Chih-Hsuan Lu

Generation of intense supercontinuum in condensed media

Generation of supercontinuum in condensed media is a well-known approach to expand the spectrum of a femtosecond laser pulse. Yet large material dispersion and low optical damage threshold have limited input pulse energy to a few microjoules, making solids unattractive for high power applications [1]. Here we report the use of a multiple plates system that overcomes these problems to generate an intense supercontinuum (MPContinuum) that contains several hundred microjoules of energy and preserves the advantages of being compact, simple to operate, and highly reproducible [2]. With this multiple plates approach, we have obtained pulses that have an octave-spanning spectrum that covers from 450 nm to ~980 nm at the −20 dB intensity level while converting as much as 62 % of the input pulse energy to the MPContinuum. Frequency-resolved optical gating and spectral interferometric measurements indicate that the pulse is phase coherent so that it is compressible to a few femtoseconds.

Generation of octave-spanning supercontinuum by Raman-assisted four-wave mixing in single-crystal diamond

An octave-spanning coherent supercontinuum is generated by non-collinear Raman-assisted four-wave mixing in single-crystal diamond using 7.7 fs laser pulses that have been chirped to about 420 fs in duration. The use of ultrabroad bandwidth pulses as input results in substantial overlap of the generated spectrum of the anti-Stokes sidebands, creating a phase-locked supercontinuum when all the sidebands are combined to overlap in time and space. The overall bandwidth of the generated supercontinuum is sufficient to support its compression to isolated few-to-single cycle attosecond transients. The significant spectral overlap of adjacent anti-Stokes sidebands allows the utilization of straight-forward spectral interferometry to test the relative phase coherence of the anti-Stokes outputs and is demonstrated here for two adjacent pairs of sidebands. The method can subsequently be employed to set the relative phase of the sidebands for pulse compression and for the synthesis of arbitrary field transients.

Generation and characterization of isolated, circularly polarized, attosecond pulses

We experimentally demonstrate angularly and temporally isolated counter-rotating circularly polarized attosecond pulses at 33 eV. The pulse contrast and circular polarization of the beams are fully characterized by a field autocorrelator and an EUV polarimeter.

Generation of octave-spanning intense supercontinuum from Yb:Doped solid-state lasers in multiple thin plates

Most few-cycle pulses are formed by compression of an ultrabroadband light source obtained in meter-long hollow-core fiber filled with noble gas [1]. However, the hollow-core fiber scheme requires a careful alignment and is extremely sensitive to the beam-pointing direction, limiting its long-term stability. Recently we reported a novel approach of using a set of plates for continuum generation (MPC, schematic is shown in fig. 1(a)) using 800 nm 28 fs pulses [2]. In this paper, we present a MPC generation scheme for driving with 1030 nm lasers that have pulse duration of as long as 170 fs. We demonstrate a spectrum spanning from 550 nm to 1250 nm, (bandwidth at −20 dB intensity) that is capable of supporting single-cycle pulses while maintaining good output beam quality.

Intense coherent supercontinuum via IR pulse propagation in multiple thin plates

We report on the coherent supercontinuum produced by ultra-fast IR pulses propagating through thin plates. The −20 dB supercontinuum spans from 750 to 1650 nm and has a total energy of 100 uJ.

Raman-assisted octave-spanning continuum generation in single-crystal diamond for sub-cycle pulse synthesis

A coherent continuum is generated by Raman-assisted four-wave mixing in single-crystal diamond of an 8 fs laser pulse. The bandwidth of the spectrum will support the synthesis of an isolated single-cycle femtosecond pulse.