Second harmonic, single-mode laser

Details Second harmonic, single-mode laser Second harmonic, single-mode laser

1999-07-13

2001-09-25

Scott, Jr., Leon (Department: 2881)

Coherent light generators

Particular beam control device

Mode discrimination

C372S022000, C372S098000

Reexamination Certificate

active

06295305

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an internal resonance-type, second harmonic, single-mode laser comprising a nonlinear optical crystal inside a solid-state laser resonator comprising a Cr-doped fluoride laser crystal, particularly to an internal resonance-type, second harmonic, single-mode laser for stably generating single-mode oscillation.
PRIOR ART
Demand is mounting for small, high-power, short-wavelength lasers to increase the recording density of optical disks and the resolution of optical measurement devices, etc. One of the promising candidates for light sources for such lasers is a second harmonic generation (SHG) laser using a nonlinear optical crystal. Particularly promising is the excitation of an internal resonance-type SHG laser comprising a nonlinear optical crystal inside the laser resonator by a semiconductor laser, because of small size and high-power output. A laser comprising a Cr-doped fluoride laser crystal such as Cr:LiSAF (Cr
3+
-containing LiSrAlF
6
), Cr:LiCAF (Cr
3+
-containing LiCaAlF
6
), Cr:LiSGaF (Cr
3+
-containing LiSrGaF
6
), etc. and excited by a semiconductor laser can generate oscillation in a wide wavelength range. For instance, the oscillation wavelength of a Cr:LiSAF crystal is ranging from 780 nm to 1000 nm. Accordingly, an internal resonance-type SHG laser comprising a combination of the Cr:LiSAF crystal and the nonlinear optical crystal can generate output in as wide a short-wavelength range as 390-500 nm. To achieve phase matching of the nonlinear optical crystal from a wide range of wavelengths of the oscillated laser beam by the Cr:LiSAF crystal, a birefringent filter is disposed in the resonator to give loss to the oscillated wavelengths except for the desired wavelength to be selected (WO 97/21259).
FIG. 2
shows a typical example of the laser structure as disclosed by WO 97/21259. A coating mirror
9
formed on an input-side surface of the Cr:LiSAF crystal
5
and an output mirror
4
constitute a resonator, and an exciting laser beam
21
is supplied from an external exciting laser beam source to the resonator to cause the laser oscillation of the Cr:LiSAF crystal, which generates a laser beam
22
that is then converted to an SH beam
23
by a nonlinear optical crystal
8
. In this case, the wavelengths of the laser beam
22
generated by the oscillation of the Cr:LiSAF crystal
5
are selected by a birefringent filter
6
, to produce a laser beam that matches the phase-matching wavelength of the nonlinear optical crystal
8
.
However, the wavelength selection by the birefringent filter
6
causes multi-mode oscillation because its wavelength selection width is wider than the longitudinal-mode interval of the resonator. If a fundamental wave is multi-mode oscillated in the internal resonance-type SHG laser, a mode-competing phenomenon takes place in the resonator, making unstable the SHG output at the time of wavelength conversion in the nonlinear optical crystal and causing noises called “SHG noises.”
To suppress the SHG noises, it is effective to cause single-mode oscillation of the fundamental wave. Thus, Japanese Patent laid-Open No. 9-307160 proposed the insertion of an etalon into the resonator to make the fundamental wave narrower than the wavelength selection width of the birefringent filter, thereby causing oscillation in only one resonator mode, namely a single-mode oscillation technique.
However, in a single-mode laser comprising a combination of the birefringent filter and the etalon in its resonator, optimum conditions such as wavelength selection width, wavelength interval etc. for good single-mode oscillation are not known, and thus an optimum operation range for single-mode oscillation cannot easily be found. Thus, stable single-mode oscillation cannot easily be obtained. Also, if the operation range of single-mode oscillation were widened, sufficient SH output would not be able to be obtained.
OBJECT AND SUMMARY OF INVENTION
Accordingly, an object of the present invention is to provide an internal resonance-type, second harmonic, single-mode laser comprising a laser crystal capable of oscillating in a wide wavelength range, which can stably produce high-power output.
The second harmonic, single-mode laser according to the present invention comprises a resonator comprising a Cr-doped fluoride laser crystal, first and second wavelength-selecting elements and a nonlinear optical crystal between a pair of laser mirrors, a wavelength-selecting width of the first wavelength-selecting element being {fraction (1/30)} or less of that of the second wavelength-selecting element, whereby only one of wavelengths passing through the first wavelength-selecting element is oscillated, with the remaining wavelengths attenuated to a level that cannot maintain oscillation.
In a preferred embodiment of the present invention, the second harmonic, single-mode laser comprises a resonator comprising a Cr-doped fluoride laser crystal, first and second wavelength-selecting elements and a nonlinear optical crystal between a pair of laser mirrors, wherein a wavelength-selecting width of the first wavelength-selecting element is {fraction (1/30)} or less of that of the second wavelength-selecting element; wherein the first wavelength-selecting element is provided with a reflection coating having a reflectivity of 10-3% to the oscillated laser beam supplied from the Cr-doped fluoride laser crystal, such that the wavelength selection width of the first wavelength-selecting element is 0.02-0.03 nm; wherein a wavelength interval in the oscillation wavelength range of the first wavelength-selecting element is 08-1.3 nm; and wherein a wavelength selection width of the second wavelength-selecting element is 1.0-1.6 nm.


REFERENCES:
patent: 5627849 (1997-05-01), Baer
patent: 5657341 (1997-08-01), Hyuga
patent: 6047010 (2000-04-01), Makio et al.
patent: 09307160 A (1997-11-01), None
patent: WO 97/21259 (1997-12-01), None

Affiliated with

Also associated with

Rating

Second harmonic, single-mode laser does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Second harmonic, single-mode laser, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Second harmonic, single-mode laser will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2478031