As shown above, our Melles-Griot He-Ne laser consisted of a glass vacuum tube filled with approximately a ten to one mix of helium and neon gasses. The first mirror for the laser is in the end of the tube closest to the bottom of the picture, and the second mirror is outside of the tube (seen as a black square just past the tube with a small red dot in the middle). This external mirror allows us to change the length of the laser cavity.
A brass mount (custom made by Dr. Wolfgang Christian) was used to insert a microscope slide cover slip into the cavity between the tube and the external mirror. This slip was adjusted to Brewster's angle in order to polarize the beam.
Next to the laser tube on the board is the transformer that powers the laser, providing a potential difference of roughly 2000 Volts across the tube.
To focus the beam into the Spectrum Analyzer (described below) we used a 20x microscope objective. This objective screwed to a 10x microscope eyepiece was used to widen the beam and project it onto a sheet of paper in order to display the mode patterns.
To obtain data on the frequency separation between modes we used a Burleigh Spectrum Analyzer System (SA-200x) connected to a Tektronix digital oscilloscope. The output from the scope was connected to a computer running Windows NT Workstation through a GPIB interface and recorded using LabView. LabView data was exported to MS Excel and graphed using Origin.
To verify that our laser was emitting the normally expected wavelength for a red He-Ne laser we used a Burleigh Wavemeter Jr. This machine required a day of adjusting, including an expedition into the inside of the case to realign the optics.
