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The measurement and control of light field oscillations enable the study of ultrafast phenomena on sub-cycle time scales. Electro-optic sampling (EOS) is a powerful field characterization approach, in terms of both sensitivity and dynamic range, but it has not reached beyond infrared frequencies. Here, we show the synthesis of a sub-cycle infrared-visible pulse and subsequent complete electric field characterization using EOS. The sampled bandwidth spans from 700 nm to 2700 nm (428 to 110 THz). Tailored electric-field waveforms are generated with a two-channel field synthesizer in the infrared-visible range, with a full-width at half-maximum duration as short as 3.8 fs at a central wavelength of 1.7 µm (176 THz). EOS detection of the complete bandwidth of these waveforms extends it into the visible spectral range. To demonstrate the power of our approach, we use the sub-cycle transients to inject carriers in a thin quartz sample for nonlinear photoconductive field sampling with sub-femtosecond resolution.

It has been demonstrated in the past that high fluxes of extreme ultraviolet (XUV) light could be obtained by driving high harmonic generation (HHG) with high energy lasers. However, the peak intensity at the focal point of a femtosecond laser with more than 100 mJ can be too high for phase-matched HHG in gases. We propose a method to optimize the spatial profile at off-focus locations of the high energy driving laser to avoid fully ionizing the target atoms. The beam profile before or after the focal point depends on the wavefront quality of the laser beam and the near field intensity distribution. The beam spot diameter reaches three times that at the focus by adding customized wavefront terms. An XUV pulse energy of 5.6 μJ was obtained from HHG when a larger off-focus spot of a 500 mJ Ti: sapphire laser beam was applied in an argon gas cell.

We developed and implemented an experimental setup for the generation of high-energy high-order harmonics in argon gas for nonlinear experiments in the extreme ultraviolet (XUV) spectral range. High-order harmonics were generated by loosely focusing a high-energy laser pulse centered around 800 nm into a gas cell filled with argon in a phase-matching condition. The wavefront distortions of the driving pulse were corrected by a deformable mirror, and the XUV conversion efficiency was significantly improved due to the excellent beam profile at focus. A high-damage-threshold beam splitter was used to eliminate high-energy driving pulses co-propagating with high-order harmonics. The setup has a potential to provide intense ultrashort XUV pulses reaching the intensity levels required for nonlinear experiments in the XUV spectral range.

Abstract: Double-Pulse Laser-Induced Breakdown Spectroscopy of iron using both Nd:YAG and TEA–CO2 lasers has been investigated to better understand mechanisms of signal enhancement. The signal dependence on the delay between the two laser pulses shows an enhanced signal when the CO2 laser pulse interacts with the sample before the Nd:YAG pulse. Signal kinetics and a simple model of sample heating by the CO2 pulse show that the enhancement during the first 700ns is due primarily to sample heating. Images of the sample surface after ablation as well as time-integrated pictures of the plasma suggest that particles are ejected from the surface during the first microseconds after the arrival of the CO2 pulse and provide fuel for the subsequent plasma created by the Nd:YAG laser. [Copyright &y& Elsevier]

Laser-induced breakdown spectroscopy (LIBS) using double-pulse irradiation with Nd:YAG and CO(2) lasers was applied to the analysis of a polystyrene film on a silicon substrate. An enhanced emission signal, compared to single-pulse LIBS using a Nd:YAG laser, was observed from atomic carbon, as well as enhanced molecular emission from C(2) and CN. This double-pulse technique was further applied to 2,4,6-trinitrotoluene residues, and enhanced LIBS signals for both atomic carbon and molecular CN emission were observed; however, no molecular C(2) emission was detected.