Main PageEO Modulators
See the experiment in Chapter 4 in which the gain of a Q-Switched ruby laser is determined by using an EO modulator as a variable loss. Unlike AO modulators, EO modulators may be used as a variable loss (i.e. they may be turned partially on) with insertion loss predicted by equation 7.5.5.
AO Modulators
Chapter 7 is concerned with fast pulse production of which Q-switching is the primary technique. Most Q-switched lasers (e.g. YAGs) use acousto-optic modulators similar to the one outlined here.
The particular AO modulator outlined here uses a Tellurium oxide crystal operating at a fundamental frequency of 80MHz. Unlike the one in the book, this unit is designed as a modulator rather than a Q-switch - although it could very well be used a Q-switch.
Shown here operating, the Raman-Nath diffraction pattern is clearly identifiable with the first and second order pattern visible.
A lab experiment cenetered around this AO modulator in which students investigate Raman-Nath and Bragg diffraction as well as extinction ratios under each regime.
Practical Q-Switches
This practical Q-switch from a YAG laser, shown below in an experimental test setup, requires a much higher drive power than smaller modulators - this is logical given the size of the element. Here an amateur laser transmitter with a rated output power of 50W of RF power is used to drive the switch. An antenna tuner is used to match the output impedance of the transmitter to that of the switch. Impedance of the system must be matched properly to ensure that RF energy is delivered to the piezoelectric element in the switch. The photo above details the insides of the switch which includes water-cooling tubes.
The diffraction pattern produced resembles that in the text with multiple orders visible. Te arrangement above allows the switch to be characterized with respect to required drive power and sensitivity to the frequency of the RF energy employed.