JPH0779046A - Niobic acid lithium single crystal and laser oscillator using that single crystal - Google Patents

Abstract

PURPOSE:To provide a small and simple laser oscillator, which can oscillate a green laser beam, and a single crystal used as a laser medium by using a niobic acid lithium single crystal, which contains specified quantities of neodymium and scandium, as the laser medium of a solid laser oscillator. CONSTITUTION:A niobic acid lithium single crystal, which contains 0.01-0.5wt.% neodymium ions and 0.05-0.5wt.% scandium ions, is used as a laser medium. A sapphire laser doped with titanium ions or a semiconductor laser is used as an exciting light source of 813nm. This laser beam is condensed with a lens 2, and is led in a laser medium 4 (niobic acid lithium single crystal), passing through a mirror 3 The laser medium 4 absorbs the laser beam of 813nm with neodymium ions, and oscillates a laser beam of 1092nm, and at the same time, oscillates also with green of 546nm being the second higher harmonics of the laser beam of 1092nm by the nonlinear effect that the single crystal has.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium niobate single crystal (LiNbO ₃ ) and a laser oscillator using the single crystal as a laser medium. In particular, it contains a certain amount of neodymium (Nd) ions and scandium (Sc) ions simultaneously. The present invention relates to a lithium niobate single crystal and a laser oscillator that oscillates a green laser beam using the single crystal.

[0002]

2. Description of the Related Art In recent years, with the progress of optical memory technology, demands for shortening the wavelength of a light source for improving the writing density and downsizing the entire device have become strict. Currently, the reading light sources for compact discs, etc. are from the first generation using a semiconductor laser that oscillates in the near infrared region to neodymium (N
d) It is changing to the second generation that uses green light obtained by wavelength-doubling a laser.

In this second generation system, the base material of neodymium is Y ₃ Al ₅ O ₁₂ (YAG), YLiF ₄ (YLF),
YVO ₄ (YVO) and the like, and potassium titanium phosphate (KTP: KTiOPO) is used as a nonlinear crystal for wavelength doubling.
₄ ), lithium niobate, etc. are mainly used.

However, potassium titanate requires angular phase matching for wavelength doubling, and requires special attention during assembly of the device for high efficiency. on the other hand,
Although 90 ° phase matching is possible with lithium niobate, this crystal originally tends to cause a change in the refractive index due to light (optical damage), and magnesium oxide has been added to reduce this. As a result, the phase matching temperature is 1
Since the temperature is as high as about 50 ° C., two independent temperature control systems are required together with those for semiconductor lasers, which is an obstacle to miniaturization.

As one of the attempts to miniaturize the light source element, there is a method in which the laser medium itself has nonlinearity and oscillation and multiplication are performed in the same crystal. This phenomenon is 196
It was confirmed that the second harmonic generation of thulium (Tm) was successful with Tm; LiNbO ₃ in 1997 (Johns
on et al. J. Appl. Phys. 40,2
97 (1969)). In recent years magnesium oxide (Mg
O) and neodymium (Nd) ions have been added simultaneously to achieve continuous oscillation of green light (Fan et al. J. Opt. Soc. Am. 3).
(1) 140 (1986)). However, even in this report, lithium niobate was heated to 152 ° C., and there was still a problem as a small and practical laser medium.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a small-sized laser oscillator capable of oscillating a green laser having a simple structure and a single crystal used as a laser medium.

[0007]

The above object of the present invention is achieved by using a lithium niobate single crystal containing a predetermined amount of neodymium and scandium as a laser medium of a solid-state laser oscillator.

That is, the present invention resides in a lithium niobate single crystal containing 0.01 to 0.5% by weight of neodymium ion and 0.05 to 0.5% by weight of scandium ion.

The lithium niobate single crystal of the present invention contains neodymium ions and scandium ions at the same time.
At this time, the neodymium ion concentration is 0.01 to 0.5% by weight, and the scandium ion concentration is 0.05 to 0.5% by weight.
It is necessary to be. If the neodymium ion concentration is less than this range, sufficient laser emission intensity cannot be obtained,
If it is more than this, the concentration quenching becomes remarkable, which is not preferable. Further, if the scandium ion concentration deviates from this range, the light damage resistance decreases.

