Spectrally combining lasers could unleash the potential of laser-plasma accelerators

A group of researchers from the Accelerator Expertise & Utilized Physics (ATAP) Division at Berkeley Lab has developed a brand new approach for combining fiber lasers working at completely different wavelengths to provide ultrashort laser pulses. The analysis was revealed within the journal Optics Specific.

The work might advance the event of laser-plasma accelerators (LPAs), which have the potential to push the frontiers of high-energy physics and allow discoveries in supplies science, fusion analysis, and plenty of different areas.

LPAs use intense, ultrafast laser pulses passing by means of a plasma to speed up charged particles as much as a thousand instances quicker than present applied sciences. They promise extra compact and highly effective machines which are cheaper to construct and function than standard accelerators.

Presently, most LPAs use laser pulses with repetition charges of only some Hertz (Hz); nonetheless, realizing the total potential of LPAs “would require high-power laser techniques able to producing ultrashort, high-energy laser pulses at repetition charges within the kHz vary or greater,” says Siyun Chen, a Analysis Scientist at ATAP’s BELLA Middle, who led the experimental demonstration of the brand new approach.

These constraints, provides Chen, place very demanding necessities on the laser techniques that generate such pulses. So, the researchers turned to fiber lasers, which she says are the “best high-power laser expertise demonstrated up to now and still have in depth industrial growth that might be leveraged in our work.”

Though the vitality and energy of pulses produced by fiber lasers will be scaled up by combining a number of pulses in area (spatially) and in time (temporally), these pulses, nonetheless, are presently restricted to a couple of hundred femtoseconds (fs), which aren't brief sufficient to drive LPAs.

“Whereas fiber laser techniques supply the best wall-plug efficiencies—the electrical-to-optical energy effectivity—the spectrum of ultrashort laser pulses amplified in these techniques narrows,” explains Tong Zhou, a Analysis Scientist in ATAP’s BELLA Middle who led the event of the brand new approach.

“This achieve narrowing is a basic impact when laser pulses are amplified on this manner; the narrower the heartbeat’s spectrum is, the longer its period. Consequently, it is rather difficult for high-power fiber lasers to generate pulses shorter than a couple of hundred fs.”

Nonetheless, by spectrally combining a number of laser pulses working at adjoining wavelength ranges, the group, which additionally included Qiang Du from the Engineering Division and Dan Wang and Russell Wilcox from ATAP, achieved an ultra-broad mixed spectrum in a position to assist very brief pulses at tens of fs.

To extend the bandwidth and produce tens-of-fs-long pulses, the researchers first used a mode-locked oscillator and ytterbium-doped fiber amplifier (YDFA) to generate pulses of 120 fs at 100 MHz repetition charges. These have been despatched to a photonic-crystal fiber, the place their spectrum was broadened from 27 nanometers (nm) to 90 nm.

They then used a dichroic mirror, which permits laser pulses to be separated or mixed with out considerable depth loss, to separate the heartbeat spectrally. These have been then despatched to 2 pulse shapers to form the depth and section of the respective pulse spectra. Whereas the mirrored pulses have been despatched to the primary shaper, the transmitted pulses have been amplified by the YDFA, pulse-shaped by the second shaper, and additional break up by one other dichroic mirror. The three chirped pulses from the fiber laser have been then amplified and recombined utilizing further dichroic mirrors.

“This ultra-broadband spectral combining with synthesized pulse shaping produced pulses of solely 42 fs in period, which is considerably shorter than the pulses generated from every of the three fiber channels,” says Chen. “We consider that is the shortest pulse period ever achieved from a spectrally mixed ytterbium fiber laser system.”

Zhou notes, “Whereas the work has demonstrated ultrafast pulses which are to this point at low vitality, it demonstrates the important thing ideas of ultra-broadband spectral combining and coherently spectrally synthesized pulse shaping and offers a path ahead for utilizing fiber lasers to drive LPAs.”

The group plans so as to add extra amplification levels and implement multidimensional strategies able to spatially, temporally, and spectrally combining fiber lasers to provide high-energy, tens-of-fs laser pulses.

Commenting on the work, ATAP Division Director Cameron Geddes says, “It exhibits how researchers at ATAP are driving the event of superior particle accelerators that promise discoveries in basic scientific analysis and breakthroughs in fusion, medication, materials science, and plenty of different areas.”