Pulse picking laser

A method of changing the repetition rate of a mode locked oscillator comprising:

• a) directing a seed beam having a preselected polarization from said mode locked laser on a seed beam path;
• b) passing said preselected polarization beam through a thin film polarizer transmissive for said preselected polarization to remove polarized beam having a polarization other than said preselected polarization;
• d) directing beam transmitted from said thin film polarizer through a Faraday rotator and a half wave plate to rotate the preselected polarization by 90° degrees;
• e) focusing said beam propagating from said Faraday Rotator and half wave plate to a preselected spot size;
• f) directing the focused beam into an AOM to incident on said AOM at a preselected location on said AOM such that the beam is separated into zero order beam and a first order first pass beam with a preselected beam separation;
• g) reflecting said first order first pass beam back to said AOM;
• h) focusing said reflected first order first pass beam to a preselected spot size prior to it incidenting on said AOM;
• i) said focused and reflected first order first pass beam incidenting on said AOM at about the same preselected location as said seed beam such that said first order first pass beam is separated into zero order beam and a first order second pass beam with a preselected beam separation;
• said first order second pass beam traveling on the same path as said seed beam only in the opposite direction;
• j) collimating said second pass first order beam;
• k) directing said collimated beam through a Faraday rotator and a half wave plate said polarization of said beam remaining rotated 90° to said preselected polarization;
• l) directing said second pass first order beam from the Faraday rotator and half wave plate to a polarizer reflective to said rotated polarization to extract said polarization rotated second pass first order beam as the output beam.