Beijing Leading Online Co.,Limited

Q-switched laser

2012-07-18 07:58:14

A Q-switched laser (quality-switched laser) is a laser that emits short, high power pulses; Q-switching, also known as giant pulse formation, allows a laser to produce a pulsed beam of light. The technique produces light pulses with very high power -- much higher than would be produced by the same laser operating in a constant output (continuous wave) mode.
Compared to other techniques for pulse generation with lasers, Q-switching allows lower pulse repetition rates, higher pulse energies, and longer pulse durations. Thanks to these
differences, Q-Switched lasers have become recognized largely as the gold standard for most laser tattoo removal because they more effectively break up the ink into particles which can then be eliminated by the patient’s own immune system.
Due to their use of selective photothermolysis, Q-switched and other pulsed lasers are also useful for laser hair removal and the removal/reduction of hyperpigmentation, as well as for vascular lesions such as cosmetically undesirable broken blood vessels, spider nevi, and hemangiomas
The general equations describing Q-switched laser operation are transcendental in nature and require numerical solutions, which greatly complicates the optimization of real devices. Here, it is shown that, using the mathematical technique of Lagrange multipliers, one can derive simple analytic expressions for all of the key parameters of the optimally coupled laser, i.e. one which uses an optimum reflector to obtain maximum laser efficiency for a given pump level. These parameters can all be expressed as functions of a single dimensionless variable z, defined as the ratio of the unsaturated small-signal gain to the dissipative (nonuseful) optical loss, multiplied by a few simple constants. Laser design tradeoff studies and performance projections can be accomplished quickly with the help of several graphs and a simple hand calculator. Sample calculations for a high-grain Nd:YAG and a low-gain alexandrite laser are presented as illustrations of the technique.
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