Tsunami - Beckman Institute Laser Resource Center

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Pulse Width Measurement
The Spectra-Physics Lasers 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 displayed on a high impedance oscilloscope, providing the
user with instantaneous 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 scanning time base is calibrated by moving a calibration
etalon of known thickness 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 rotating blocks, it can be used to measure pulse
widths from 25 ps to c 80 fs.
HRRl
1
I
'
Calibration
HRR2 Rotating
Block 1 I
(Thin Block Shown)
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t
Alignment
Beam Splitter
~ - - - - - Input - ~
I
i Beam I Alignment
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Splitter
I Iris
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t
1 t I
1 I
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& Lens
PMT UV
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5 F r r X i l I
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M3
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Alignment
Target
M
HRR
Xtal
PMT
Mirror
Hollow Retro-reflector
Non-linear Crystal
Photomultiplier Tube
- Figure B-3: The Model 409 -08 Autocorrelator Optical Path. The beam paths are displaced by
HRRl and HRR2 in and out of the plane of the paper, so the configuration corresponds to the
background-free method shown in Figure B-2.