LBO
doubler
532 nm
output
Turning
mirrors
1064 nm
output
Optical
isolator
BBO
Q-switch
Thin-flm
polarizer
Cavity
mirrors
Crossed-head
slab gain
module
Seed input
Fast rise/fall
Q-switch driver
Fiber-coupled
seeder
λ/4
waveplate
newsbreaks
Single-shot broadband mid-IR spectra
measured in the visible via upconversion
Researchers at the
Institute for Molecular Science
(Okazaki, Japan),
National Chiao
Tung University
(Hsinchu, Taiwan),
and Kagawa University (Takamatsu,
Japan) have demonstrated single-shot broadband
mid-IR spectroscopy using a conventional visible dispersive spectrometer; they
do this by chirped-pulse upconversion of broadband IR spectra into the visible
region. The results (red curves) compare well to results using a conventional
mid-IR Fourier spectrometer (green curves) for analyzing films of polystyrene
(top) and polyvinyl alcohol (bottom).
The entire mid-IR spectrum from 200 to 5500 cm- 1 ( 1. 8 to 50 µm) was up-converted via four-wave difference-frequency generation (FWDFG) in xenon
gas. First, a subcycle broadband mid-IR pulse was created from
Ultrafast detector
senses both near-IR
and terahertz pulses
A photodetector has been created that
responds with precise timing to both
near-IR and terahertz radiation. Developed by researchers at the University of
Erlangen-Nuremberg, Technical University Dresden, and Helmholtz-Zentrum
Dresden-Rossendorf (all in Germany)
and the University of California, Santa
Barbara, the detector is designed for simultaneously resolving optical and terahertz pulses for terahertz-pump/op-tical-probe experiments, as well as
characterizing high-peak-power ( 30 k W)
terahertz pulses.
The field-effect-transistor (
FET)-based detector has an area of 345 µm2
and is located on the flat of a plano-convex silicon lens; near-IR light access-es the device directly through air, while
terahertz radiation is incident from the
opposite direction and
Laser-diode-based amplifier suits satellite laser ranging
Instead of using an expensive modelocked Nd:YAG laser as the
seed source, NASA Goddard Space Flight Center (Greenbelt,
MD) and American University ( Washington, DC) scientists used
commercially available laser diodes to build a small-footprint regenerative amplifier suited for ground-based satellite laser-rang-ing applications.
With a goal of creating 1 mJ of 532 nm light at a 2 kHz rep-
etition rate with pulsewidths of less than 200 ps, the setup be-
gins with a 1064 nm narrowband laser diode driven in short-
pulse mode (0.2–0.4 ns seed pulsewidths). The input enters the
amplifier gain unit consisting of two Brewster-cut Nd:YAG la-
ser slabs oriented 90º to each other to simplify optical correc-
tion and create a symmetrical thermal lens effect and each
pumped with an 808 nm laser-diode array. Laser-diode tem-
poral seeding allows pulse energy to build on successive passes
through the amplifier until cavity gains and losses equalize, cre-
ating 2. 1 W (82 dB gain) of 532 nm light after passing through
a lithium niobate crystal. Unlike commercial amplifier systems,
ized and stay unaffected by cavity length or amplifier gain. Fi-
nally, the laser-diode-based configuration can produce adjust-
able pulsewidths through the addition of multiple seed diodes
coupled into low-cost fiber optic combiners. Contact Demetrios
Poulios at poulios@american.edu.
continued on page 12
continued on page 12
5000 4000 3000 2000 1000 0
103
Wavenumber (cm- 1)
Power
(a.u.)
b)
102
101
100
103
Power
(a.u.)
a)
102
101
100