We demonstrate a compact 20 Hz repetition-rate mid-IR OPCPA system operating at a central wavelength of 3900 nm with the tail-to-tail spectrum extending over 600 nm and delivering 8 mJ pulses that are compressed to 83 fs (<7 optical cycles). Because of the long optical period (∼13 fs) and a high peak power, the system opens a range of unprecedented opportunities for tabletop ultrafast science and is particularly attractive as a driver for a highly efficient generation of ultrafast coherent x-ray continua for biomolecular and element specific imaging.

90 GW peak power few-cycle mid-infrared pulses from an optical parametric amplifier

The generation of extremely short isolated attosecond pulses requires both a broad spectral bandwidth and control of the spectral phase. Rapid progress has been made in both aspects, leading to the generation of light pulses as short as 67 as in 2012, and broadband attosecond continua covering a wide range of extreme ultraviolet and soft X-ray wavelengths. Such pulses have been successfully applied in photoelectron and photoion spectroscopy and recently developed attosecond transient absorption spectroscopy to study electron dynamics in matter. In this Review, we discuss significant recent advances in the generation, characterization and applications of ultrabroadband, isolated attosecond pulses with spectral bandwidths comparable to the central frequency. These pulses can in principle be compressed to a single optical cycle. This review discusses significant recent advances in the generation, characterization and application of ultrabroadband isolated attosecond pulses with a spectral bandwidth comparable to the central frequency, which can in principle be compressed to a single optical cycle.

The generation, characterization and applications of broadband isolated attosecond pulses

Over the last decade, control of atomic-scale electronic motion by non-perturbative optical fields has broken tremendous new ground with the advent of phase-controlled high-energy few-cycle pulse sources1. The development of close to single-cycle, carrier-envelope phase controlled, high-energy optical pulses has already led to isolated attosecond EUV pulse generation2, expanding ultrafast spectroscopy to attosecond resolution1. However, further investigation and control of these physical processes requires sub-cycle waveform shaping, which has not been achievable to date. Here, we present a light source, using coherent wavelength multiplexing, that enables sub-cycle waveform shaping with a two-octave-spanning spectrum and a pulse energy of 15 µJ. It offers full phase control and allows generation of any optical waveform supported by the amplified spectrum. Both energy and bandwidth scale linearly with the number of sub-modules, so the peak power scales quadratically. The demonstrated system is the prototype of a class of novel optical tools for attosecond control of strong-field physics experiments. Researchers present a waveform synthesis scheme that coherently multiplexes the outputs from two broadband optical parametric chirped-pulse amplifiers. The technique provides control at the sub-cycle scale and generates high-energy ultrashort waveforms for use in strong-field physics experiments.

/pdf/high-energy-pulse-synthesis-with-sub-cycle-waveform-control-2lgl1w9idz.pdf

High-energy pulse synthesis with sub-cycle waveform control for strong-field physics

High-harmonic spectroscopy probes atomic structure by looking at the short-wavelength emission excited from atoms by ultrafast pulses of laser light. It is now shown that this technique can even detect signatures of electron–electron interactions.

/pdf/probing-collective-multi-electron-dynamics-in-xenon-with-1s8pe2nwea.pdf

Probing collective multi-electron dynamics in xenon with high-harmonic spectroscopy

This is a review of some recent development in femtosecond filamentation science with emphasis on our collective work. Previously reviewed work in the field will not be discussed. We thus start with a very brief description of the fundamental physics of single filamentation of powerful femtosecond laser pulses in air. Intensity clamping is emphasized. One consequence is that the peak intensity inside one or more filaments would not increase significantly even if one focuses the pulse at very high peak power even up to the peta-watt level. Another is that the clamped intensity is independent of pressure. One interesting outcome of the high intensity inside a filament is filament fusion which comes from the nonlinear change of index of refraction inside the filament leading to cross beam focusing. Because of the high intensity inside the filament, one can envisage nonlinear phenomena taking place inside a filament such as a new type of Raman red shift and the generation of very broad band supercontinuum into the infrared through four-wave-mixing. This is what we call by filamentation nonlinear optics. It includes also terahertz generation from inside the filament. The latter is discussed separately because of its special importance to those working in the field of safety and security in recent years. When the filamenting pulse is linearly polarized, the isotropic nature of air becomes birefringent both electronically (instantaneous) and through molecular wave packet rotation and revival (delayed). Such birefringence is discussed in detailed. Because, in principle, a filament can be projected to a long distance in air, applications to pollution measurement as well as other atmospheric science could be earned out. We call this filamentation atmospheric science. Thus, the following subjects are discussed briefly, namely, lightning control, rain making, remote measurement of electric field, microwave guidance and remote sensing of pollutants. A discussion on the higher order Kerr effect on the physics of filamentation is also given. This is a new hot subject of current debate. This review ends on giving our view of the prospect of progress of this field of filamentation in the future. We believe it hinges upon the development of the laser technology based upon the physical understanding of filamentation and on the reduction in price of the laser system.

