JP3005405B2 - Up-conversion solid-state laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency up-conversion solid-state laser device capable of emitting blue and green light. Alternatively, the present invention relates to a wavelength conversion solid-state laser device capable of emitting blue and green light.

[0002]

2. Description of the Related Art In recent years, there has been a strong demand for higher densities of optical disks and the like, and accordingly, development of shorter wavelength solid-state lasers has been promoted. Proposals and research and development of short-wavelength (blue and green) laser devices using various methods have been made very actively. Until now, laser oscillation devices using solid-state laser media having a self-harmonic conversion function of semiconductor laser pumping have been developed. There is a report of a laser device that generates a sum frequency using a combination of a semiconductor laser-excited solid-state laser nonlinear optical crystal (Japanese Patent Application No. 4-296072).

On the other hand, as a new type of solid-state short-wavelength laser, a frequency up-conversion laser (up-conversion laser) device has been proposed, and 500 nm by Ho ^{3 +} ions and Pr ^{3 +} ions mixed in glass or fluoride crystals.
Report on Band-Laser Oscillator (Applied Physics Vol. 61, p.
43 1992).

[0004] A laser using YVO ₄ as a laser base material is generally a 1.06 μm laser using an Nd activator.
Other examples of Tm activator lasers (Optics Letters, vol. 17)
189 (1992).

On the other hand, a laser base material of a laser using an Er activator includes glass (reported in Japanese Patent Application No. 61-226297), YLiF ₄ (Electronic Letters (El.
electronics Letters) vol. 25
P1389 1989 _{years), Y 3 Al 5 O 1} 2 and Y ₃ S
c ₂ Ga ₃ O ₁₂ (Journal of Applied Physics (J. of Applied Physics)
s) vol. 70 p7227 1991).

The inventors have succeeded in producing a single crystal composition in which impurity Er is added to YVO ₄ (Japanese Patent Application No. 4-268).
No. 891) and YVO ₄ as a laser base material,
Using Er as an activator, 520-560 nm, 840
A solid-state laser oscillation device which oscillates at 870 nm and 970 to 1020 nm has been proposed (Japanese Patent Application No. 5-7125). This uses the energy transition of the Er ^{3 +} ion, which is the activator, as the energy transition, and a high-efficiency short-wavelength solid-state laser can be obtained.

[0007]

However, the short-wavelength solid-state lasers conventionally developed have the following problems. That is, a solid-state device having a self-harmonic conversion function has a small nonlinear optical constant, and a short-wavelength laser using a sum frequency generation has a complicated optical path. In addition, the above-mentioned frequency up-conversion laser has a problem that the base material is glass or fluoride crystal, and both are difficult to manufacture.

The present invention relates to a YV suitable for pumping a semiconductor laser.
It is an object of the present invention to provide a frequency up-conversion solid-state laser device that can perform high-efficiency and short-wavelength oscillation using an O ₄ crystal.

[0009]

Means for Solving the Problems The inventors have found that Er: YV
In an O ₄ single crystal, multi-step absorption of Er ^{3 +} ions occurs due to excitation of an 800 nm band oscillation semiconductor laser, and the energy is transferred to (VO ₄ ) ^{3 −} , and (VO)
₄ ) It has been found that an Er: YVO ₄ laser oscillation device of frequency up-conversion utilizing ^3-- energy transition can be obtained. Here, when a semiconductor laser having an oscillation wavelength of 809 nm was irradiated to the Er: YVO ₄ single crystal chip,
Green light was observed from the YVO ₄ chips. Observation of this light emission with a spectroscope and a photomultiplier tube revealed that the light emission was around 440 to 515 nm as shown in FIGS. Since Er: YVO ₄ is a uniaxial crystal, its spectral characteristics vary depending on the direction of the crystal axis. In the figure, the σ-polarized light means that the electric field component E of the incident light and the a-axis of the crystal are parallel (E‖a), and the π-polarized light means that the electric field component E of the incident light and the c-axis of the crystal are parallel. Parallel (E‖c). From this emission characteristic, it can be seen that frequency up-conversion in which incident light is converted into a wavelength having a higher frequency than the incident light occurs due to multistage excitation light absorption.

It has been found that this emission wavelength range changes depending on the oscillation wavelength of the semiconductor laser. FIG. 3 shows that the oscillation wavelength of the semiconductor laser is approximately 803, 805, 806,
The emission of Er: YVO ₄ at 807, 809, and 810 nm is shown. The oscillation wavelength of the semiconductor laser changes depending on the temperature and the refractive index. If the principle of the 1.3 μm-band tunable semiconductor laser is applied, the above-mentioned 800 nm-band semiconductor laser is 745-8 nm.
It is tunable at 60 nm. With this oscillation wavelength, E
The light emission of r: YVO ₄ is also variable in wavelength from 400 to 515 nm.

FIG. 4 shows (VO ₄ ) in the Er: YVO ₄ crystal.
The energy level diagrams of ^{3 −} and Er ^{3 +} are shown. The energy transition was found to occur as follows. ^{_{4 I 1 5/2 → 4}} I 9/2 ( excitation by incident ^{_{light) 4 I 9/2 → 4}} I 1 1/2 ( non-radiative _{^{transitions) 4 I 1 1/2 →}} 4 F 3/2 ( excited state This energy is transferred to (VO ₄ ) ^3- ,
A laser beam of 400 to 515 nm is oscillated.