To obtain a lithium niobate single crystal containing neodymium ions and scandium ions in this manner,
A predetermined amount of neodymium oxide and scandium oxide are mixed with a lithium niobate single crystal raw material such as lithium carbonate and diniobium pentoxide having a congruent composition, and the mixture is molded into a green compact, and a pulling method such as the Czochralski method, a floating method. A lithium niobate single crystal containing neodymium ions and scandium ions is obtained by the zone method, Bridgman method, liquid phase epitaxy method, or the like. Among these methods, the Czochralski method can be most preferably used.

Further, on the surface of a lithium niobate single crystal containing no neodymium ion or scandium ion,
Neodymium oxide and scandium oxide may be added by ion plantation or sputtering, and the scandium ion may be doped by a diffusion process such as heat treatment. This method is a preferable method considering that scandium or the like is an extremely expensive element and that the element is locally doped when manufacturing an optical element.

Next, the laser oscillator of the present invention uses the above-mentioned lithium niobate single crystal as a laser medium.

The laser oscillator of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing an example of a laser oscillator of the present invention. In the figure, 1 is a chopper, 2 is a lens, 3 is a mirror, and 4 is a laser medium (lithium niobate single crystal).

In FIG. 1, titanium ion-doped sapphire leather or a semiconductor laser is used as an excitation light source of 813 nm. As such an excitation light source,
The wavelength is not particularly limited as long as it is a wavelength that neodymium absorbs, but from the viewpoint of realizing a small element for the purpose of the present invention, a semiconductor laser is most preferably used.

This laser light is condensed by the lens 2, passes through the mirror 3 and is introduced into the laser medium (lithium niobate single crystal). This mirror 3 transmits almost all 813 nm laser light, and transmits 546 nm green light and 1092n.
Most of the laser light of m is reflected.

As described above, the laser medium 4 is made of lithium niobate single crystal containing a certain amount of neodymium ions and scandium ions.
It absorbs 13 nm laser light and oscillates 1092 nm laser light, and at the same time, it is the second harmonic of the 1092 nm laser light, 546, due to the nonlinear effect of the single crystal.
It also oscillates in nm green.

The lithium niobate single crystal used for the laser medium may have any shape, and the end face may be a plane perpendicular to the longitudinal axis or may be a Brewster cut. If the end face is not Brewster-cut, it is better to have a vapor deposition film that minimizes reflection at the excitation light, the fundamental oscillation wavelength and the second harmonic wavelength, as this will reduce the threshold and increase the efficiency of oscillation. Desirable for.

Further, it is desirable to control the temperature of this single crystal, and according to the knowledge of the present inventors, the phase matching temperature is 2 when the scandium ion concentration is 0.2% by weight.
It is 0 ° C.

In this way, the oscillated 1092 nm
Laser light and green light of 546 nm pass through the mirror 3,
The light is selectively separated by another mirror (not shown).

There are no particular restrictions on each part of such a laser oscillator, and it may be configured by appropriately combining plane mirrors and curved mirrors as described above. It is also possible to directly impart the function as a reflection mirror to one or both end faces of the crystal by coating.

[0021]

EXAMPLES The present invention will be specifically described below based on examples.

Example 1 A lithium niobate single crystal containing neodymium ions and scandium ions was grown by the Czochralski method. That is, a mixture of lithium carbonate (Li ₂ CO ₃ ) and diniobium pentoxide (Nd ₂ O ₅ ) having a congruent composition was mixed with 0.45 wt% (measured doping ion concentration) of neodymium oxide (Nd ₂ O ₃ ). 2% by weight
(Measured ion doping concentration) scandium oxide (Sc ₂
The raw material was added with O ₃ ). Growth rate is 0.8
mm / hr, the rotation speed was 20 rpm, and the growing atmosphere was air. The crystals obtained were pale purple, transparent and no inclusions were observed. After taking out the crystal from the growth furnace, it was immediately subjected to a single domainization treatment.

