Directions for using sodium lidar
(Updated March 2012)
-Start up the seed lasers, from the IP 128. 39.135.160 for the 1064nm and 1319nm
-Turn on the standby button for the 1064nm seed
-Wait for the actual temperature to reach the set temperature for both diodes of the
1319nm seed laser
-Turn on diodes (green button) for the 1319nm laser
Standby 1064
Diode on/off
Temperature toggle
Above: Program to turn on instruments, right is the 1064 (top) and 1319 (bottom)
-Make sure that the temperature to the sum frequency generator is well adjusted to
obtain maximum power (thermistor reading here is 5.2)
Above: Power reading and temperature adjustment
-The coupling of the two seed lasers into the fiber can also be adjusted. Each
individual laser can be looked at separately to ensure that both are overlapped and
properly coupled in.
-Generally the knob pointing up and the one pointing down in the following figure
are the best ones to increase coupling
Above: Stage for coupling of seed lasers into the
fiber
Frequency Generation
Using the piezo scan program to lock the laser
-Turn on the power to the doppler free sodium cell PMT from the computer
-Start the scan piezo labview program(piezoscan5a)
-Choose the direction of scanning (left or right, red or blue)
-flip the tune switch in the program
-once the dip is seen in the screen, turn off the tune switch
-turn on piezo feedback and slow tune feedback
-turn piezo amplitude down to about .5V (do this after everything else is ready as
the lasers may continue to warm up and the lock may be lost)
An image of tuning program
note: If there is ever concern about the spectrum, the voltage divider can be
disconnected for a larger sweep range than 10V so that a larger range can be seen
by the viewer. Also, it is good to let the seed lasers warm up for a period of time
before dropping the scan voltage, this way the tuning does not get stuck in a second
dip that is not the lowest point.
-Turn on the AOM from the computer
Note: The controls for the shutter can be set to manual or, when collecting data, they
must be set to x_gate for the shutter and ttl for the AOM shutters.
Shifted Beam Alignment 1
Shifted Beam Alignment 2
AOM Control
Unshifted Beam Alignment
Shutter Control
-Turn on the PDA pumps from the computer (always do this before turning on the
yag or the cells can crack)
-check PDA power sources beneath the PDA. These should be between 10-12V and
should be checked during the time running the laser.
-Be sure that the motor is pumping the dye. This should also be checked throughout
the duration of running the laser. (Feel pumps for vibrations).
Above: Left, pump power sources. Right, PDA pumps
-Turn the key to the water cooler in the hall (to the right)
-Turn all values upward (parallel to the pipes) in the hall next to the water cooler.
Put the note on that the sodium lidar is running. The one in the middle will be
turned if the other lider is on.
-If the lidar has not been run in awhile, check the gauges in the back of the cooler to
make sure that the system is above the fill line.
Above: Valves for cooler and the water cooler with key switch at bottom right
-When first adjusting the setup after a period of time, look for the bulls eye pattern
at the output of the first and second stage of the PDA output and make sure it looks
spherical. This can be done for each shifted frequency and the non-shifted
frequency.
Look for Bulls Eye for each of
the unshifted and shifted beams
and a piece of paper. Alignment
can be done from the alignment
mirrors in the AOM control box.
Finer adjustments can be made
using a power meter.
-Turn the power on for the yag. Sometimes the simmer on the system fails, and if
this happens, just retry until it works.
-Turn on the choppers using the computer in the back. This is from IP 128.
39.135.160
-Turn on BNC delay box from the back computer
-hit run on the actual delay box (in the bottom right corner of the box)
-turn on PMTs from the computer, and turn on the high voltage from the control
boxes (yellow buttons underneath the table)
Chopper
Control
High Voltage
Buttons
BNC Delay Run Button
-Turn on the yag by choosing run_norm from the control box. The choppers and BNC
delay must be on by this point in order for the laser to externally trigger.
-It may take a bit for the yag to warm up, but the yag q_switch is started from
run_norm. If this does not start the yag, go to monitor->Beamlock on. Additionally, if
this still does not work turn d_lock on.
