FAQ: Laser (10 TW Ti:Sapph)
Question:
What is the laser in question?
Answer:
The laser system is coarsely divided up into two parts: the Sector 20 Research Laser, which comprises the kHz front end of the laser system, the FACET Ionization Laser, which includes the 10Hz preamplifier and main amplifier. The Sector 20 Research Laser includes an RF locked oscillator, a Ti:Sa Regen, a YLF pump laser, and a pulse cleaner/slicer. The FACET Ionization Laser consists of two 10Hz YAG pump lasers, one with a 15mm Ti:Sa crystal (preamplifier) and one with a 20mm Ti:Sa crystal (main amplifier).
Components of the complete FACET Ionization Laser System:
Coherent Legend enclosure includes the following...
68MHz oscillator w/ RF locking loop Coherent VITARA w/ SLAP optics; w/o SYNCHROLOCK
Ti:Sa Regen 1.5mJ uncompressed Coherent HE+ USP 1kHz
kHz Q-switched YLF pump laser Coherent Evolution-30
Pulse cleaner/slicer....
Coherent High Contrast Pulse Slicer
Large aperture Pockels Cell in slicer
Faraday cages on PC of slicer
FACET Ionization Laser - Preamplifier...
Ti:Sa phi8x15mm
10Hz, 13mJ flash lamp YAG pump QUANTEL CFR200
FACET Ionization Laser - Main Amplifier...
Ti:Sa phi20x20mm
10Hz, 1.6 J flash lamp YAG pump THALES SAGA Standard
The lasers are arranged on a ’U’-shaped table located in a room of the LCLS laser injector facility, just off the Klystron Gallery at Sector 20.
Question:
What is the Laser Hazard Zone in the FACET tunnel?
Answer:
The Laser Hazard Zone in the FACET tunnel extends between the laser curtains just upstream of the THz table and downstream of the IP Area.
Please see the layout here.
Question:
How do I make an emergency exit when laser is operating?
Answer:
If there is an emergency and you cannot use the sector 19 staircase, there are emergency exits at the sector 20 alcove and through to LCLS. You can pass safely through the curtains to make an emergency exit even if the laser is operational.
Opening the laser curtains shuts off the laser transport.
Passing through the curtains in Class 4 (laser operation) mode will close and disable T1/T2 transport safety shutters. There is no hazard- you are safe to proceed without eyewear.
This is part of the laser safety system. Opening the curtains disables the hazard and you can proceed to the nearest emergency exit.
Question:
How do I pass through the curtains when it isn't an emergency?
Answer:
If you need to pass through the curtains and the laser is operational, there is a rotating red light on. If there is no red light, the laser is off. You can open the curtains and proceed as usual.
If the rotating red light is on, it means the laser is operational and people are actively working on it. It is courteous to contact the laser operators using the sector 20 phone (call x7486) to request an entry such that they can find an appropriate breaking place in their work.
Should you open the curtains when the laser is operational, the transport shutters close and the laser is not transported to FACET. There is no safety risk to anyone. The laser hazard is disabled and you can proceed without goggles. However, this is not helpful to the people working on the laser so we politely request that you don't do this.
Rotating Red Light OFF - no laser. Open curtains.
Rotating Red Light ON - laser in operation. Call x7486 to request entry.
When the curtain is opened, the laser hazard is disabled. There is no safety hazard when you open the laser curtains.
Question:
How do I know if the laser is operating in the FACET tunnel?
Answer:
There is a rotating red light at the ends of the Laser Hazard Zone. If it is on, the laser is operating in the tunnel. If it is off, the laser is not operating in the tunnel.
When the laser is being transported to the FACET tunnel, the curtains are closed. This prevents stray laser light from escaping the laser hazard zone. It is safe to be outside the laser hazard zone when the laser is operating.
Red light on - Laser hazard exists between the curtains.
Red light off- no laser hazard exists.
Question:
Do I need additional training just to be in the FACET tunnel?
Answer:
If the laser is not operating in the tunnel or if you never enter the laser hazard zone, no- no additional training required.
Course AD103 (FACET Tunnel Hazards) is sufficient.
There is no hazard associated with the laser if it is not getting transported to the tunnel. And if it is getting transported to the tunnel, the hazard only exists in the laser hazard area.
But what if you need to be in the laser hazard zone when the laser is operating? Generally speaking this is never the case! The only people who need to be in the laser hazard zone are qualified laser operators.
If you think you ought to be a qualified laser operator, discuss this with your supervisor and the SLSO (Brendan O'Shea).
Question:
What training do I need to work with the laser?
Answer:
See the Training FAQ.
Question:
How do I enable/disable the laser remotely?
Answer:
Here is how you enable or disable the FACET Laser from EPICS (turns on/off pump triggers)
1) Open FACET Home screen. From there...
2) Click on "Laser" / "LI20" button.
3) Click on "Change Laser Output State" button.
4) Click on button in red box. Says "Disabled" when laser is disabled, "Enabled" when laser is enabled.
Question:
How do I adjust laser timing?
Answer:
Here is how you operate the FACET Laser Timing Controls:
1) Open FACET Home screen. From there...
2) Click on "Laser" / "LI20" button.
3) Make sure the "Locked" box and the "Frequency Counter" and "Measured Phase Offset" numbers are all green and not red. If any of them are red, call Mike Litos, or Joe Frisch, or Justin May.
4) Click on "Vitara" button.
5) Make sure all the display boxes are green (or blue) and not red. For now, you can ignore "FS Python Script Status" (which is red). If any of the other display boxes have red text, call Mike Litos, or Joe Frisch, or Justin May.
6) Make sure "Auto On/Off" in the "Automatic Operation" area is set to "Automatic" and is blue. If not, call Mike Litos, or Joe Frisch, or Justin May.
7) Make sure "PID Mode" in the "Vitara Coarse Motor PID on Piezo V" area is set to "On" and is blue. If not, call Mike Litos, or Joe Frisch, or Justin May.
8) Make sure the "Target Freq" in the "Manual Frequency Search" area is set to 67999964 [Hz] (i.e. just shy of 68 MHz) and is blue. If not, call Mike Litos, or Joe Frisch, or Justin May.
9) Make sure the "RF Lock Enable" in the "RF Locking" area is set to "Enabled" and is blue. If not, call Mike Litos, or Joe Frisch, or Justin May.
10) Look at the "Target Time" box and the "Counter Time" box inside the "RF Locking" area. If these numbers do not agree to within 0.2ns, call Mike Litos, or Joe Frisch, or Justin May.
10) Finally, adjust the timing of the laser by manually entering a value in the "Target Time" box in units of ns inside the "RF Locking" area. For now, it should be somewhere in the vicinity of 535ns to match the e-beam arrival time. You can change this value over a scale of 100 ns all the way down to 1 fs, though the laser is likely to be stable only to ~50 fs, in reality. After you change the "Target Time" value, give the laser a few seconds to settle on the new time. For jumps at the >1 ns scale, wait 5 seconds or so. For jumps at the <1 ns scale, wait 2 or 3 seconds. You can watch the "Counter Time" monitor just below the "Target Time" box to see the actual live laser timing down to <ns scale. Note that right now there is a known problem where the noise on this monitor is on the scale of 100ps. This noise is only on the monitor device; it is not the actual laser timing jitter.
Short Version:
Laser On/Off: FACET Home -> Laser/LI20 -> Change Laser Output State -> Enable/Disable Button
Laser Timing: FACET Home -> Laser/LI20 -> Vitara -> Target Time; make sure everything is
green :)
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’.
