Abstract
We report the results of theoretical and experimental studies on passive spatiotemporal shaping of cw mode-locked picosecond laser pulses for driving the photocathode of a high-brightness, high-current energy recovery linear accelerator. The temporal pulse shape is modified using birefringent crystals, while a refractive optical system is used to generate a flattop spatial beam profile. An optical transport system is designed and implemented to deliver the flattop pulse onto a photocathode sited 9 m away from the shapers. The alignment tolerances on the beam shaper and the temporal pulse stacker have been studied both theoretically and experimentally. The experimental results agree well with theoretical simulations.
Highlights
Shaping the spatial and the temporal profiles of ultrashort pulse laser beams is highly desirable for several scientific research and industrial applications, such as producing low-emittance photoelectrons for accelerators [1,2,3], high-harmonic generation [4], optical parametric amplifiers [5], laser micromachining [6], and terahertz generation [7]
We begin by describing the underlying physical principle of the birefringent-crystal-based passive pulse stacker, and we present our theoretical calculation to determine the temporal profile of the shaped laser pulse
The beam expander can be positioned either before or after the temporal pulse shaper, we found that the latter configuration was best for assuring high-quality spatiotemporal shaping
Summary
Shaping the spatial (transverse) and the temporal (longitudinal) profiles of ultrashort pulse laser beams is highly desirable for several scientific research and industrial applications, such as producing low-emittance photoelectrons for accelerators [1,2,3], high-harmonic generation [4], optical parametric amplifiers [5], laser micromachining [6], and terahertz generation [7]. The high-current ERL being built at Brookhaven National Laboratory [3] requires flattop transverse and longitudinal profile with pulse duration of $60 ps for low charge ( < 1:4 nC) and $120 ps for high charge ( > 5 nC) operations. Longer duration (nanosecond) laser pulses can be directly shaped by an electro-optic modulator [15,16].
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