Overview:
In the optics lab we use a He-Ne laser (0.5 mW, TEM00 mode, wavelength = 632.8 nm).
For this exercise we looked at the output of a laser which had been off for a few weeks.
Results:
The laser was mounted on the optical bench. We used a beam spreader with a magnification of 7 and an iris between the two lenses. We also could place a polarizer in the beam. The intensity was viewed with a 1 mm diameter fiber centered on the beam.
First we used a laser which had been on for some time to do an alignment. We also measured the spot size by sweeping the fiber mounted on the linear translator across the beam. The resulting data and fit to a Gaussian are shown below.
We then replaced with a laser which had been off for several weeks. In the plots shown below we show data over the same time spread (2 minutes) and voltage output spread to allow for comparisons.
This is the measurement of the output intensity starting about 30 sec after the laser was first turned on.
We then inserted a polarizer whose axis was oriented at 0o and then switched to a polarizer at 90o
The 90o is in place - laser on for a little over 5 minutes
The 90o is in place - laser on for a little over 20 minutes