The sample used as the laser medium for the oscillation test was cut out from the above crystal. The size is crystal X, Y,
18 × 5 × 7mm in Z-axis direction and 109 in Z-plane
The coatings were applied so that the transmittance was as high as possible near 2 nm, 813 nm and 546 nm. The temperature of the sample (lithium niobate single crystal) was kept at 20 ° C. using a thermoelectric element. This temperature is the phase matching temperature of a lithium niobate single crystal containing 0.2% by weight of scandium ion.

Using this lithium niobate single crystal, FIG.
A laser oscillator like the above was manufactured. As an excitation light source, a titanium ion-containing sapphire (Ti; Al ₂ O ₃ ) laser was used by oscillating at 813 nm. The resonator has a radius of curvature of 1
It is composed of two reflecting mirrors of 00 mm. On the surface of the reflector, high reflection near 1092 nm and 546 nm, 8
A coating having a low reflection in the vicinity of 13 nm was applied.

The exciter propagates parallel to the X-axis and is deflected in the Z-axis direction, and this was focused into the crystal by using a lens having a focal length of 120 mm.

Oscillation at 546 nm is discontinuous (quasi-C) excited by using intermittent light even in the continuous (CW) mode.
It was also easily observed in W) mode. In continuous (CW) mode, the slope efficiency is 0.04%, the threshold is about 80mW,
In discontinuous (quasi-CW) mode, the threshold is 100 m
It was about W.

Output light (546 nm) with respect to the intensity of excitation light (813 nm) in the discontinuous oscillation and continuous oscillation.
2 to 3 are graphs showing the strength characteristics of the above.

In this embodiment, discontinuous (quasi-CW) is used.
Although only oscillation and continuous (CW) oscillation have been tried, the Q-switched green light is generated by applying an electric field in the Z-axis direction of the crystal by using the electro-optic effect of the widely known lithium niobate single crystal. Could be taken out.

[0029]

By constructing the laser oscillator of the present invention, green light can be directly obtained with one crystal. this is,
Compared to the method of converting the wavelength of neodymium laser, which is becoming mainstream at present, by using a non-linear crystal, it has an advantage that the number of crystals can be smaller. Further, the temperature of the crystal can be kept lower than in the case of using a lithium niobate single crystal containing both neodymium ion and magnesium ion at the same time. In particular, a crystal having a scandium ion concentration of 0.2% by weight has a phase matching temperature of about room temperature and is close to the operating temperature of a semiconductor laser which is an excitation light source, which is advantageous for downsizing the device.

Further, when a lithium niobate single crystal containing neodymium ions and magnesium ions is used, the oscillation direction of the fundamental wave is σ in order to oscillate with green light.
It was necessary to deflect (perpendicular to the Z-axis), and it was necessary to insert a deflection selection element in the resonator for its control. However, when the lithium niobate single crystal containing neodymium ions and scandium ions of the present invention is used, it does not need to do so because it oscillates by σ deflection by itself. This point is also a great advantage for downsizing and simplification of the entire device.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of a laser oscillator of the present invention.

FIG. 2 is an output light (546 nm) with respect to a pumping light (813 nm) intensity in discontinuous (quasi-CW) oscillation.
A graph showing the strength characteristics of.

FIG. 3 shows excitation light (813n) in continuous wave (CW) oscillation.
m) A graph showing the intensity characteristics of output light (546 nm) with respect to intensity.

[Explanation of symbols]

1: Chopper, 2: Lens, 3: Mirror, 4: Laser medium (lithium niobate single crystal).

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kiyoji Yamagishi 2 1333, Ojihara, Ageo City, Saitama Prefecture Mitsui Kinzoku Mining Co., Ltd. Research Institute (72) Kenji Kitamura 1-1, Namiki, Tsukuba, Ibaraki Prefecture (72) Inventor Shigeyuki Kimura 1-1 Namiki, Tsukuba City, Ibaraki Prefecture Science and Technology Agency Inorganic Materials Research Institute (72) Nobuo Ii 1-1 Namiki, Tsukuba City, Ibaraki Institute of Inorganic Materials Science

Claims (2)

[Claims] 1. A lithium niobate single crystal containing 0.01 to 0.5% by weight of neodymium ion and 0.05 to 0.5% by weight of scandium ion. 2. A laser oscillator using the single crystal according to claim 1 as a laser medium.