second harmonic wave 17 can be obtained. In this embodiment, when the output of the semiconductor laser 11 was 100 mW, the second harmonic wave 17 of 2 mW was obtained.

When the lateral single mode semiconductor laser 11 is used as described above, the excited state of the YAG crystal 13 may change due to the change of the lateral mode as in the case of using the lateral multimode semiconductor laser. The output of the second harmonic 17 is thus stabilized.

Next, a comparative example for confirming the effect of the present invention will be described. First, as Comparative Example 1, a vertical / horizontal single mode semiconductor laser 11 of the device of the first embodiment is used.
Was replaced with a broad area laser with an emission width of 50 μm. In the device of Comparative Example 1, even if the laser beam as the pumping light emitted from the broad area laser is focused by the focusing lens 12, the spot diameter is 50
It can only be limited to μm. Therefore, the output of the solid-state laser beam is lower than that in the first embodiment, and eventually the output of the second harmonic wave is reduced. Specifically, when the output of the broad area laser is 100 mW, the second harmonic output is 0.4 mW, which is ⅕ of the second harmonic output of the first embodiment.

As Comparative Example 2, the semiconductor laser 11 of the device of the first embodiment was driven without high frequency superposition.
In that case, the semiconductor laser 11 operates in the original vertical single mode, so the laser beam emitted from it
The absorption efficiency of the YAG crystal 13 of 10 is improved, and the output of the semiconductor laser 11 is 100 mW.
Harmonics 17 are obtained. However, when the laser diode pumped solid-state laser of Comparative Example 2 is subjected to the above-described environmental test, mode hopping occurs in the semiconductor laser 11 due to the return light from the YAG crystal 13 and noise is generated in the second harmonic wave 17. .

Next, a second embodiment of the present invention will be described with reference to FIG. In FIG. 3, the same elements as those in FIG. 1 are designated by the same reference numerals, and the duplicated description thereof will be omitted. In the laser diode pumped solid-state laser of the second embodiment, a vertical / horizontal single mode semiconductor laser 11 that emits a laser beam 10 as pumping light is fixedly held on a mount 30. The YAG crystal 13 has an end face 13a on the light incident side fixed to the mount 30, and a semiconductor laser is attached to the end face 13a.
11 is fixed directly. And KN crystal 15 is YAG
It is closely fixed to the crystal 13. The mount 30 is fixed on a Peltier element 31, and the semiconductor laser 11, the YAG crystal 13 and the KN crystal 15 are temperature-controlled to a predetermined temperature by the Peltier element 31 and a temperature control circuit (not shown).

End face 13a of YAG crystal 13 and KN crystal 15
The end surfaces 15b of the respective are coated with the following characteristics with respect to the light having the wavelength λ ₁ = 808 nm, the wavelength λ ₂ = 946 nm and the wavelength λ ₃ = 473 nm. AR indicates no reflection (transmittance 99% or more), and HR indicates high reflection (reflectance 99.9% or more).

808 nm 946 nm 473 nm End face 13a AR HR− End face 15b−HR AR Therefore, the laser beam 16 with wavelength λ ₂ = 946 nm is
It is trapped between the surfaces 13a and 15b and causes laser oscillation. That is, in this case, the YAG crystal end face 13a
The KN crystal end face 15b constitutes a solid-state laser resonator. This laser beam 16 enters a KN crystal 15 which is a non-linear optical material and has a wavelength of λ ₃ = 473 nm.
The wavelength is converted into the second harmonic wave 17 of. Since the KN crystal end face 15b is coated as described above, almost only the second harmonic wave 17 is extracted from this KN crystal 15.

Also in this embodiment, the driving current I of the semiconductor laser 11 generated by the driver 18 is superposed with the high frequency current RF of 650 MHz generated by the high frequency oscillator 19. By driving the semiconductor laser 11 of the longitudinal single mode in a high frequency superposition manner in this way, the noise generation of the second harmonic 17 is prevented and the second harmonic is continuously output in this embodiment as in the first embodiment. And the effect is obtained. Further, since the semiconductor laser 11 of the lateral single mode is used, the second harmonic wave 17 of high output can be obtained and the output thereof can be stabilized similarly to the first embodiment. The effect is obtained.

If the period of the high frequency wave superposed on the driving current of the semiconductor laser is shorter than the fluorescence life of the solid laser medium, the effect of continuously outputting the wavelength-converted wave can be obtained. If it is set to 1/10 or less, good results can be obtained.

[Brief description of drawings]

FIG. 1 is a side view of a first embodiment device of the present invention.

FIG. 2 is a graph showing an emission spectrum of a semiconductor laser in the device of the first embodiment.

FIG. 3 is a side view of a second embodiment device of the present invention.

[Explanation of symbols]

 10 Laser beam (pumping light) 11 Semiconductor laser 12 Condenser lens 13 YAG crystal 14 Resonator mirror 15 KN crystal 16 Laser beam (fundamental wave) 17 Second harmonic 18 Semiconductor laser driver 19 High-frequency oscillator 30 Mount 31 Peltier device

Claims (1)

[Claims] 1. A semiconductor laser pumping a solid-state laser medium to which a rare earth element such as neodymium is added,
A laser diode pumped solid-state laser in which the obtained solid-state laser beam is wavelength-converted by a crystal of a nonlinear optical material arranged in a resonator, wherein a vertical / horizontal single-mode laser is used as the semiconductor laser. A laser diode pumped solid-state laser, characterized in that a high frequency having a period shorter than the fluorescence lifetime of the solid-state laser medium is superimposed on the electric current.