Solid-state laser device

Details Solid-state laser device Solid-state laser device

2003-02-10

2004-11-02

Wong, Don (Department: 2828)

Coherent light generators

Particular resonant cavity

Plural cavities

C372S021000, C372S022000, C372S068000, C359S326000

Reexamination Certificate

active

06813306

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor laser device, in particular, to a solid-state laser device, and further relates to a solid-state laser device which is oscillated in two wavelengths by a resonator and converts the wavelength in the resonator.
A diode pumped solid-state laser is known, which uses intracavity type SHG mode to convert frequency of a laser beam from a fundamental frequency.
Referring to
FIG. 5
, description will be given on general features of the diode pumped solid-state laser of one-wavelength oscillation.
In
FIG. 5
, reference numeral
2
denotes a light emitter, and
3
is an optical resonator. The light emitter
2
comprises an LD light emitter
4
and a condenser lens
5
. Further, the optical resonator
3
comprises a laser crystal
8
where a dielectric reflection film
7
is formed, a nonlinear optical medium (NLO)
9
, and a concave mirror
12
where a dielectric reflection film
11
is formed. A laser beam is pumped at the optical resonator
3
, and the laser beam is outputted by resonation and amplification. As the laser crystal
8
, Nd:YVO
4
may be used. As the nonlinear optical medium
9
, KTP (KTiOPO
4
; titanyl potassium phosphate) may be used.
Further description will be given below.
A laser light source
1
is used to emit a laser beam with a wavelength of 809 nm, for instance, and the LD light emitter
4
, i.e. a semiconductor laser, is used. The LD light emitter
4
has the function as a pumping light generator for generating an excitation light. The laser light source
1
is not limited to the semiconductor laser, and any type of light source means can be adopted so far as it can emit a laser beam.
The laser crystal
8
is used for amplification of light. As the laser crystal
8
, Nd:YVO
4
with an oscillation line of 1064 nm is used. In addition, YAG (yttrium aluminum garnet) doped with Nd
3+
ion or the like is adopted. YAG has oscillation lines of 946 nm, 1064 nm, 1319 nm, etc. Also, Ti (sapphire) with oscillation lines of 700-900 nm can be used.
On the LD light emitter
4
side of surfaces of the laser crystal
8
, a first dielectric reflection film
7
is formed. The first dielectric reflection film
7
is highly transmissive to a laser beam from the LD light emitter
4
and is highly reflective to an oscillation wavelength of the laser crystal
8
, and it is also highly reflective to SHG (second harmonic generation).
The concave mirror
12
is designed to face to the laser crystal
8
. The laser crystal
8
side of surfaces of the concave mirror
12
is fabricated in form of a concaved spherical mirror having an adequate radius and a second dielectric reflection film
11
is formed on it. The second dielectric reflection film
11
is highly reflective to the oscillation wavelength of the laser crystal
8
, and it is highly transmissive to SHG (second harmonic generation).
As described above, when the first dielectric reflection film
7
of the laser crystal
8
is composed with the second dielectric reflection film
11
of the concave mirror
12
and the laser beam from the LD light emitter
4
is pumped to the laser crystal
8
via the condenser lens
5
, the light is reciprocally projected between the first dielectric reflection film
7
of the laser crystal
8
of and the second dielectric reflection film
11
. Thus, the light can be confined for longer time, and the light can be resonated and amplified.
The nonlinear optical medium
9
is inserted in the optical resonator, which comprises the first dielectric reflection film
7
of the laser crystal
8
and the concave mirror
12
. When an intensive coherent light such as a laser beam enters the nonlinear optical medium
9
, a second harmonic wave to double the light frequency is generated. The generation of the second harmonic wave is called “second harmonic generation (SHG)”. As a result, a laser beam with a wavelength of 532 nm is emitted from the laser light source
1
.
In the laser light source
1
as described above, the nonlinear optical medium
9
is inserted into the optical resonator, which comprises the first dielectric reflection film
7
of the laser crystal
8
and the concave mirror
12
, and it is called an intracavity type SHG. Because conversion output is proportional to square of excited photoelectric power, there is such effect that high light intensity in the optical resonator can be directly utilized.
Further, a type of solid-state laser device is known, by which an entered laser beam of a fundamental frequency is oscillated to two different wavelengths and these are further converted to different frequencies by using sum frequency mixing (SFM) and differential frequency mixing (DFM).
Description will be given on the solid-state laser device as described above referring to FIG.
6
. In
FIG. 6
, the LD light emitter
4
and the condenser lens
5
are omitted.
As seen from the LD light emitter
4
, there are arranged a concave mirror
12
, a laser crystal
8
, a first plane reflection mirror
14
, a nonlinear optical medium
9
, a second plane reflection mirror
15
, and a third plane reflection mirror
16
.
The concave mirror
12
is highly transmissive to a wavelength &lgr;1 (809 nm in the figure), and it is highly reflective to a wavelength &lgr;1 (1342 nm in the figure) and a wavelength &lgr;2 (1064 nm in the figure). Further, the first plane reflection mirror
14
is highly reflective to SFM (wavelength &lgr;3=593 nm in the figure) and is highly transmissive to the wavelengths &lgr;1 and &lgr;2. The second plane reflection mirror
15
is highly transmissive to the wavelengths &lgr;3 and &lgr;2, and it is highly reflective to the wavelength &lgr;1. The third plane reflection mirror
16
is highly transmissive to the wavelength &lgr;3 and is highly reflective to the wavelength &lgr;2.
The excitation light &lgr;i entered via the concave mirror
12
excites the laser crystal (Nd:YVO
4
). Among the natural released light beams, the light beams with the wavelengths &lgr;1 and &lgr;2 are pumped and resonated between the concave mirror
12
and the second plane reflection mirror
15
and between the concave mirror
12
and the third plane reflection mirror
16
. The wavelength of &lgr;1 is excited and amplified, and the wavelength of &lgr;2 is excited and amplified. Further, the laser beams with both wavelengths pass through the nonlinear optical medium
9
. As a result, sum frequency &lgr;3 of both wavelengths can be obtained, and the laser beams pass through the third plane reflection mirror
16
and are projected.
In case of sum frequency mixing (SFM), there exists a relationship: 1/&lgr;3=1/&lgr;1+1/&lgr;2. By selecting the nonlinear optical medium
9
, differential frequency mixing can be obtained. In this case, there exists a relationship: 1/&lgr;3=1/&lgr;1−1/&lgr;2 (where &lgr;1<&lgr;2).
In the frequency conversion of the above described solid-state laser device for generating sum frequency mixing (SFM) and differential frequency mixing (DFM), it is advantageous in that wavelength conversion can be achieved with high efficiency by arranging the nonlinear optical medium
9
in the optical resonator.
A conventional type example as described above is written, for instance, in F. chen. and S. W. Tssi: Opt. Lett. 27 (2002), 397.
In the solid-state laser device shown in
FIG. 6
, sum frequency mixing (SFM) and differential frequency mixing (DFM) are generated, and frequency conversion is performed. It is advantageous in that wavelength conversion can be carried out with high efficiency, while it has the following disadvantages:
The laser beam, which can be inputted to the laser crystal
8
, is under excitation input limitation at a breakdown threshold value of the crystal, and it is difficult to have high output.
In order to raise excitation efficiency, the fundamental wave with the wavelength &lgr;1 is needed to be on the same optical axis as the fundamental wave with the wavelength &lgr;2. Because the concave mirror
12
, the second plane reflection mirror
15
and the third p

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