Page 349 - High Power Laser Handbook

318 So l i d - S t at e La s e r s Ultrafast Solid-State Lasers 319

Input

Beam splitter
Delay line
Lens

BBO

Oscilloscope
Detector

Figure 12.14 Autocorrelation setup.

technique, pioneered by Dan Kane and Rick Trebino, allows both
the shape and phase of the pulse to be retrieved; in addition, this
method will indicate whether the measurement is being done prop-
37
erly. In this new method, which is called frequency resolved opti-
cal gating (FROG), the autocorrelator setup basically stays the
same, while the detector is replaced with a spectrometer, so that a
spectrum can be taken at each time delay. From this, a two-dimen-
sional spectrogram is measured; this spectrogram carries all the
amplitude and phase information. A simple algorithm is applied to
the data to retrieve the pulse shape, temporal phase, spectrum, and
spectral phase.
Other methods have since been developed that make the mea-
surement faster and easier. On the FROG side, the GRENOUILLE
(Swamp Optics, Inc.) is a real-time device that displays the spectro-
38
gram and the retrieved information. Another device, called a Scan
FROG, uses the standard Mach-Zehnder interferometer in addition
to a voice coil to perform the time delay very quickly and an algo-
rithm that can update at ~2 Hz. Another widely used method is the
Spectral Phase Interferometry for Direct Electric-field Reconstruc-
39
tion (SPIDER). Many other techniques may be found for a wide
variety of wavelengths, from the extreme ultraviolet to the midin-
frared.