Advances in intense femtosecond laser filamentation in air

We demonstrate a four-stage optical parametric chirped-pulse amplification system that delivers carrier-envelope phase-stable approximately 1.5 microm pulses with energies up to 12.5 mJ before recompression. The system is based on a fusion of femtosecond diode-pumped solid-state Yb technology and a picosecond 100 mJ Nd:YAG pump laser. Pulses with 62 nm bandwidth are recompressed to a 74.4 fs duration close to the transform limit. To show the way toward a terawatt-peak-power single-cycle IR source, we demonstrate self-compression of 2.2 mJ pulses down to 19.8 fs duration in a single filament in argon with a 1.5 mJ output energy and 66% energy throughput.

/pdf/self-compression-of-millijoule-1-5-microm-pulses-1is9g977zf.pdf

Self-compression of millijoule 1.5 microm pulses.

Carrier-envelope phase-stable 4 μJ pulses at ~1.5 μm are obtained from a femtosecond Yb:KGW-MOPA-pumped two-stage optical parametric amplifier. This novel technology represents a highly attractive alternative to traditional Ti:sapphire front-ends for seeding multimillijoule-level optical parametric chirped-pulse amplifiers. For this task, we demonstrate stretching of the OPA output to ~40 ps and recompression to 33 fs pulse duration. As a stand-alone system, our tunable two-stage OPA might find numerous applications in time-resolved spectroscopy and micromachining.

Scalable Yb-MOPA-driven carrier-envelope phase-stable few-cycle parametric amplifier at 1.5 μm

The terahertz time-domain spectroscopy system using 1030 nm wavelength femtosecond pulses generated by a Yb:KGW laser is presented. The system, employing p-InAs crystal as the emitter and GaBiAs dipole antenna as the detector, has reached the spectral width of more than 2 THz and the signal-to-noise power ratio of ∼60 dB.

Terahertz time-domain spectroscopy system based on femtosecond Yb:KGW laser

Single 4-mJ supercontinuum filaments supporting 8-fs pulses are generated by focusing ultrashort pulses from a four-stage KTP-OPCPA into a noble-gas cell. The use of a 1.6-µm wavelength permits efficient energy scaling in the single-filament regime.

Infrared multimillijoule single-filament supercontinuum generation

We demonstrate a four-stage optical parametric chirped-pulse amplification system that delivers carrier-envelope phasestable
~1.5 μm pulses with energies up to 12.5 mJ before recompression. The system is based on a fusion of
femtosecond diode-pumped solid-state Yb technology and a picosecond 100 mJ Nd:YAG pump laser. Pulses with 62 nm
bandwidth are recompressed to a 74.4 fs duration close to the transform limit. To show the way toward a terawatt-peakpower
single-cycle IR source, we demonstrate self-compression of 2.2 mJ pulses down to 19.8 fs duration in a single
filament in argon with a 1.5 mJ output energy and 66% energy throughput.

/pdf/efficient-4-fold-self-compression-of-1-5-mj-infrared-pulses-4qvxexqgsj.pdf

J. Pocius

Papers

Self-compression of millijoule 1.5 microm pulses.

Scalable Yb-MOPA-driven carrier-envelope phase-stable few-cycle parametric amplifier at 1.5 μm

Terahertz time-domain spectroscopy system based on femtosecond Yb:KGW laser

Infrared multimillijoule single-filament supercontinuum generation

Efficient 4-Fold Self-Compression of 1.5-mJ Infrared Pulses to 19.8 fs