JPH07162063A - Up-conversion laser material - Google Patents

Abstract

PURPOSE:To realize up-conversion laser oscillation at a temperature approximate to a room temperature, by constituting up-conversion laser crystal in the state of microspheres, confining light, and making the microsphere itself work as a resonator. CONSTITUTION:Microspheric crystal is fluoride single crystal, chloride single crystal, bromide single crystal, and iodide single crystal. The grain diameter is in the range of 50-2000mum. The content of rare earth element ions is in the range of 50-5000ppm. From a pumping light source 1, 800nm laser light is converged by using a lens 2, and the end of a rare earth added microsphere 3 is irradiated with the laser light. It was recognized by the existance of oscillation spectrum and a threshold value (150mW) that 550nm laser light is obtained at the result of <4>S3/2 <4>I15/2 transition by the <4>I15/2 <4>I9/12 excitation and <4>I11/2 <4>F7/2 excitation of Er<3+>. Hence the Q value of a resonator can be made large, and up-conversion laser oscillation at a room temperature which is difficult in the case of bulk crystal is enabled.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention is used in the field of optical memory, optical measurement and optical information processing utilizing laser light, particularly visible laser light, and is capable of obtaining laser light having a wavelength shorter than the excitation wavelength. Up conversion laser material.

[0002]

_2. Description of the Related Art Conventionally, an Er ³⁺ / Yb ³⁺ : BaY ₂ F ₈ crystal has been used as an up-conversion laser, and a green (550n
m) laser oscillation was obtained [L. F. Johnso
n, et al. , Appl. Phys. Lett. 1
9, 44 (1971)], using Er ³⁺ : YAlO ₃ crystal, an example in which green (550 nm) laser oscillation was obtained at a temperature of 77 K [A. J. Silversmith, et
al. , Appl. Phys. Lett. 51, 19
77 (1987)], using Er ³⁺ : LiYF ₄ crystal,
Green (551n
m) laser oscillation is obtained [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, ultraviolet (3
Example in which laser oscillation in the 80 nm region was obtained [R. M. Ma
cfarlane et al. , Appl. Phy
s. Lett. 52, 1300 (1988)], etc., but when using these bulk crystal laser active media, up-conversion laser oscillation cannot be obtained unless the temperature is much lower than room temperature. . In addition, in up-conversion laser materials, it is necessary to avoid the effect of concentration quenching due to the interaction between rare earth element ions, and since it is not possible to add rare earth element ions at high concentration, in order to absorb the excitation light efficiently, There is a constraint that the irradiation region needs a uniform crystal of at least several cm or more.

[0003]

DISCLOSURE OF THE INVENTION The present invention aims to efficiently absorb excitation light in a small crystal and confine the up-conversion emission in the laser material by making the up-conversion laser material into a microsphere shape. An object of the present invention is 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 made into a fine spherical shape by polishing or the like. It is achieved by doing.

When the microsphere crystal is irradiated with a laser beam oscillated with the light energy of the light absorption region of the rare earth element ion which is the active ion, the rare earth element ion moves from the first energy level to the first energy level. Excited to a higher second energy level and from the second energy level or a third energy level lower than the second energy level and higher than the first energy level, FIG.
By the energy transfer between excited ions as shown in (a) or the excited state absorption (multi-step excitation) as shown in FIG. 1 (b), a fourth energy level higher than the second energy level is obtained. By being excited and making an emission transition 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 with a wavelength shorter than the wavelength of incident light, occurs inside the microsphere, and of this up-conversion emission, the light enters the boundary between the inside and the outside of the microsphere at an angle larger than the critical angle The light repeats total internal reflection at the boundary surface. 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 generated. Between the first energy level and the fourth energy level
Energy level or fifth energy level and the first
Laser light having a wavelength corresponding to the energy difference from the energy level of

In the present invention, the amount of rare earth element ions added is preferably in the range of 50 to 5000 ppm, 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 hardly occurs. Also, the amount of rare earth element ions added is 5000
When it is at least ppm, concentration quenching occurs due to the interaction between rare earth element ions, and upconversion laser oscillation becomes difficult to occur. It is also possible to improve the luminous efficiency by co-adding Yb ³⁺ or the like as a sensitizing ion in addition to the rare earth element ion.

