Double-pass imaging pulse-stretcher

Apparatus for extending the duration of an optical pulse comprising:

• an optical delay loop, said optical delay loop being in the form of a unit magnification, relay-imaging optical system and having an optical axis and a delay time;
• a beam dividing arrangement located within said optical delay loop, said beam dividing arrangement arranged cooperative with said delay loop to divide an optical pulse incident on the beam dividing arrangement along an input path into a first temporal sequence of replicas of the optical pulse, each thereof having about the same beam dimensions, a first of which is transmitted by the beamsplitter out of said delay loop and the remainder of which are reflected by the beamsplitter out of said delay loop along a first common path with the transmitted replica;
• an optical arrangement for directing said first temporal sequence of pulses back into the delay loop along a second common path laterally displaced from said first common path, said beam dividing arrangement dividing said first temporal sequence of pulses into a second temporal sequence of pulse replicas, each thereof having about the same beam dimensions, a first of which is transmitted by the beamsplitter out of said delay loop and the remainder of which are reflected by the beamsplitter out of said delay loop and each thereof propagating along a common output path, laterally displaced from said input path to form a finally-stretched pulse having a longer duration and a lower peak power than the optical pulse, said finally stretched pulse characterized as having a sequence of power peaks spaced apart in time by about said delay time;
• and
• wherein said beam dividing arrangement is arranged such that a first and second occurring of said power peaks have about equal power.

Apparatus for extending the duration of an optical pulse comprising:

• an optical delay loop, said optical delay loop including a plurality of mirrors at least some of which are focusing mirrors to provide an imaging optical system and having an optical axis;
• a beam divider for transmitting a first portion of the optical pulse and reflecting the remaining portion of the pulse into the delay loop, said delay loop being configured to return the reflected pulse back the beam divider wherein a portion of the once delayed pulse will be reflected out of the delay loop along a path common with the first portion of the pulse and a portion of the once delayed pulse will be transmitted back into the delay loop;
• and
• a reflector element positioned to receive the first portion of the optical pulse transmitted by the beam divider and the delayed pulse portions reflected from the beam divider and for redirecting received pulses along a laterally displaced path back to said beam divider and wherein said beam divider transmits a portion of the pulses received along that displaced path to define the output of the apparatus and reflecting a second portion of those pulses back into the delay loop, said delay loop being configured to return the reflected second portions of the pulses back to the beam divider wherein a portion thereof is reflected to contribute to the output of the apparatus and a portion is transmitted, with the output of the apparatus defining a finally-stretched output pulse having a longer duration and a lower peak power than the optical pulse.