Optical: systems and elements – Optical frequency converter – Parametric oscillator
Reexamination Certificate
2000-05-10
2003-03-18
Lee, John D. (Department: 2874)
Optical: systems and elements
Optical frequency converter
Parametric oscillator
C372S022000
Reexamination Certificate
active
06535327
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates generally to optical parametric oscillators and particularly to laser systems comprising optical parametric oscillators.
Wavelength tunable laser systems are frequently constructed with optical parametric oscillators. Optical parametric oscillators are commonly constructed with a crystal having nonlinear optical properties disposed between two mirrors, referred to as an optical cavity. Referring generally to
FIG. 1
, an optical parametric oscillator can include an optical cavity
10
comprising two parallel plane mirrors
20
a
and
20
b
, whose surfaces are treated to be reflective or transmissive, based on the wavelength of incident light. A nonlinear crystal
30
is disposed between mirrors
20
a
and
20
b
. In operation, a laser beam
40
, referred to as the pump or pumping laser beam, passes through the back of first mirror
20
a
and into nonlinear crystal
30
. Nonlinear crystal
30
converts laser beam
40
into two coherent waves of a signal frequency (f
s
) and a complementary or idler frequency (f
i
), such that the frequency (f
p
) of pump laser beam
40
is equal to the signal frequency plus the idler frequency (f
p
=f
s
+f
i
)
Simple optical parametric oscillators can be constructed so that the inner facing surfaces of mirrors
20
a
and
20
b
are treated to reflect the signal beam. The inner surface of first mirror
20
a
is generally treated to reflect the idler beam. However, the inner surface of second mirror
20
b
is generally treated to transmit the idler beam outside of the optical cavity. Alternatively, optical parametric oscillators can be constructed in a “doubly resonant configuration”, in which the mirrors are treated to reflect one of the beams (i.e., the signal beam) completely and second mirror
20
b
is constructed to transmit one of the beams (i.e., the idler beam) only partially and to reflect a portion of the idler beam back into the crystal. This “doubly resonant” configuration permits the use of pump beams with a lower intensity, while still achieving sufficient optical activity by the nonlinear crystal and transmitting an appropriate wave from the optical cavity.
When an appropriate crystal
30
with appropriate birefringence properties is selected, the frequency of the beam emitted by the OPO can be tuned by adjusting the orientation of the optical axis (crystalline axis) of crystal
30
with respect to the optical axis of the OPO. In alternative embodiments, two or more nonlinear crystals can be used in place of single crystal
30
.
Optical parametric oscillators can have drawbacks. For example, the longwave tuning range of existing OPOs has generally been limited to the 4 to 5 &mgr;m range. This is not suitable for many scientific applications.
Accordingly, it is desirable to provide a laser system including an optical parametric oscillator which can emit beams that are widely and easily tunable within desired frequency bands and are of a relatively low power. It is also desirable to provide a laser system including an optical parametric oscillator which overcomes other drawbacks and deficiencies of the prior art.
SUMMARY OF THE INVENTION
Generally speaking, in accordance with the invention, an optical parametric oscillator and a laser system including an optical parametric oscillator, is provided for producing widely tunable coherent light over about 6 &mgr;m, such as in the range of at least about 7.5 &mgr;m to 16 &mgr;m and even about the 7 to 18 &mgr;m range. Optical parametric oscillators in accordance with the invention advantageously include CdGeAs
2
(CGA) crystals. When grown properly, such crystals, in accordance with the invention, can exhibit exceptionally small (<0.1 cm
−1
) losses in intensity. Laser systems in accordance with the invention can include CO
2
lasers as the pump beam and frequency doublers or changers, such as CGA crystals.
Accordingly, it is an object of the invention to provide improved optical parametric oscillators.
Another object of the invention is to provide improved wavelength tunable laser systems.
Another object of the invention is to provide an improved method of making an optical parametric oscillator and laser system.
The invention accordingly comprises the features of construction, combinations of elements, and the arrangements of parts and the steps for effecting the foregoing, and the scope of the invention will be indicated in the claims.
REFERENCES:
patent: 4011462 (1977-03-01), Piltch et al.
patent: 4107544 (1978-08-01), Kildal et al.
patent: 4450356 (1984-05-01), Murray et al.
patent: 4955699 (1990-09-01), Singh et al.
patent: 5110430 (1992-05-01), Eerkens
Vodopyanov et al, “Two-Photon Absorption in GaSe And CdGeAs2”, Summaries Of Papers Presented At The Conference On Lasers And Electro-Optics 1999 (CLEO '99), Baltimore MD (USA), pp. 477-478, May 23-28, 1999.*
Schunemann, “Growth of CdGeAs2 for Mid-to Far-IR Frequency Conversion”, 1996 Quantum Electronics and Laser Science Conference (QELS '96), paper Tul4, pp. 94-95, Jun. 1996.*
Vodopyanov et al, “Efficient Difference-Frequency Generation of 7-to 20&mgr;m Radiation Using CdGeAs2”, 1998 Conference on Lasers and Electro-Optics (CLEO '98), paper CFC7, p. 509, May 1998.
Lee John D.
Picarro, Inc.
Stroock & Stroock & Lavan LLP
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