The laws of geometric optics are covered in detail in the introductory course in physics.  Dispersion and chromatics, wave optics, polarization, light intensity, velocity of light, spectrometry are all covered by the end of two years of physics.  If a student is interested in Photonics, it is not until they take a class dedicated to the subject, that have the chance to delve into a unique experience.  Today there exists an option for a physics department to purchase one or two complete Photonic experiment setups to demonstrate an introductory topic such as the HeNe laser and perhaps the more current development of Diode laser.  These ‘kits’ come complete with all necessary components required for the setup with detailed lab exercises to the student to assemble and perform, all within a cushioned storage case.

The first observation of laser action using a gas mixture of Helium Neon was in 1961.  Nowadays much less expensive diode lasers have been substituted for their initial applications.  One important HeNe application still used today is the laser gyroscope, for navigation of airlines and missiles.  Klinger Educational offers an open frame cavity setup that allows variation of the parameters to measure the beam profile for different cavity mirror configurations and distances (P5.8.8.5).  The laser tube is equipped with Brewster’s window on both sides allowing the study of polarization and losses.  A Littrow prism selects other wavelengths than the main laser line at 632 nm, especially the orange line at 611 nm.  With the optional bifringent tuner, four different lines can be demonstrated.  An etalon is used to obtain the single mode operation of the HeNe laser.  The very first observation of laser oscillation by a student, after successful initial adjustment, is doubtlessly an unforgettable experience for the student.

Another option is to build a diode pumped Nd:YAG laser from the ground up (P5.8.6.3). First the pump diode laser is characterized. Then the process of optical pumping and the emitted spontaneous fluorescence are analyzed spectrally and temporally by modulation and changing the wavelength of the pump laser leading to the Einstein coefficients. In a third step the laser operation is initiated by adding the second cavity mirror. The laser threshold and efficiency are determined and by modulating the pump laser diode the so called spiking effect demonstrated. By changing the length of the laser cavity, the stability criterion is verified.

Using the above setup, it then possible to introduce a KTP crystal into the laser cavity leading to a frequency doubled green (532 nm) visible output.  By swapping additional components it is possible to produce 1320 nm and the doubled visible light is red at a wavelength of 660 nm.  Q-switch can be used to trigger pulses externally.

By introducing a Photonic experiment into the advanced physics classes, many students may be inspired to pursue the fascinating world of Photonics




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