Tuning the Laser
From Physics 111-Lab Wiki
All pages in this lab
I. Nonlinear Spectroscopy and Magneto-Optics
II. LabView Program Descriptions
III. Photodiode Circuit and Photodiode Data Sheet
IV. Tuning the Laser
How to tune the laser
Before manually tuning the laser (which is done with the tuning knob on the back of the laser box (see Fig. 1 of the laser owner's manual), set the laser wavelength display to the appropriate USER mode. Refer to pp. 20-21 of the laser manual. Bring up the CAL menu and make sure that the USER mode is selected, then press the WAVELENGTH knob.
- Are you SURE you need to re-tune the laser? If the WAVELENGTH reading is 780.2 nm
0.4 nm, then the laser is likely already tuned. Look for other possible problems first, as the tuning procedure may take a while.
On the Diode scan program, set values for a scan which has an average voltage of 0 (e.g., Vmin= -1 and 2 Vpp), and press Start ONCE. (This will only set the values, but won't actually do a scan.) The reason for doing this is that even though the program is not scanning, it is still applying the average voltage to the servo-lock. We want it to be applying 0V to the servo-lock while we do this adjustment so that it will give us the widest range later. The Servo can only take in and put out a finite voltage range. On the Servo-lock, turn the "meter select" knob to "output", and turn the bias knob until the display reads zero. This eliminates any output offset.
Turn the tuning knob on the laser until the wavelength reading is near 780.2nm. (It will flicker back and forth about 0.2nm, which is normal) Now, while using the night vision camera, VERY SLOWLY turn the tuning knob until you see some light beams flicker in the 87/85 cell. Due to the behavior of the laser, this may only happen if you pass the point in one direction, but not the other. Since this knob is such a course adjustment, the flicker means you went through all the peaks really quickly. Try to leave the knob on a position so that you can see a constant glow in the tube. It doesn't matter which peak you are on, but some are brighter than others.
