Broadly Turnable Pump-Resonant Diode-Pumped CW PPLN OPO Page: 3 of 4
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High Power Tunable Diode
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4-371
Figure 1 The OPO system consists of a high power tunable diode pump laser, optical isolators, mode-matching optics,
a variable attenuator, the linear cavity OPO and cavity locking electronics.The OPO is a two-mirror standing wave symmetric
resonator with 50 mm radius of curvature mirrors and a
50 mm long PPLN crystal. The physical cavity length of
122 mm produces a waist e-2 radius of about 70 and 60 m for
the signal and pump waves. The input mirror (Ml) is coated
for 86% reflectivity at the 806 nm pump wavelength, high
reflectance at the 1.03 to 1.3 pm signal wave, and for low
reflection at the 3 to 3.5 pm idler wave. The output mirror
(M2) is coated for high reflectance at the pump and signal
waves and low reflectance at the idler wave. The input mirror
is mounted on a piezoelectric transducer (PZT). The 0.5 mm
thick PPLN crystal has poled regions with poling periods
ranging from 20.5 to 22.0 m. Its faces were antireflection
coated for the signal, pump and idler. The PPLN is housed in
an oven that permits its temperature to be varied from about
100C to 200C; photorefractive damage precludes OPO
operation at temperatures below about 100C.
The cavity can be locked to the pump frequency by driving
the PZT with a signal derived from a photodiode that samples
the reflected pump light. Initially the PZT was dithered at
3 kHz and lockin detection at twice that frequency produced
an error signal suitable to minimize the pump reflection. As
has been noted by others, high bandwidth is required because
of the potential for small but rapid temperature changes in the
crystal with cavity tuning. In our case the cavity was found
to rapidly detune from resonance when it was tuned from the
low frequency side to near resonance with the pump source;
however, when tuned from the high frequency side, the cavity
was stable until resonance was achieved. We found that the
bandwidth afforded by this system was not sufficient to lock
the operating OPO. While long term operation of the OPO at
peak performance requires the use of the cavity lock loop, the
OPO can be operated manually for brief periods (tens of
seconds) near the resonance condition without the servo loop
at a small penalty in output power. Indeed most of the data
presented in this paper was taken without closing the lockingcircuit and by manually tuning the cavity resonance to be
slightly greater than the pump frequency.
Results
The dots in Figure 2 show the observed output idler power
versus the incident pump power for the diode-pumped pump-
resonant OPO. At 3.3 pm, up to 20 mW of idler was emitted
from the output mirror with an input power of 410 mW. The
oscillation threshold was approximately 100 mW. A similar
OPO, pumped by the high quality beam from a Ti:SAP laser
achieved oscillation threshold at about 40 mW with the cavity
lock loop activated; in that case we used a dither frequency of25
20E
0
a,
L;0
15
105-
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0Thresh
-100mwMeasurements
Model
0
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old
,0150
300
450
Pump Power Incident on Input Coupler (mW)
Figure 2 The idler output power at 3.3 pm
measured in the free running mode and the model
prediction.Seamans 2
Detector
Optical Isolators WP POL
5 cm
M1
PZT
OPO' M2
Output
Cavity
Lock
Circuit-
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Alford, W.J.; Bowers, Mark S.; Raymond, T.D. & Seamans, J.F. Broadly Turnable Pump-Resonant Diode-Pumped CW PPLN OPO, article, April 29, 1999; Albuquerque, New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc711124/m1/3/: accessed April 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.