Laser Focus World - September 2013

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.