Patent ID: 7567594

Claim:
A Q-switched laser comprising: a) a resonant cavity, containing therein a gain medium; b) a pump source for increasing an optical gain within the gain medium to produce a primary optical circulating power at a fundamental optical frequency with a cavity round trip time within the resonant cavity; c) a signal generator producing a gate signal having a gate width, and modulated at a pulse repetition frequency; d) an optical switch within the resonant cavity, responsive to the gate signal received from the signal generator to change the optical switch from a high loss state to a low loss state for a duration of the gate width for producing a primary optical pulse with a primary optical pulse width; wherein in the high loss state, energy accumulates within the gain medium to produce an initial optical gain, while the primary optical circulating power approaches an initial optical circulating power; and wherein in the low loss state, the primary optical circulating power increases to a peak optical circulating power, thereafter decaying as the energy accumulated within the gain medium diminishes and the optical gain is depleted; e) a first nonlinear coupler within the resonant cavity for converting a portion of the primary optical circulating power into a first converted optical power at a second harmonic of the fundamental optical frequency, wherein the first converted optical power has a converted optical pulse width; wherein a nonlinear coupling level, denoted by α, defined as a coefficient of P 2 in a rate equation, T RT ⁢ ⅆ P ⅆ t = gP - α ⁢ ⁢ P 2 satisfies the relationship α gi /2<α<α gi *2, wherein α gi is defined by the relationship α gi =T RT /E sat *20, where T RT is the cavity round trip time, E sat is an effective gain saturation energy, g is optical gain, P is the optical circulating power, dP/dt is a first derivative of P with respect to time, P p is the peak optical circulating power, and P init is the initial optical circulating power; and wherein the converted optical pulse width is clipped to less than about 80% at full-width half-maximum (FWHM) of a characteristic minimum pulse width, defined as the pulse width produced in a Q-switched laser having the same parameters but in the limit of the nonlinear coupling level approaching zero; and f) an output coupler for coupling the first converted optical power out of the resonant cavity.