JP2908681B2 - Upconversion laser material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in the field of optical memory, optical measurement, and optical information processing using laser light, particularly visible laser light, and is capable of obtaining laser light having a wavelength shorter than the excitation wavelength. Related to up-conversion laser materials.

[0002]

_2. Description of the Related Art Heretofore, as an up-conversion laser, an Er ³⁺ / Yb ³⁺ : BaY ₂ F ₈ crystal has been used, and a green (550 n) at a temperature of 77 K is excited by a xenon lamp.
m) laser oscillation [L. F. Johnso
n, et al. , Appl. Phys. Lett. 1
9, 44 (1971)], an example in which green (550 nm) laser oscillation was obtained at a temperature of 77 K using Er ³⁺ : YAlO ₃ crystal [A. J. Silversmith, et
al. , Appl. Phys. Lett. 51,19
77 (1987)], using Er ³⁺ : LiYF ₄ crystal,
Green (551n) at a temperature of 40K by semiconductor laser excitation
m) laser oscillation example [F. Tong, et
al. , Electron. Lett. 25,1389
(1989)], using an Nd ³⁺ : LaF ₃ crystal, and using a semiconductor laser as an excitation light source at a temperature of 90 K or less and an ultraviolet (3
80 nm) laser oscillation [R. M. Ma
cfarlane et al. , Appl. Phys
s. Lett. 52, 1300 (1988)]. However, when these bulk crystal laser active media are used, there is a problem that upconversion laser oscillation cannot be obtained unless the temperature is much lower than room temperature. . In addition, in the case of an up-conversion laser material, it is necessary to avoid the influence of concentration quenching due to the interaction between rare earth element ions. Since rare earth element ions cannot be added at a high concentration, the excitation light must be absorbed efficiently. There is a restriction that the irradiation region needs a uniform crystal of at least several cm.

[0003]

SUMMARY OF THE INVENTION The present invention is to provide an up-conversion laser material having a fine spherical shape so that a small crystal can efficiently absorb excitation light and efficiently confine up-conversion emission in the laser material. It is another object of the present invention to provide a minute up-conversion laser material in which an up-conversion laser oscillates near room temperature.

[0004]

According to the present invention, an up-conversion laser crystal containing at least one of erbium, holmium, praseodymium, thulium, neodymium and cerium as rare earth element ions is formed into a fine spherical shape by polishing or the like. It is achieved by doing.

When the microsphere crystal is irradiated with laser light oscillated with light energy in the light absorption region of rare earth element ions as active ions, the rare earth element ions are changed from the first energy level to the first energy level. When excited to a higher second energy level and from the second energy level or from a third energy level lower than the second energy level and higher than the first energy level, FIG.
Due to the energy transfer between the excited ions as shown in (a) or the excited state absorption (multi-step excitation) as shown in FIG. 1B, the energy is further shifted to the fourth energy level higher than the second energy level. Being excited to emit light from the fourth energy level or a fifth energy level lower than the fourth energy level and higher than the second energy level to the first energy level, The so-called up-conversion emission, which emits light having a wavelength shorter than the wavelength of the incident light, occurs inside the microsphere, and the up-conversion emission enters the interface between the inside and the outside of the microsphere at an angle larger than the critical angle. Light repeats total reflection at the interface. When the light that repeats the total reflection and rotates in the microsphere has the same phase, the light resonates, and the microsphere itself functions as a resonator, and the fourth energy level or the fifth energy level is used. By causing an inversion distribution between the first energy level and the fourth energy level.
Energy level or the fifth energy level and the first energy level
Oscillates a laser beam having a wavelength corresponding to the energy difference from the energy level.

[0006] In the present invention, the amount of rare earth element ion added is suitably in the range of 50 to 5000 ppm, and more preferably 300 to 1500 ppm. When the amount of the rare earth element ion added is less than 50 ppm, the absorption efficiency of the excitation laser light is poor, and upconversion laser oscillation is unlikely to occur. The rare earth element ion addition amount is 5000
When the concentration is not less than ppm, concentration quenching occurs due to the interaction between rare earth element ions, and upconversion laser oscillation is less likely to occur. In addition, luminous efficiency can be improved by co-adding Yb ³⁺ or the like as a sensitizing ion separately from the rare earth element ion.

[0007] The refractive index of the microsphere crystal is preferably 1.3 or more in the laser oscillation wavelength range, and when it is smaller than 1.3, light cannot be effectively confined, and up-conversion laser oscillation hardly occurs.

[0008] The size of the microsphere crystal is not particularly limited, but in consideration of handling, the size is suitably in the range of 50 to 2000 µm, more preferably 200 to 1000 µm. Since the light leakage due to the diffraction effect becomes relatively smaller as the size of the microsphere increases, the Q of the microsphere resonator increases.
The value increases, and upconversion laser oscillation occurs at a low threshold. However, as the Q value increases, many resonance modes exist, and the spectrum of the oscillation line becomes complicated. It is preferable to determine them together.

