Frequency-tripled fiber mopa

Optical apparatus, comprising:

• a fiber-MOPA, the fiber MOPA including an arrangement for providing pulses of radiation having a fundamental wavelength, an arrangement for dividing the fundamental-wavelength pulses into first and second portions and directing the first and second fundamental-wavelength pulse-portions into respectively first and second output channels, and first and second fiber-amplifiers in respectively the first and second channels for amplifying respectively the first and second fundamental-wavelength pulse-portions;
• an arrangement for generating second-harmonic radiation pulses from the amplified fundamental-wavelength pulse portions from the first fiber-amplifier;
• a wavelength- and polarization-selective reflective and transmissive surface arranged to cause the second-harmonic radiation pulses and amplified second fundamental-wavelength pulse-portions from the second fiber-amplifier to propagate collinearly along a common path;
• and
• a sum-frequency generator arranged to receive the collinearly propagating second-harmonic radiation pulses and amplified second fundamental-wavelength pulse-portions and sum-frequency mix the second-harmonic radiation pulses and amplified second fundamental-wavelength pulse-portions to provide pulses of third-harmonic radiation.

Optical apparatus, comprising:

• a fiber-MOPA, the fiber MOPA including an arrangement for providing pulses of radiation having a fundamental wavelength, an arrangement for dividing the fundamental-wavelength pulses into first and second portions and directing the first and second pulse-portions into respectively first and second output channels, and first and second fiber-amplifiers in respectively the first and second channels for amplifying respectively the first and second fundamental-wavelength pulse-portions;
• an arrangement for generating second-harmonic radiation pulses from the amplified fundamental-wavelength pulse portions from the first fiber-amplifier and directing the second-harmonic radiation pulses along a first path;
• an arrangement for directing the second amplified fundamental-wavelength pulse portions along a second path at an angle to the first path;
• and
• a sum-frequency generator arranged to receive the second-harmonic radiation pulses and amplified second fundamental wavelength pulse-portions on the first and second paths and sum-frequency mix the second-harmonic radiation pulses and the amplified second fundamental wavelength pulse-portions to provide pulses of third-harmonic radiation, the angle between the first and second paths being selected to minimize Poynting vector walk-off in the sum-frequency mixing process.

A method of generating third harmonic pulses comprising the steps of:

• generating fundamental laser pulses from a fiber master oscillator;
• splitting each of the pulses between first and second propagation channels;
• amplifying the fundamental pulses in the first channel;
• frequency converting the amplified fundamental pulses in the first channel into second harmonic pulses;
• amplifying the fundamental pulses in the second channel;
• and
• sum frequency mixing the second harmonic pulses and the amplified fundamental of the second channel to generate third harmonic pulses.