Acousto-optic Q-switch0 pages

Sintec Optronics Pte Ltd

Sintec Optronics Technology Pte Ltd
10 Bukit Batok Crescent #07-02 The Spire Singapore 658079
Tel: +65 63167112 Fax: +65 63167113

Acousto-Optical Q-switch
The acousto-optical Q-switch often used in the laser marking makes use of mutual interaction
between an ultrasonic wave and a light beam in a scattering medium. The light beam that enters in
a direction forming a Bragg angle to the wave surface of the acoustic wave in the scattering
medium is diffracted in accordance with periodic changes in the diffraction rate produced by the
acoustic wave.
The situation is briefly explained.
First of all, an RF signal is
impressed to the transducer
adhered to the molten quartz
and
thickness
extensional
vibration is produced. Ultrasonic
shear waves are caused to
advance in the molten quartz by
this vibration, and phase grating
formed by acoustic waves is
produced. The laser beam is
diffracted when it satisfies the
Bragg angle with respect to this phase grating, and is separated in space from the incident light.
If the laser optical resonator is constructed against 0-dimensional diffracted light (undiffracted light),
the diffracted light deviates from the laser optical resonator axis when a RF signal is impressed. As
a result, loss occurs in the laser optical resonator and laser oscillation is suppressed. To make use
of this phenomenon, an RF signal is impressed for a certain length of time only (status of low Qvalue) to suspend laser oscillation. In the meantime, the population inversion of the Nd:YAG rod is
accumulated by continuous pumping. When the RF signal is reduced to zero (status of high Qvalue) and the loss to the laser optical resonator is removed, the accumulated energy is activated
as laser oscillation in a pulse form within an extremely short length of time. They are Q-switch
pulses.
This situation is briefly explained.
When an RF signal is subjected to
pulse modulation, it is possible to
periodically take out a Q-switch
pulse. When the period of Q-switch
pulses becomes shorter than the life
(about 200 μs) of the higher order of
the Nd:YAG rod, however, the
population inversion decreases and
the peak value of Q-switch pulses
decreases.

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