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Pumping of Solid State Lasers with FELs

High average-power free-electron lasers may be useful for pumping high peak-power solid-state laser-amplifiers. At very high peak-powers, the pump source for solid-state lasers is non-trivial: flash lamps produce thermal problems and are unsuitable for materials with short florescence-times, while diodes can be expensive and are only available at select wavelengths. FELs can provide pulse trains of light tuned to a laser material’s absorption peak, and florescence lifetime. An FEL pump can thus minimize thermal effects and potentially allow for new laser materials to be used.

Table: A comparison of existing laser pump sources with the FEL based pump. The FEL is suited to high energy and short wavelength applications.

Pump Source
Flashlamp
Diode
Laser
FEL
Avg. Energy
Very high
High
Low
High
Peak Energy
Medium
Low
High
Very High
Heat Load
High
Low
Low
Very Low
Wavelength
VIS
IR - NIR
IR-UV
IR - UV

An Example

We envision an FEL driven by the front end of the LCLS including the photoinjector, low-energy linac and bunch compressor. The photoinjector is assumed to have a high quantum-efficiency cathode and be driven by a multi-pulse laser (e.g. LANL AFEL or the DESY TTF). The resultant beam parameters are assumed to be 2000 bunches (filling every 5th RF bucket) each of 1 nC. At the end of the first bunch compressor (BC-1), the beam is 250 MeV with a peak current of 500 A. Such a beam, sent into an FEL with 5% efficiency can deliver 25 J of pump light (at 490 nm) over the fluorescence time of Ti:S (about 3.5 µs).

Figure: A schematic of the front end of the LCLS with a multibunch beam diverted into a seeded FEL acting as a pump for a Ti:S amplifier.

Such a system could deliver over 100TW out of a Ti:S amplifier.

Table: Study parameters for a 100TW 800nm laser pumped by an FEL on LCLS

Parameter Value
Pump Wavelength [Ti:S] 490 nm
Macrobunch Length [Ti:S] 3.5 µs
Macrobunch Energy 500 J
Microbunches 2000
(1 in 5 RF buckets)
Beam Energy [LCLS] 250 MeV
Peak Current [LCLS] 500 A
Undulator Period 5 cm
Undulator Parameter 2.5
Undulator length
(Un-optimized; depends on seed) &Mac197; 20 m
FEL efficiency 5%
Optical energy per pulse 12.5 mJ

Additional Information

G. Travish, J. K. Crane and A. Tremaine, Free-Electron Lasers as Pumps for High-Energy Solid-State Lasers, submitted for publication: Proc. FEL 2003 [PDF].