High power femtosecond laser with variable repetition rate
Designs and techniques for constructing and operating femtosecond pulse lasers are provided. One example of a laser engine includes an oscillator that generates and outputs a beam of femtosecond seed pulses, a stretcher-compressor that stretches a duration of the seed pulses, and an amplifier that receives the stretched seed pulses, amplifies an amplitude of selected stretched seed pulses to create amplified stretched pulses, and outputs a laser beam of amplified stretched pulses back to the stretcher-compressor that compresses their duration and outputs a laser beam of femtosecond pulses. The amplifier includes a dispersion controller that compensates a dispersion of the amplified stretched pulses, making the repetition rate of the laser adjustable between procedures or according to the speed of scanning. The laser engine can be compact with a total optical path of less than 500 meters, and have a low number of optical elements, e.g. less than 50.
1. A method of scanning with a laser system, the method comprising:
generating femtosecond seed pulses by an oscillator;
stretching a duration of the seed pulses by a stretcher;
amplifying stretched seed pulses by an amplifier into laser pulses;
compensating a group delay dispersion of the laser pulses in the range of 5,000-20,000 fs 2 with a dispersion compensator between end-mirrors of the amplifier;
outputting the laser pulses from the amplifier by an electro-optical modulator at a first repetition rate;
compressing a duration of the laser pulses to the range of 1-1,000 fs by a compressor;
focusing the laser pulses to a focus spot in a first target region with a scanning laser delivery system;
scanning the focus spot with the first repetition rate in the first target region with the scanning laser delivery system;
changing the first repetition rate to a second repetition rate with a repetition-rate controller; and
scanning the focus spot with the second repetition rate in a second target region with the scanning laser delivery system.
2. The method of claim 1 , wherein:
the first target region is at least one of a lens region and a cataract region, and
the second target region is a corneal region.
3. The method of claim 1 , wherein:
the first target region is a corneal region, and
the second target region is at least one of a lens region and a cataract region.
4. The method of claim 1 , wherein:
the first repetition rate is less or equal to 100 kHz; and
the second repetition rate is greater than 100 kHz.
5. The method of claim 4 , wherein:
the second repetition rate is 150 kHz.
6. The method of claim 1 , wherein:
the compressor and the stretcher are integrated into a stretcher-compressor.
7. The method of claim 1 , wherein:
the electro-optical modulator includes a switchable polarizer,
configured to rotate a polarization plane of the stretched pulses in the amplifier,
the switchable polarizer having a rise time less than 5 ns.
8. The method of claim 7 , the scanning laser delivery system comprising:
a control electronics configured to apply control signals to the switchable polarizer to cause the switchable polarizer to switch with a rise time of less than 5 ns.
9. The method of claim 1 , the changing the first repetition rate to a second repetition rate comprising:
changing a number of roundtrips of laser pulses before outputting the laser pulses from the amplifier by the electro-optical modulator.
10. The method of claim 1 , the changing the first repetition rate to a second repetition rate comprising:
changing the first repetition rate to the second repetition rate in a time in the range of 1 μsec-1 sec.