Coherent light generators – Particular pumping means – Pumping with optical or radiant energy
Reexamination Certificate
2000-07-21
2002-12-03
Ip, Paul (Department: 2828)
Coherent light generators
Particular pumping means
Pumping with optical or radiant energy
C372S006000, C372S068000, C372S041000
Reexamination Certificate
active
06490309
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a laser-diode-pumped solid-state laser apparatus. The present invention also relates to a laser-diode-pumped fiber laser apparatus. The present invention further relates to a laser-diode-pumped fiber laser amplifier.
2. Description of the Related Art
(1) Ultraviolet Laser
Highly efficient, high output power ultraviolet lasers which continuously oscillate in the ultraviolet wavelength range are required, for example, for applications in ultraviolet lithography, fluorometric analysis of organic cells, and the like. GaN-based compound semiconductor lasers having an active layer made of an InGaN, InGaNAs, or GaNAs material are known as lasers which oscillate in the ultraviolet wavelength range. Recently, GaN-based compound semiconductor lasers which can continuously oscillate for a thousand hours at the wavelength of 400 nm with output power of several milliwatts are provided.
However, the current GaN-based compound semiconductor lasers cannot emit laser light with output power of 100 mW or more by a single transverse mode, which is required in many applications. In addition, the oscillation efficiency in the current GaN-based compound semiconductor lasers which emit laser light having wavelengths of 380 nm or below is low, and the lifetimes of such semiconductor lasers are very short.
On the other hand, wavelength-conversion solid-state lasers which output ultraviolet laser beams having wavelengths of 400 nm or below are known. In these wavelength-conversion solid-state lasers, wavelengths of laser oscillation light are shortened to the ultraviolet wavelengths by second harmonic generation (SHG) or third harmonic generation (THG) using nonlinear optical crystals.
However, solid-state laser mediums which can efficiently oscillate in the wavelength range of 700 to 800 nm have not yet been found. Therefore, it is difficult to obtain high output power from the wavelength-conversion solid-state lasers in which the wavelengths of the laser light are shortened by second harmonic generation (SHG).
In addition, the efficiency of the wavelength-conversion solid-state lasers in which the wavelengths of the laser light are shortened by third harmonic generation (THG) is essentially low, and the current THG wavelength-conversion solid-state lasers can oscillate in only a pulse mode. In order to realize continuous oscillation, it is necessary to maintain resonance of SHG light of the fundamental wave, and highly accurate temperature adjustment of a resonator with a precision of 0.01iC is required for oscillation of the THG light. However, such accurate temperature adjustment is practically difficult in terms of cost.
(2) Blue and Green Lasers
Gas-laser-pumped solid-state laser apparatuses in which a Pr
3+
-doped solid-state laser crystal is pumped with a gas laser such as an Ar laser are known as disclosed in Journal of Applied Physics, vol. 48, No. 2, pp.650-653 (1977), and Applied Physics, B58, pp.149-151 (1994). In addition, a solid-state laser apparatus in which a Pr
3+
-doped solid-state laser crystal is pumped by second harmonic (SH) light from a lamp-pumped solid-state laser is known, as disclosed in “Advanced Solid-State Laser,” OSA TOPS, vol.19, pp.34-35, the Optical Society of America, 1998. In these solid-state laser apparatuses, it is possible to generate a laser beam in a blue wavelength range of 470 to 490 nm by a transition from
3
P
0
to
3
H
4
. It is also possible to generate a laser beam in a green wavelength range of 520 to 550 nm by a transition from
3
P
1
to
3
H
1
. Therefore, the above solid-state laser apparatuses can be used as a light source for recording a color image in a color sensitive material.
The light sources for use in recording a color image in a color sensitive material are required to be small in size, light in weight, and inexpensive. However, the above gas-laser-pumped and lamp-pumped solid-state laser apparatuses using the Pr
3+
-doped solid-state laser crystals are not suitable for use in recording a color image in a color sensitive material since the pumping light sources in these solid-state laser apparatuses are large, heavy, and expensive.
In addition, a solid-state laser apparatus in which a Pr
3+
-doped solid-state laser crystal is pumped by a blue laser beam emitted from an SHG laser apparatus is known as disclosed by Andy Clarkson, “Visible and UV Sources,” Technical Digest of CLEO '99, University of Southampton, 1999.
However, the above SHG-pumped solid-state laser apparatuses using the Pr
3+
-doped solid-state laser crystals are also not suitable for use in recording a color image in a color sensitive material since the pumping light sources in the SHG-pumped solid-state lasers are large, heavy, and expensive.
As another solid-state laser apparatus which emits a laser beam having a wavelength in the blue or green wavelength range, Japanese Unexamined Patent Publication No. 4(1992)-318988 discloses a laser-diode-pumped SHG laser apparatus in which a solid-state laser beam is converted into a second harmonic, i.e., the wavelength of the solid-state laser beam is reduced by half by arranging a nonlinear optical crystal in a resonator.
However, the efficiency of wavelength conversion in the current laser-diode-pumped SHG laser apparatuses in which a wavelength of a solid-state laser beam is reduced by using a nonlinear optical crystal is not sufficiently high, and therefore it is difficult to obtain high output power. In addition, in such laser-diode-pumped SHG laser apparatuses, an etalon or the like is inserted for limiting the oscillation mode to a single mode. Therefore, loss in the resonator is great, and thus achievement of high output power becomes more difficult. Further, in order to match phases in the wavelength conversion, highly accurate temperature control is required, and therefore the outputs of the laser-diode-pumped SHG laser apparatuses are not stable. Moreover, since the numbers of parts are increased by the provision of the nonlinear optical crystal and the etalon, the laser-diode-pumped SHG laser apparatuses are expensive.
Recently, InGaN-based compound laser diodes and ZnMgSSe-based compound laser diodes which emit laser beams in the blue and green wavelength ranges have been developed.
Since, the oscillation wavelengths of the InGaN-based compound laser diodes increase with increase in the indium content, theoretically it is possible to obtain laser beams in the blue wavelength range of 470 to 490 nm, or laser beams in the green wavelength range of 520 to 550 nm. However, since the quality of the crystal deteriorates with the increase in the indium content, it is practically impossible to sufficiently increase the indium content, and the upper limit of the lengthened wavelength is about 450 nm.
In addition, blue light can be obtained by laser diodes having an active layer made of an InGaNAs or GaNAs material. The oscillation wavelengths in these laser diodes can also be increased by doping the active layer with arsenic. However, since the quality of the crystal deteriorates with the increase in the arsenic content, the upper limit of the wavelength realizing high output power is about 450 to 460 nm.
Further, the current ZnMgSSe-based compound laser diodes cannot oscillate continuously at wavelengths below 500 nm at room temperature, and the lifetimes are at most a hundred hours.
Japanese Unexamined Patent Publication No. 11(1999)-17266, which is assigned to the present assignee, discloses a laser-diode-pumped solid-state laser apparatus which is inexpensive, and can emit a laser beam in the blue or green wavelength range with high efficiency, high output power, and high output stability. In this laser-diode-pumped solid-state laser apparatus, a Pr
3+
-doped solid-state laser crystal is pumped with an InGaN-based compound laser diode having an active layer made of an InGaN-based compound, or an InGaNAs-based compound laser diode having an active layer made of an InGaNAs-based compound, or a GaNAs-bas
Katoh Takayuki
Okazaki Yoji
Fuji Photo Film Co. , Ltd.
Ip Paul
Menefee James
Stroock & Stroock & Lavan LLP
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