Above: YAG Laser control box
-Go back to the piezo scan program
-In the piezo scan program, recheck that the lowest point is still locked and lower
the sweep range to about .5V
Using The Faraday Filters
Note: for more information on how to replace the sodium cells or open the filters
see Katrina’s March 2012 trip report.
-Turn on the Faraday Filters using the control at:
http://128.39.135.107/ov.html
-The filters need to warm up for 1.5-2 hours
-Set up the faraday filters and diodes to take a spectrum of the faraday filter
transmission
-Use the test fiber and connect this to the input side of a chopper (make sure that
light is coming through the fiber first)
-Make sure that the chopper is open so that light will get through (see figure)
-Collimate the light from the fiber. One of the 25mm lenses that is attached between
the PMTs and the chopper is good for this purpose. (Katrina left the 25mm lens
attached to the Faraday Filter on the March trip)
-Attach a 50mm lens to front of the diode and attach the diode at the end of the
faraday filter
-When taking spectra, BOTH diodes must be on, even if only one filter is being used
-The piezo scan MUST be OFF in order to run the scan spectrum program
Open chopper
-Run the program to take a spectra
-The piezo scan MUST be OFF in order to run the program:
Run the program ScanandSaveSpectrum10June2010.vi
-change the name of the save file and select the save file option
-Once a spectrum has been obtained, turn on the piezo scan program again and
relock the frequency
Above: ScanandSaveSpectrum program
-Set up the receiver with the faraday filter
-Connect the fiber from the telescope of interest to the input side of the faraday filter
where the test fiber was previously connected. Replace the diode with the PMT
setup.
Note: I used the previous PMT setup (25mm, interference filter, 50mm lens) after
the faraday filter and left the other 50mm lens with the diode. This may need to be
changed to better focus the light on the PMT detector. I also left a 25mm lens at the
front of the faraday filter to collimate light coming out of the fiber.
-Chopper 1 does not have a stop plate so be careful
Above: Left, diode w/50mm lens
Right, chopper w/ 25mm lens before filter
Chopper
Faraday Filter
Input for test
fiber or receiver
telescope
Col. Lens
Either 30mm & Diode
Or
25mm/filter/50mm & PMT
Above: Faraday filter setup
Taking Data
-The conditions for taking data, in addition to clear weather, are that the winds must
be lower than 12m/s.
-Be sure to uncover the telescope that you will be using
-Make sure that the MCA servers for the counter boards are running before starting
the data acquisition program (otherwise it will not work). Go to
Programs/FastComtecP7882/MCA-3.
-Before taking data, it is good to align the system by steering the beams to align with
the telescopes. This can be done by using the DOS program on the right computer.
-The Labview program Run3FreqBiff5b.vi can be run with the save data option off.
-To make this process easier, it is possible to only send out one frequency during
this time by turning the shutter to manual and turning the AOM controls off.
-Use the DOS program at this point to adjust the motor control boxes to the left of
the computer. Remember to turn these on before starting the adjustments.
-There is a spreadsheet of relative motor adjustments for beam steering changes
between zenith and off zenith directions on the blue cabinet by the door. It can be
helpful to use these positions to adjust the mirror positions, just be sure to look at
the difference in the motor positions and use this difference to adjust the mirrors.
-Once the signal is good, the shutter should be turned to X_gate enable, and the two
AOMcontrols should be turned to ttl.
-The save data option in the program can be turned on and the group number
should be adjusted to suit the data. For instance if data was taken earlier in the day,
the group number should be changed.
-Be sure to log the data run in the log book and keep track of the time that the laser
has been used and the age of the dye.
Above: Data acquisition program
Above: stepper motor control program
Above: List of relative motor positions
Above: MCA Server
Shut Down
-Stop the data acquisition program
-Stop the tune piezo program then turn off the Doppler free detector
-If you were using the faraday filters, it may be good to take a second spectrum
-Turn off lamps to the yag
-Turn off choppers and BNC delay
-Be sure to turn off the high voltage to the PMTs in addition to turning off the PMTs
-Turn off the PDA pumps
-Shut down AOM crystals and shutters
-Turn of the seed lasers, first by hand, then using the computer
-Turn off the Doppler free detector
-Turn off the yag laser
-Turn off the power supply and water pumps