The refractive index of the microsphere crystal is preferably 1.3 or more in the laser oscillation wavelength range. If it is smaller than 1.3, optical confinement cannot be effectively performed, and up-conversion laser oscillation becomes difficult to occur.

The size of the microsphere crystal is not particularly limited, but in consideration of handling, the range of 50 to 2000 μm is suitable, and more preferably 200 to 1000 μm. As the size of the microsphere becomes larger, the light leakage due to the diffraction effect becomes relatively smaller.
The value becomes large and up-conversion laser oscillation occurs at a low threshold value. However, as the Q value becomes large, 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 fluoride single crystal, a chloride single crystal, a bromide single crystal, or an iodide single crystal, especially Ba in view of chemical durability and mechanical strength.
Fluoride single crystals of F ₂ , CaF ₂ , LYF _{4 and the} like are more preferable. A crystal having a smaller phonon energy is more preferable in consideration of oscillation efficiency, but a crystal having intrinsic absorption of the material at the pumping light wavelength and the up-conversion laser oscillation wavelength is not preferable because the oscillation efficiency is lowered.

[0010]

By making the up-conversion laser crystal into a microsphere shape for optical confinement and using the microsphere itself as a resonator, the Q value of the resonator can be increased, which is difficult to obtain in the 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.

EXAMPLE FIG. 2 shows an example of an up-conversion microsphere laser of 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 a microsphere. An ellipsoidal reflector that collects the up-converted laser light at one point, 5 is a fiber that transmits the collected laser light, and 6 is a lens that collects the up-converted laser light from the fiber. The excitation light source was a Ti: sapphire laser, and the diameter of the rare-earth-doped microspheres was 500 μm.
It is a LiYF ₄ fluoride single crystal added with 00 ppm Er ³⁺ .

[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 _7/2 excitation ⁴ S
It was confirmed from the existence of the oscillation spectrum and the threshold value (150 mW) that the laser light of 550 nm was obtained due to the _3/2 → ⁴ I _15/2 transition.

In this example, LiYF doped with Er ³⁺ is used.
_Although tetrafluoride single crystal microspheres were used, dye laser excitation (65%) was performed using LiYF ₄ single crystal microspheres added with Tm ^3+.
It was also confirmed that 480 nm laser light can be obtained by 0 nm).

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

[0016]

As explained above, the optical confinement effect can be realized by forming the up-conversion laser crystal material into a microsphere shape, and at the same time, by using the microsphere itself as a resonator, a bulk crystal is used. As 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 for a bulk crystal, becomes possible.

[Brief description of drawings]

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

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

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

[Explanation of symbols]

 1. Excitation light source 2. Condensing lens 3. Rare earth added microsphere crystal 4. Elliptical reflector 5. Optical fiber 6. Condensing lens 7. Focused pump laser

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location H01S 3/16 (72) Inventor Natsuya Nishimura 5253 Obu Oki, Ube City, Yamaguchi Prefecture Central Glass Shares Company Ube Laboratory (72) Inventor Yasushi Kida 5253 Oki Ube, Ube City, Yamaguchi Central Glass Co., Ltd. Ube Laboratory

Claims (5)

[Claims] 1. An upconversion laser material, which is a microsphere crystal containing rare earth element ions. 2. The up-conversion laser material according to claim 1, wherein the rare-earth element ion contains at least one of erbium, holmium, praseodymium, thulium, neodymium and cerium. 3. The content of rare earth ion is 50 to 50.
The up-conversion laser material according to claim 1, which is in a range of 00 ppm. 4. The up-conversion laser material according to claim 1, wherein the microsphere crystal is a fluoride single crystal, a chloride single crystal, a bromide single crystal, or an iodide single crystal. 5. The particle size of the microsphere crystal is 50 to 2000 μm.
The up-conversion laser material according to claim 1, wherein