The microsphere crystal material is preferably a single crystal of fluoride, a single crystal of chloride, a single crystal of bromide, or a single crystal of iodide. In particular, in consideration of chemical durability and mechanical strength, Ba is preferable.
Fluoride single crystals such as F ₂ , CaF ₂ and LYF ₄ are more preferred. In consideration of the oscillation efficiency, a crystal having a smaller phonon energy is preferable, but a crystal having a material intrinsic absorption at the excitation light wavelength and the up-conversion laser oscillation wavelength is not preferable because the oscillation efficiency is reduced.

[0010]

[Function] By making the up-conversion laser crystal into a micro-sphere shape, confining light, and using the micro-sphere itself as a resonator, it is possible to increase the Q value of the resonator, and it is difficult to obtain a bulk shape. Up-conversion laser light can be easily obtained at room temperature.

[0011]

EXAMPLES Examples of the present invention will be specifically described below, but the present invention is not limited to these examples.

Embodiment FIG. 2 shows an embodiment of an up-conversion microsphere laser according to the present invention, in which 1 is an excitation light source, 2 is an excitation light condensing lens, 3 is a rare earth-doped microsphere, and 4 is an emission from the microsphere. An elliptical reflector for collecting the up-conversion laser light to be collected at one point, a fiber 5 for transmitting the collected laser light, and a lens 6 for collecting the up-conversion laser light from the fiber. The excitation light source is a Ti: sapphire laser, and the rare earth-doped microspheres have a diameter of 500 μm and a diameter of 5 μm.
It is a LiYF ₄ fluoride single crystal to which 00 ppm of Er ³⁺ is added.

[0013] The laser beam of 800nm from the excitation light source 1 is condensed by a lens 2, by irradiating as shown at 7 in Figure 3 to the end of the rare earth-doped microspheres 3, ⁴ of the Er ³⁺ I _15/2
→ ⁴ I _9/2 excitation and ⁴ I _11/2 → ⁴ F by ⁴ F _7/2 excitation
_{That 3/2} → ⁴ I _15/2 laser beam 550nm due to transition was obtained was confirmed from the existence of the oscillation spectrum and thresholds (150 mW).

In this embodiment, LiYF doped with Er ³⁺ is used.
Although using _four fluoride single crystal microspheres, using LiYF ₄ single crystal microspheres added with Tm ^3+, dye laser excitation (65
(0 nm), it was confirmed that a 480 nm laser beam could be obtained.

Further, as a laser medium, a LaF ₃ single crystal,
Up-conversion laser light using BaF ₂ single crystal, NaCl or KBr single crystal and changing the excitation wavelength of each microsphere to which Ho ³⁺ , Pr ³⁺ , Ce ³⁺ or Nd ³⁺ is added as a rare earth element ion. It is possible to obtain

[0016]

As described above, the light confinement effect can be realized by forming the up-conversion laser crystal material into a microsphere shape, and at the same time, the bulk crystal is used by using the microsphere itself as a resonator. Compared with an up-conversion laser, the Q value of the resonator can be increased, and up-conversion laser oscillation at room temperature, which is difficult with a bulk crystal, can be performed.

[Brief description of the drawings]

FIG. 1 shows an up-conversion excitation mechanism. (A) Energy transfer between excited ions (b) Excited state absorption (multi-step excitation)

FIG. 2 is a configuration diagram showing an embodiment of an up-conversion laser using a rare-earth-doped microsphere crystal as an up-conversion laser material.

FIG. 3 shows an example of excitation light irradiation on a rare earth-doped microsphere crystal.

[Explanation of symbols]

 1. Excitation light source 2. 2. Condensing lens 3. Rare earth-doped microsphere crystal Elliptical reflector 5. Optical fiber 6. Condensing lens 7. Focused excitation laser

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Natsumura Nishimura 5253 Oki Ube, Oji, Ube City, Yamaguchi Prefecture Central Glass Co., Ltd.Ube Research Laboratories (72) Inventor Yasushi Yasuda 5253 Oki Ube, Oji Ube City, Yamaguchi Prefecture, Central Ube Laboratory, Glass Co., Ltd. (56) References JP-A-63-177483 (JP, A) JP-A-63-503495 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01S 3/06 H01S 3/16-3/17

Claims (1)

(57) [Claims] 1. A rare earth element ion containing at least one of erbium, holmium, praseodymium, thulium, neodymium and cerium, and having a content of 5
The particle size is in the range of 0 to 5000 ppm, and the particle size is 50 to 200 ppm.
An up-conversion laser material, which is a microsphere crystal having a diameter of 0 μm, and the crystal is a single crystal of fluoride, a single crystal of chloride, a single crystal of bromide, or a single crystal of iodide.