Patent ID: 7692854

Claim:
A regenerative amplifier for amplifying a seed pulse in response to an external trigger-signal, comprising: a source of seed pulses; a primary resonator terminated by first and second mirrors and arranged to receive the seed pulses, the primary resonator including a gain-medium and an optical switch, said optical switch operable to selectively close the primary resonator to trap therein a seed pulse from the source and to open the primary resonator to deliver the seed pulse therefrom after the seed pulse has been amplified in the primary resonator; a pump radiation source arranged to optically pump the gain-medium in a continuous-pumping mode thereby providing available gain in the gain-medium; a secondary resonator including the gain-medium, the secondary resonator not including the optical switch, but including a selectively-variable attenuator for selectively varying losses in the secondary resonator; and wherein in the optical switching arrangement and the selectively-variable attenuator are controllable such that when the gain-medium is being pumped and the seed pulse is not being amplified the selectively-variable attenuator allows lasing to occur in the secondary resonator at a level selected to limit gain in the gain-medium to a predetermined level, and wherein upon receipt of a trigger signal, the selectively-variable attenuator causes lasing to cease in the secondary resonator for a predetermined time period during which gain in the gain medium is allowed to rise above the predetermined level, the optical switching causes the seed pulse to be trapped in the primary resonator and the trapped seed pulse is amplified in the primary resonator, and such that after the predetermined time period the optical switch causes the amplified seed pulse to be delivered from the secondary resonator, and the selectively-variable attenuator again allows lasing to occur in the secondary resonator at the level selected to limit gain in the gain-medium to the predetermined level.