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LASER: How do I adjust the length of the laser pulse?

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Title

How do I adjust the length of the laser pulse?

Question

​How do I adjust the length of the laser pulse?

Answer

​To control the laser compression you need to actuate the compressor grating stage motor. That can be done in the following way:

 
1) Disable the laser.
 
2) Open the DW04 Newport XPS controller interface in a Konqueror browser (moc-li20-dw04)
 
3) The motor channel that corresponds to the compressor grating stage is Channel 08.
 
- Make sure the laser is disabled at this point in case something goes wrong.
 
- The motor position should already be at ’20 mm’ when you start. This is the nominal position, which corresponds to a laser pulse length of roughly 200 fs. If the motor position is at another value, it is recommended that you move it to ’20 mm’ before continuing, using a motor velocity of ‘0.5 mm/s’.
 
- If the motor is not initialized, initialize and home the motor. Home position should be at position ‘0 mm’. After homing, set the motor position to ’20 mm’ before continuing, using a motor velocity of ‘0.5 mm/s’.
 
3) Open some kind of laser monitor, e.g. an experimental profile monitor that views the laser when it’s enabled. You will watch this monitor while you actuate the compressor gratings to check whether any steering (if there is any) is within the tolerance of your experimental needs.
 
4) Before enabling laser, be sure you understand the peak laser power tolerance of your experimental setup and everywhere else the laser might go! To guarantee safety of everyone’s experimental equipment, do not operate at a compression of less than ~200 fs unless you have explicit permission from system experts.
 
5) Enable the laser and observe it on your monitor, noting the starting position.
 
6) Actuate the grating motor to the desired position/compression. Watch the laser monitor to ensure steering (if there is any) is within the tolerance of your experimental needs as you move the gratings. Move the gratings at a velocity of ‘0.5 mm/s’. Approximate compression table listed below:
 
(Based on calculation from Philippe Hering: 1ps/28mm)
 
Motor Position - Pulse Length
0 mm - 989 fs
5 mm - 810 fs
10 mm - 417 fs
15 mm - 453 fs
20 mm - 274 fs
22 mm - 203 fs
[YOU MUST HAVE EXPLICIT PERMISSION FROM SYSTEM EXPERTS TO EXCEED THIS LEVEL OF COMPRESSION!]
25 mm - 95.7 fs
26 mm - 60 fs
 
7) Once you have reached your desired compression, use the laser for your experiment at will!
 
8) After you have completed your experiment, return the grating motor position to ’20 mm’ at a velocity of ‘0.5 mm/s’.
 

Attachments

Version: 1.0
Created at 5/26/2014 5:03 PM by Clarke, Christine
Last modified at 5/26/2014 5:03 PM by Clarke, Christine

SLAC SLAC National Accelerator Laboratory, Menlo Park, CA
Operated by Stanford University for the U.S. Dept. of Energy