Lasers

In the lab rooms we use several lasers between 780nm and 860nm (NIR). These lasers are pumped by Coherent's Verdi laser shreding green light and can be monitored with their respective driver. Below we give an exhausitve explanation of the procedure you must follow between the moment you arrive un the lab room and the beginning of your experiments

Turn on pump lasers.

1. Turn the key on the "on" position and wait until the current seeking displayed on the screen of the pump laser controller stabilize around a value.
2. Press the button power level 1. The power value displayed on the screen of the controller represent the optical power the laser should provide. You can change it by turning the potentiometer on the controller. Depending on the laser you're using (V10 or V18) make sure this power setting does not exceed the maximum output power of the laser.
3. Press the buton "shutter" to open the shutter. Now you should see green laser light outcoming the cavity.

Turn off/Standby pump lasers.

1. Make sure the power value displayed on the controler screen is not set to his maximum value. In this case, lower the power at least 2W under the maximum value.
2. Press the button power level 1 to stop the cavity from lasing.
3. Close the shutter.
4. Wait for the current displayed on the screen to decrease and stabilize and then turn the key on the "standby" position.
5. Usually we let it in standby mode from one use to the other. If you want to turn it off completely, go in the menu and press the option "cool the vanadate".
6. Wait untill the vandate temperature decrease from its high value to a the room temperature (a fast cooling of the vanadate could break the nonlinear crystal for the frequency doubling)

Monitoring the lasers

To get the best performance of your laser you must make sure it is properly aligned. To do so, use a powermeter at the laser output and maximise the optical power by using the appropriate mirrors screws.

A laser properly aligned should provide your the best optical output power and stability both in intensity and frequency. Each laser of the lab room has is own driver that you need to turn on if you want to monitor your laser.

Chiller

Any laser in the lab room is water-cooled by a chiller. If the cooling is not properly done the laser can stop working and eventually break. As a consequence you must make sure there is always dry-water in the chiller. Usually we refill it every week/two weeks. If you see a water leak coming out from the chiller immediately turn the laser off and fix the leak (enjoy).

Polariton room specifities

Lasers

Matisse : monitored localy from the computer with the software Matisse Commander
M2 : monitored through internet by entering the IP adress 192.168.1.213 in the searching bar (works only if your laptop is on the sub-network of the lab room)

Spectrometer

In the polariton lab room we use gratings spectrometer to make dispersion measurments. The principle scheme is presented just below.

For a good use of the spectrometer the most important point is to make the Fourier Transform of your beam at the entry of the spectrometer exactly where the slit is located (a). Then the two parabolic mirrors inside the spectometer (b) and (d) make the image of the reciprocal space on the output camera. As you can see on the scheme, a diffraction grating (c) is placed in between the mirrors in order to spatially separate the photons of differents energies. This final grating can be changed to get different dispersive capacitiese. The smaller is the grating step the more it is dispersive.

Optical alignment

To use the whole sensor of the output camera you should use the right lense to match the numerical aperture of the spectrometer.

Softwares

To monitor the spectrometer (change the grating, center energy) we use mainly two softwares : Lightfield and Winspec (WInspec is an old version of Lightfiled) Lightfield

The software is easy to use. Still, knowing some features will make you win a great amount of time. When you export a data from Lightfield, you can choose many options :

1. Which is the unity off your axis (nm or eV)
2. Which is the format you want your file be exported into.

The basic setting export you the files in the format .spe which is a format made specially by Princeton Instruments. To open and treat a SPE file your can use the library ***.

Another option is to export your file into .csv format which is convenient for treatment because the data are storred in a dictionnary.

WARNINGS

Open-flow cryostat cooling procedure

1. Pumping of the cryostat
   1. Open the inlet valve of the cryostat
   2. Launch the Pascal vacuum pump: the pressure should reach ~ 5x10^-2 mbar
   3. Launch the turbo pump (0 -> 25000 rpm): final pressure ~ 9x10^-4 mbar
      Do not launch the turbo pump if the vacuum is greater than 5x10^-2
2. Injection of the transfer cane into the dewar
   1. Close the dewar outlet valve
   2. Connect the Jussieu input to the tranfer cane
   3. Put the transfer cane on the dewar entrance
   4. Tighten the joint in order to lock the transfer cane
      The transfer cane doesn't must fall too fast inside the dewar
   5. Open the dewar inlet valve
   6. Let the transfer cane slides gently against the joint, adjust the tightening to change its speed
      The transfer cane speed must be regular to not create ice that would block the circulation
   7. The dewar pressure MUST increase to 0.5 mbar in order to initiate the helium flow inside the cryostat
      Do not let the pressure exceed 0.5 mbar, open the outlet valve to decrease it
   8. Reach the bottom of the dewar
3. Connection to the cryostat
   1. Insert the cold finger of the transfer cane inside the cryostat
   2. Launch the motorized circulation and open the flow regulation valve to its maximum
   3. Slightly raise the transfer cane in the dewar
      Adjust the dewar position to reduce the pressure in the cryostats if it is greater than 3x10^-3mbar
      The cryostat temperature should fall to 3.8K in 5 minutes
4. Self-sustained helium circulation
   Useful to eliminate the vibrations due to the motorized circulation. The pressure in the dewar should be at least equal to 4mbar in order to feed the helium circulation
   1. Once the temperature in the cryostat is stabilized, switch off the motorized circulation
   2. Wait again for the temperature stabilization
   3. Close progressively the regulation valve until the temperature icreases again
   4. If needed, cut the Pascal pump

Open-flow cryostat warming up procedure

1. Isolate the cryostat from the Turbo pump by closing ist inlet valve
2. Open the dewar outlet valve
3. If not already done, switch off the motorized circulation
4. Wait for the temperature to reach T>120K
5. Click on the STOP button of the Turbo pump
6. Wait for 0 rpm
7. Remove the transfer cane cold finger from the cryostat
8. Remove the transfer cane from the dewar (put gloves)
9. Close the dewar inlet
10. Unconnect the Jussieu input from the transfer cane
11. Block the Jussieu input

FAQ

• The pressure in the dewar exceeds 0.5 mbar during the experiment
  1. Open the motorized circulation if closed
  2. Gently open the dewar outlet valve
  3. Let the pressure decrease to ~ 0.4 mbar
  4. Close the outlet valve
  5. Stop again the motorized circulation
• The temperature in cryostat is increasing drastically
  1. Open the motorized circulation AND the flow controller valve if closed
  2. IF the temperature decreases again, wait for T = 4K then closes the circulation again
  3. ELSE do the warming up procedure to put an end to the experiment
• One of the rubber pipe is broken
  1. Close the Jussieu valve in the Rubiroom
  2. Open the dewar manual safety valve
  3. Do the warming up procedure
• The temperature doesn't reach 4K after the cooling process
  1. You need to redo the cooling, do the warming up procedure

Close circuit cryostat

Vacuum pumping

Cooling & warming procedure

Piezo