Nondegenerate Optical Parametric Chirped Pulse Amplification Page: 3 of 7
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Nondegenerate optical parametric
chirped pulse amplification
Igor Jovanovic1'2, Christopher A. Ebbersl, Brent C. Stuart, Mark R. Hermann[, and E. C. Morse2
'Lawrence Livermore National Laboratory, Mail Code L-490, 7000 East Avenue, Livermore, California 94550
2Department of Nuclear Engineering, University of California at Berkeley, Berkeley, California 94720
jovanovicl @llnl.gov
Abstract: We present the first recompression of amplified pulses in a highly nondegenerate
optical parametric chirped pulse amplifier. 60-fs recompressed pulse width and up to 2 mJ pulses
were obtained in our experiments.
2001 Optical Society of America
OCIS codes: (190.4970) Parametric oscillators and amplifiers; (140.7090) Ultrafast lasers
Generation and amplification of ultrashort laser pulses has been at the forefront of laser research in the recent period,
driven primarily by newly accessible physics phenomena and commercial applications such as materials processing.
The interest in optical parametric chirped pulse amplification (OPCPA) [1] for ultrashort pulse amplification has
been motivated by its favorable properties. Largp single-pass gain achievable in a -cm length of nonlinear material
pumped by nanosecond pump laser eliminates the need for regenerative amplification. Broad bandwidth capabilities
and scalability make OPCPA a possible amplification technology for future multi-PW sources [2]. Absence of
thermal load should allow short pulse amplification up to kW-level average power. While the ultrashort
amplification capabilities of optical parametric amplifiers (OPAs) have been demonstrated down to 5 fs, the
compression of ultrashort (<100 fs) pulses in thick OPCPA crystals remains largely unexplored. Here, we present
the first pulse compression in highly nondegenerate OPCPA and obtain the shortest pulses produced in OPCPA to
date.
The design of our OPCPA system is presented in Fig. 1. A.mode-locked oscillator, which produces 20-fs pulses
centered at 820 nm, is used as a seed source. An all-reflective stretcher is used to stretch the seed pulses to 600 ps,
with a spectral cut-off width in excess of 100 nm. The OPA consists of two antireflection-coated beta-barium borate
(BBO) crystals. The crystals are cut at 23.80 to facilitate type I phase matching at an external noncollinear angle of
3.70. The noncollinear angle is optimized numerically to maximize the gain bandwidth. The length of each crystal is
15 mm, and they have a wedged output surface to eliminate parasitic oscillation. The pump beam is relay imaged
between the two crystals and the beam diameter is adjusted to 3 mm, for a peak intensity near 450 MW/cm2. We
obtained a maximum gain of 4x106 from the OPA when the noncollinear plane was chosen to be perpendicular to
the principal plane of the crystal. The result were pulses with energies of up to 2 mJ amplified in a single pass
through only 30 mm of gain material. The measured seed and amplified signal spectra are shown in Fig 2. We
observe a shift of the center wavelength to 830 nm, which is consistent with the gain bandwidth in nondegenerate
BBO OPA, which is centered at longer wavelengths (near 850 nm). The small bandwidth narrowing (<2 nm) at the
FWHM observed when the OPA operates far below saturation (0.5 mJ) can be attributed to this spectral shift. At the
point near saturation (2 mJ), the spectrum is modified further and the amplified FWHM is increased to 35 nm.
Spectral broadening is the result of different rate of nonlinear conversion for the spectral components of different
initial intensity. We recompressed our pulses in a single-grating compressor, and the autocorrelation trace is shown
in Fig. 3. The measured FWHM autocorrelation of the recompressed pulse is 104 fs, which is nearly 2 times longer
than the FWHM of the calculated autocorrelation of the transform-limited pulse with the measured spectrum (Fig.
2). With the inclusion of the spectral phase in the system, the calculated FWHM of the autocorrelation is 108 fs,
which is within our experimental error, indicating that we produced 60-fs pulses.
In summary, we report for the first time the compression of pulses amplified in nondegenerate OPCPA. The
reported 60-fs pulses are the shortest pulses reported to date produced in an OPCPA system. A careful compensation
of spectral phase in our system should enable 30-fs transform-limited pulses.
This work was performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National
Laboratory under Contract No. W-7405-Eng-48.
This work was performed under the auspices of the U.S. Department of Energy by the University of California,
Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.
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Jovanovic, I.; Ebbers, C.; Stuart, B.; Hermann, M. & Morse, E. Nondegenerate Optical Parametric Chirped Pulse Amplification, article, November 7, 2001; Livermore, California. (https://digital.library.unt.edu/ark:/67531/metadc734126/m1/3/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.