Table of Contents
Day 2 Pt. 1 - Record a calibration spectrum
Before placing your group table on the main optical table, check that both the alignment laser beam and the IR laser beam pass through the centers of the two irises. You will have to use the video camera to observe the location of the IR beam on the two irises. Chances are the IR beam will be good and the alignment laser will be off. You should at least attempt to realign the alignment laser beam before asking for one of the lab staff to do it. Realigning the IR laser however should be done by one of the lab staff.
Before beginning temperature measurements, you should obtain a calibration spectrum using the interferometer. This may require some slight adjustments to the optics on the Interferometer half of you group table. It is easiest to do this before you put the wedge beam splitter back in place for the doppler broadened measurement.
Once you have aligned the interferometer and obtained a clean interference pattern on the scope, use the cursor feature of the scope to measure the locations of the interference maxima (including an estimate on the uncertainty of these measured values) and record them in your lab notebook. You should also transfer a screenshot and the digitized data to the lab computer for inclusion in your out of lab assignment.
You will be expected to be able to articulate clearly and concisely how you performed this measurement, and how you estimated the uncertainties in the measured values.
Do not forget to measure and record the dimensions of the interferometer.
Day 2 Pt. 2 - Restore Day 1 Setup
Refer to the Figure below while performing the following steps.
- After recording your calibration spectra, block the beam entering the Interferometer half of your group board so that unwanted reflections do not make it into the spectroscopy optics.
- Put the wedge beamsplitter back in its post holder and realign the pump beam to pass through the vaporcell and into photodetector III. You can refer back to the Day 1 instructions if needed.
- Once you have the Probe Beam reestablished, carefully place the heated vaporcell with Helmholtz coils on your group board so that the Probe Beam passes cleanly through the vaporcell.
- Note that this vaporcell is recessed within the insulation and coils so that it is difficult to see. But it is easy to simply slide it back and forth until the Probe Beam clearly makes it through.
Day 2 Pt. 3 - Measure the FWHM of the db absorption peak for one transition as a function of temperature.
Today you will perform a more in depth investigation of the temperature dependence of the thermal doppler broadening effect.
On day one you measured the FWHM of the doppler broadened absorption peak for one of the Rb D1 emission lines as part of the initial setup and optical alignment. Now you will measure the FWHM of the same doppler broadened peak as a function of temperature, up to 50ºC.
Instructions for adjusting the temperature of the vapor cell can be found here
Instead of using the stand alone vaporcell you will use the vaporcell and Helmholtz coil apparatus which includes a built in temperature controller. Once you have reinstalled your small optical bench on the main bench, carefully place the larger vaporcell assembly on the table so that both beams from the wedge beam splitter pass through and into the photodetectors. You will notice that for this instrument the vaporcell is imbedded deep within the heater and coil assemblies making it more difficult to observe directly where the guide laser beams are striking it. It is not however too difficult to tell when both beams are passing cleanly through the vasporcell by looking for the to spots at the photodetectors. A piece of foam core board can help with locating them.
Once you have the vaporcell in place, switch to the IR laser and tune it onto resonance as you did on Day 1. On the scope obtain a stable trace that passes cleanly through all of the absorption features.
There are instructions in the lab for how to adjust the temperature of the vaporcell, which can be set to temperatures up to 50ºC.
On the scope zoom in on the same doppler broadened peak you used on Day 1. The procedure now is very straight forward. Starting with the vaporcell at room temperature, approximately 20ºC, use the scope to measure the FWHM of the doppler broadened peak for ~5 temperatures up to 50ºC. For each measurement you will need to;
- Adjust the temperature setpoint on the controller,
- wait for the temperature of the vaporcell to come to equilibrium,
- capture the absorption profile of the peak on the scope,
- transfer the digitized waveform to the lab computer,
- and measure the FWHM using the scope cursors.
Do not forget to estimate the uncertainties in your measured quantities.
This procedure should not take more than a couple hours. Once you are finished, return the vaporcell to its default temperature of 50ºC.