Regenerative amplifiers utilizing chirped pulse amplification (CPA) have been the dominant means for obtaining pulse energies greater than a microjoule with pulse durations in the femtosecond to picosecond range. Microjoule to millijoule pulse energies with pulse durations below 10 picoseconds have been found to be particularly useful for micromachining and for medical applications such as Lasik. However, a big stumbling block in the utilization of ultrafast sources for these applications has been that the regenerative amplifier is more of a piece of laboratory equipment and not conducive to the industrial setting.
Alternative sources for microjoule level, ultrafast pulses are emerging; utilizing all fiber chirped pulse amplification designs. Such systems are inherently more stable since they are based on technology similar to that utilized in Telecomm systems. During the past decade, there has been intensive work and success in making such systems practical. However, for higher pulse energies in the millijoule range, regenerative amplifiers will continue to dominate for some time since pulse energies above a millijoule have not been demonstrated in an all fiber system.
For micromachining applications, more industrially compatible regenerative amplifiers are now being developed based on Nd: or Yb: doped materials, rather than the Ti:sapphire that has dominated the scientific market. There are two basic reasons for this change. Commercial markets typically do not require the shorter pulses that can only be obtained from the Ti:sapphire regenerative amplifier, and the Nd: and Yb: based materials can be directly diode pumped, which makes these systems more robust and less expensive. An unresolved technical issue for Nd: or Yb: based regenerative amplifiers is the need for an equally robust seed source for femtosecond or picosecond pulses. The present seed lasers are mode-locked solid-state lasers with questionable reliability. It would be preferable to have a robust fiber seed source similar to that which has been developed for the Ti:sapphire regenerative amplifier, and used where Ti:sapphire regenerative amplifiers are applied to more commercial applications.
In a copending U.S. application Ser. No. 10/960,923, filed which is assigned to the common assignee and the disclosure of which is incorporated by reference in its entirety, the design changes needed for a mode-locked Yb:doped fiber oscillator and amplifier to be utilized as a seed source for a Yb: or Nd: based solid-state regenerative amplifier are described. The purpose of this application is to modify and apply many of the improvements in all fiber chirped pulse amplification systems for application to the seed source of a regenerative amplifier.