Optical amplifier with two seed source lasers controlled to reduce stimulated Brillouin scattering

Apparatus for providing optical radiation, which apparatus comprises:

• a first seed source for providing first seeding radiation comprising pulses;
• a second seed source for providing second seeding radiation comprising pulses;
• the first seed source is a Fabry Perot semiconductor laser, and the second seed source is a Fabry Perot semiconductor laser;
• a coupler connected to the first seed source and the second seed source for coupling the first seeding radiation and the second seeding radiation together;
• at least one amplifier for amplifying the first seeding radiation and the second seeding radiation;
• a controller for controlling the first seed source, the second seed source, and the amplifier;
• the controller controls the first seed source and the second seed source via laser diode drivers such that pulses from the first seed source and the second seed source overlay each other;
• the first seeding radiation is characterized by a first wavelength, the second seeding radiation is characterized by a second wavelength, and the first wavelength is the same as the second wavelength;
• the controller controls the first seed source, the second seed source and the amplifier to amplify the first seeding radiation and the second seeding radiation with the amplifier such that the pulses have higher peak powers, higher average powers, and higher pulse energies than for a similar apparatus that does not include the second seed source, the apparatus being such that it is possible to control the first seed source the second seed source, and the amplifier such that random spikes superimposed on backward travelling pulses that propagate in an opposite direction to the optical pulses increase in frequency and amplitude when a peak power of the second seeding radiation is reduced;
• and
• such that a peak power of the first seeding radiation is greater than a threshold peak power that results in stimulated Brillouin scattering of sufficient intensity to damage the apparatus when there is no second seeding radiation emitted by the second seed source and to prevent a peak power of the second seeding radiation reducing to a level at which the apparatus exceeds a damage threshold of the apparatus, whereby the apparatus is operable to provide the optical radiation with a peak power that is greater than when there is no second seed source.