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Professor David Guerra Laser  Studies

I have developed several exercises to provide an introduction laser dynamics to all levels of students. 

For high school and junior high students the most appropriate exercises are described in:
 "The Human Laser." D. Guerra, The Physics Teacher, Vol. 34, March 1996.

Figure 1: This arrangement of students describes the conditions just before the pump is turned on and the laser ions are excited.

Figure 2: This is the the laser pulse as it leaks out of the output coupler.  The time [t(rt)] is the round trip time for a photon in the laser cavity.

The Study most appropriate for college level students is:
"An Introduction to Laser Modeling Studies with a Nitrogen-pumped Dye Laser", D. Guerra, M. Morgan, and D. Coyle, The American Journal of Physics, Vol. 67 (9), pp.803-810, 1999.

The Basis for the study are the laser rate equations which can be visualized with the diagram below.

Figure 1: Energy level diagram of a four-level laser material after the pump has been turned on and stimulated emission has begun. Level 0 is the ground state, level 1 is the lower laser level, level 2 is the upper laser level, and level 3 is the pump band. The circle made of a dotted line indicates a molecule that has jumped between levels 2 and 1 during the stimulated emission of a photon.

The experiment that is used in this study is depicted in the diagram below.

Figure 2: The experimental arrangement used to measure the laser pulses is comprimised of: (a) an oscilloscope, (b) a nitrogen laser, (c) a dye laser, (d) a photodiode, (e) an index card, and (f) an aperture.

Examples of the data from the study are given in the two diagram below.

Figure 3: Oscilloscope traces of the pulses produced by the dye laser operated at a series of wavelengths under the gain curve. The pulses are labeled such that the wavelength at which the laser was operated to produce each pulse is denoted by : (a) 573 nm, (b) 576 nm, (c) 579 NM, (d) 582 NM The smallest time scale division for these traces is 1 ns.

Figure 4: Oscilloscope traces of the pulses produced by the dye laser operated at 582 nm with a series of microscope slides inserted into the laser cavity. The number below the pulse indicates the number of microscope slides in the cavity at the time that the pulse was produced. The smallest time scale division for these traces is 1 ns.

A sample of the output from a model based on the laser rate equations is given below.  The dotted line is the gain and the solid line is the output energy.

Figure 5: A simulated laser pulse from a numerical model. The solid line represents the stimulated output energy, , and the dashed line the small signal gain The large time scale divisions are 10 ns and the amplitude is in arbitrary units

The following article can be helpful to fill in some details.
"An Interactive Model of Diode-Pumped, Q-Switched / Cavity Dumped Lasers." B. Coyle, D. Guerra, and R. Kay, J. Phys. D: Applied Physics, 28, 452, 1995