Pulse Width Measurement
B-3
The Spectra-Physics Model 409-08 scanning autocorrelator operates in a
background-free configuration according to the principles of noncollinear
autocorrelation. It allows the autocorrelator signal to be conveniently dis-
played on a high impedance oscilloscope, providing the user with instanta-
neous feedback of laser performance. The optical path of the Model 409-08
is shown in Figure B-3. The Model 409-08 uses a rotating block of fused
silica for varying the relative path lengths of both beam paths, and the scan-
ning time base is calibrated by moving a calibration etalon of known thick-
ness in and out of one of the beam paths. The Model 409-08 can be used
over the wavelength range from 650 to 1600 nm and, by changing the rotat-
ing blocks, it can be used to measure pulse widths from 25 ps to < 80 fs.
Figure B-3: The Model 409-08 Autocorrelator Optical Path. The beam paths are displaced by
HRR
1
and HRR
2
in and out of the plane of the paper, so the configuration corresponds to the
background-free method shown in Figure B-2.
Input
Alignment
Iris
Alignment
Beam Splitter
Alignment
Target
M
2
M
1
HRR
1
HRR
2
Rotating
Block
(Thin Block Shown)
Xtal
UV
Filter
PMT
M
3
Lens
Main
Beam
Splitter
Calibration
Etalon
M
HRR
Xtal
PMT
Mirror
Hollow Retro-reflector
Non-linear Crystal
Photomultiplier Tube
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