As a result, Er: YVO ₄ becomes a laser medium by a combination of an excitation medium and a resonator, and has a wavelength of 400 nm.
Laser oscillation is possible in a short wavelength region from 515 nm to 515 nm. Here, the resonator is a Fabry-Perot interferometer in which two reflecting mirrors, that is, a high-reflecting mirror having a high reflectance and an output mirror are combined, and the same operation can be obtained even with a mirror coat corresponding to a target wavelength. Also, this resonator has a (VO
₄ ) Energy transition of ^3- ion is available and E
The energy transition of the r ^{3 +} ion is designed to be unavailable.

[0013]

【Example】

(Embodiment 1) FIG. 5 shows an example of a laser oscillation device according to the present invention. A semiconductor laser 1 oscillating in the 800 nm band is used as an excitation light source related to laser oscillation.
r: Irradiate the YVO ₄ laser chip 3. Here, the optical axis of the semiconductor laser and the crystal axis of the Er: YVO ₄ laser chip are arranged so as to have a positional relationship of σ polarization and π polarization. Er: YVO ₄ laser chip, the high reflection mirror coating 4 and the non-reflective coating 5 corresponding to the oscillation wavelength capable band 440 to 500 nm, the antireflection coating 6 corresponding to the oscillation wavelength 800nm band of the semiconductor laser of the pumping light applied And
A resonator structure is taken together with the output coupling mirror 7. In order to collimate the output laser light, a concave lens is used for the output coupling mirror. Embodiment 2 FIG. 6 shows an example of a laser oscillation device according to the present invention. An 800 nm band semiconductor laser 1 whose wavelength is variable depending on temperature and refractive index is used as an excitation light source related to laser oscillation, and the Er: YVO ₄ laser chip 3 is irradiated with excitation light by a condenser lens 2. Here, the optical axis of the semiconductor laser and Er: YVO
_{(4) The} laser chip is arranged so as to have a positional relationship of σ polarized light and π polarized light with the crystal axis of the laser chip. The Er: YVO ₄ laser chip is provided with a high-reflection mirror coat 4 and a non-reflection coat 5 corresponding to a wavelength variable range of 440 to 515 nm, and a non-reflection coat 6 corresponding to an oscillation wavelength of a semiconductor laser of excitation light. A resonator structure is taken together with the coupling mirror 7. In order to collimate the output laser light, a concave lens is used for the output coupling mirror. The oscillation wavelength of the semiconductor laser is controlled by the temperature controller 8. FIG. 7 shows an example of the correlation between the temperature controller and the semiconductor laser oscillation wavelength.

In the solid-state laser device according to the first embodiment,
At an excitation wavelength of 809 nm, green laser oscillation of 482 nm was confirmed. In the laser device according to the second embodiment,
Green laser 400-51 at excitation wavelength 745-860 nm
5 nm was confirmed.

[0015]

The up-converting solid-state laser device according to the present invention has the advantages of both a semiconductor laser and a solid-state laser, is a compact laser device with simple alignment, and can be used in place of a gas argon laser. Also,
The oscillation wavelength of this laser device can be expected to be applied in the fields of optical disk read / write, laser printer, and scientific measurement.

[Brief description of the drawings]

FIG. 1: Er for σ-polarized light at 400-515 nm:
FIG. 3 is a view showing the light emission characteristics of a YVO ₄ crystal.

FIG. 2 Er at π polarization from 400 to 515 nm:
FIG. 3 is a view showing the light emission characteristics of a YVO ₄ crystal.

FIG. 3 Er at 400-515 nm with σ polarization:
FIG. 3 is a view showing the light emission characteristics of a YVO ₄ crystal.

FIG. 4 is an energy level diagram in an Er: YVO ₄ crystal.

FIG. 5 is a diagram of a laser oscillation device according to the first embodiment of the present invention.

FIG. 6 is a diagram of a laser oscillation device according to a second embodiment of the present invention.

FIG. 7 is a diagram illustrating a relationship between a temperature controller and an oscillation wavelength of a semiconductor laser according to a second embodiment.

FIG. 8 is a diagram showing a relationship between an oscillation wavelength of a semiconductor laser and a laser wavelength emitted from Er: YVO ₄ in Example 2.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 semiconductor laser 2 condenser lens 3 Er: YVO ₄ 4 TiO ₂ / SiO ₂ high reflection mirror coat for target wavelength 5 magnesium fluoride / zeolite anti-reflection coat corresponding to target wavelength 6 corresponding to oscillation wavelength of semiconductor laser Magnesium fluoride / zeolite anti-reflection coating 7 Output coupling mirror 8 Temperature controller

Continuing from the front page (72) Inventor Kenta Naito 29-15, Arisato-cho, Ikoma, Nara Prefecture (72) Inventor Shoko Mako 5-7-1 Shiba, Minato-ku, Tokyo NEC Corporation (72) Inventor Seiichi Saito, 5-7-1 Shiba, Minato-ku, Tokyo NEC Corporation (72) Inventor Yasuhiko Kuwano 7-1-1 Shiba, Minato-ku, Tokyo NEC Corporation (58) Field surveyed (Int. Cl. ^7, DB name) H01S 3/10 G02F 1/35 505 H01S 3/0941 H01S 3/16

Claims (2)

(57) [Claims] 1. A single crystal composition Er: YVO _{4 obtained} by mixing impurities Er into a composition represented by a composition formula YVO ₄ ,
By irradiating a 0 nm band semiconductor laser ,
Multi-step within multiple energy levels with Er ³⁺ ions
Absorption occurs, and the energy of (VO ₄ ) in the crystal
Transition to the energy level formed by ^3- ions and relax
An up-conversion solid-state laser device that uses sum emission . 2. The frequency up-conversion solid-state laser device according to claim 1, wherein a variable oscillation wavelength is obtained in a wavelength range from 400 nm to 515 nm in response to the conversion of the oscillation wavelength of the semiconductor laser as an excitation light source.