Generation of millijoule-level sub-5 fs violet laser pulses

We demonstrate the generation,spectral broadening and post-compression of second harmonic pulses using a thin beta barium borate(BBO)crystal on a fused-silica substrate as the nonlinear interaction medium.By combining second harmonic generation in the BBO crystal with self-phase modulation in the fused-silica substrate,we efficiently generate millijoule-level broadband violet pulses from a single optical component.The second harmonic spectrum covers a range from long wave ultraviolet(down to 310 nm)to visible(up to 550 nm)with a bandwidth of 65 nm.Subsequently,we compress the second harmonic beam to a duration of 4.8 fs with a pulse energy of 0.64 mJ(5 fs with a pulse energy of 1.05 mJ)using chirped mirrors.The all-solid free-space apparatus is compact,robust and pulse energy scalable,making it highly advantageous for generating intense second harmonic pulses from near-infrared femtosecond lasers in the sub-5 fs regime.

Hyper spectral resolution stimulated Raman spectroscopy with amplified fs pulse bursts

We present a novel approach for Stimulated Raman Scattering(SRS)spectroscopy in which a hyper spectral resolution and high-speed spectral acquisition are achieved by employing amplified offset-phase controlled fs-pulse bursts.We investigate the method by solving the coupled non-linear Schrödinger equations and validate it by numerically characterizing SRS in molecular nitrogen as a model compound.The spectral resolution of the method is found to be determined by the inverse product of the number of pulses in the burst and the intraburst pulse separation.The SRS spectrum is obtained through a motion-free scanning of the offset phase that results in a sweep of the Raman-shift frequency.Due to high spectral resolution and fast motion-free scanning the technique is beneficial for a number SRS-based applications such as gas sensing and chemical analysis.

Rapid-Scan Nonlinear Time-Resolved Spectroscopy over Arbitrary Delay Intervals

Femtosecond dual-comb lasers have revolutionized linear Fourier-domain spectroscopy by offering a rapid motion-free,precise,and accurate measurement mode with easy registration of the combs beat note in the radio frequency domain.Extensions of this technique already found application for nonlinear time-resolved spectroscopy within the energy limit available from sources operating at the full oscillator repetition rate.Here,we present a technique based on time filtering of femtosecond frequency combs by pulse gating in a laser amplifier.This gives the required boost to the pulse energy and provides the flexibility to engineer pairs of arbitrarily delayed wavelength-tunable pulses for pump-probe techniques.Using a dual-channel millijoule amplifier,we demonstrate programmable generation of both extremely short,fs,and extremely long(>ns)interpulse delays.A predetermined arbitrarily chosen interpulse delay can be directly realized in each successive amplifier shot,eliminating the massive waiting time required to alter the delay setting by means of an optomechanical line or an asynchronous scan of 2 free-running oscillators.We confirm the versatility of this delay generation method by measuringχ(2)cross-correlation andχ(3)multicomponent population recovery kinetics.