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High-harmonic generation in isolated atoms and molecules has been widely utilized in extreme ultraviolet photonics and attosecond pulse metrology. Recently, high-harmonic generation has been observed in solids, which could lead to important applications such as all-optical methods to image valance charge density and reconstruct electronic band structures, as well as compact extreme ultraviolet light sources. So far these studies are confined to crystalline solids; therefore, decoupling the respective roles of long-range periodicity and high density has been challenging. Here we report the observation of high-harmonic generation from amorphous fused silica. We decouple the role of long-range periodicity by comparing harmonics generated from fused silica and crystalline quartz, which contain the same atomic constituents but differ in long-range periodicity. Our results advance current understanding of the strong-field processes leading to high-harmonic generation in solids with implications for the development of robust and compact extreme ultraviolet light sources. [ABSTRACT FROM AUTHOR]

The motion of electrons in the microcosm occurs on a time scale set by the atomic unit of time--24 attoseconds. Attosecond pulses at photon energies corresponding to the fundamental absorption edges of matter, which lie in the soft X-ray regime above 200 eV, permit the probing of electronic excitation, chemical state, and atomic structure. Here we demonstrate a soft X-ray pulse duration of 53 as and single pulse streaking reaching the carbon K-absorption edge (284 eV) by utilizing intense two-cycle driving pulses near 1.8-μm center wavelength. Such pulses permit studies of electron dynamics in live biological samples and next-generation electronic materials such as diamond. [ABSTRACT FROM AUTHOR]

High harmonics generated using the polarization gating technique are simulated under the strong-field approximation for the cases of equal and unequal ratios between the amplitudes of the two counter-rotating pulses. The effect of the field asymmetry is observed on the high harmonic yield and cut-off in the frequency domain and on the attosecond pulse duration and satellite peak contrast in the time domain. The case where the strong pulse comes later is more favourable in terms of generating a higher cut-off and a shorter pulse duration. It is predicted that thin metal filters can reduce the impact of satellite pulses while simultaneously reducing the pulse duration. [ABSTRACT FROM AUTHOR]

We implement the polarization gating (PG) technique with a two-cycle, 1.7 μm driving field to generate an attosecond supercontinuum extending to the water window spectral region. The ellipticity dependence of the high harmonic yield over a photon energy range much broader than previous work is measured and compared with a semi-classical model. When PG is applied, the carrier-envelope phase (CEP) is swept to study its influence on the continuum generation. PG with one-cycle (5.7 fs) and two-cycle (11.3 fs) delay are tested, and both give continuous spectra spanning from 50 to 450 eV under certain CEP values, strongly indicating the generation of isolated attosecond pulses in the water window region. [ABSTRACT FROM AUTHOR]

The temporal resolution of a 40 mm diameter chevron microchannel plate (MCP) detector followed by a constant fraction discriminator and a time-to-digital converter was determined by using the third order harmonic of 25 fs Ti:sapphire laser pulses. The resolution was found to deteriorate from 200 to 300 ps as the total voltage applied on the two MCPs increased from 1600 to 2000 V. This was likely due to a partial saturation of the MCP and/or the constant fraction discriminator working with signals beyond its optimum range of pulse width and shape. [ABSTRACT FROM AUTHOR]

The article presents a fast carrier-envelope phase (CEP) probe method for active control of carrier-envelope phase of a low-repetition rate, high-power chirped-pulse amplifier laser system. It states a sampling of a one kilohertz beam is taken before the hollow-core fiber and after the front-end compressor to acquire the fast CEP probe beam. It comments on the isolation of attosecond pulse production using two Brewster-angled silicon plates and a thin aluminum filter to separate the pulse.

We report a feedback control scheme that minimizes the energy fluctuations of high power femtosecond pulses from a 1 kHz laser amplifier. The pulse energy variation in the frequency bandwidth 0–500 Hz was obtained by a photodiode and a low pass filter. The measured signal was fed to a proportional-integral-derivative (differential) (PID) controller that changed the amplitude of the high voltage pulses applied to a Pockels cell. The variation of average power was reduced from 1.33% RMS to 0.28% RMS, which improved the carrier-envelope phase stability from 500 mrad to 200 mrad as measured by two f-to-2f interferometers. The long term stability of the laser was kept to approximately 0.5% RMS. [ABSTRACT FROM AUTHOR]

The creation of periodic micro/nanostructures on a variety of cutting tool materials using a femtosecond laser is reported in this paper. The materials include four types of common cutting tool materials: high speed steel (HSS), tungsten carbide (WC), silicon nitride (Si3N4), and polycrystalline cubic boron nitride (PCBN). The femtosecond laser is a Ti:sapphire laser that has a pulse width of 25 fs, a wavelength of 790 nm, and a repetition rate of 1 kHz. The femtosecond laser micromachining experiments were conducted at normal atmospheric pressure. The main operating parameters include laser fluence, polarization and cutting speed. SEM examinations reveal that ripple patterns are generated on HSS and WC. The average period of the ripples is approximately equal to the laser wavelength. The ripples are oriented perpendicular to the electric field vector of the laser irradiation. The orientation of the ripples can be controlled by changing the polarization state of the laser beam. Surface scratches can also influence ripple orientation. Nano dot matrix was created using a circularly polarized beam. However, ripple structures were not found on Si3N4 and PCBN under the same conditions. This brings in the possibility of material composition and property playing a role in the formation of the ripples. Potential applications of the micro/nanostructures on cutting tools are suggested. [ABSTRACT FROM AUTHOR]

Previously a two-color field was combined with a polarization gating to allow for the generation of single isolated attosecond pulses from multicycle lasers. Here, the scaling of energy for the extreme ultraviolet pulses corresponding to single attosecond pulses as a function of input laser pulse duration was investigated for argon, neon, and helium gas. Laser pulses as long as 12 fs were able to generate extreme ultraviolet supercontinua with high photon flux. The spectra profile depended strongly on the carrier envelope phase of the pump laser. [ABSTRACT FROM AUTHOR]

Previously, we demonstrated the stabilization of the carrier-envelope (CE) phase of the laser pulses from a chirped pulse amplifier by controlling the effective grating separation in the stretcher. In this work, we show that the CE phase can also be stabilized to ∼230 mrad by controlling the grating separation in a compressor. The cutoff frequency of the piezoelectric transducer mounted grating for the phase stabilization system was found to be higher than 60 Hz. [ABSTRACT FROM AUTHOR]

Previously, a second harmonic field was added to a polarization gating field by a Mach–Zehnder interferometer to gate the high harmonic generation process in argon gas. To reduce the losses of the interferometer, we developed a collinear setup consisting of only two quartz plates and a barium borate crystal. The high intensity at the focus allowed the double optical gating to be performed on neon gas. As a result, a supercontinuous spectrum was produced capable of supporting 130 as. There is no delay jitter between the second harmonic field and the polarization gating field associated in this setup, which is necessary for generating stable single isolated attosecond pulses. [ABSTRACT FROM AUTHOR]

The factors that limit the temporal resolution in a streak camera operating in an accumulative mode were studied. By controlling the timing jitter, the transit-time dispersion and the technical resolution of the camera on the order of 100 fs, the role of the deflection dispersion was investigated experimentally. It was done by changing the electron beam size in the deflection plates with a variable slit in front of the plates. The temporal resolution of the camera reached 280 fs when the slit width was a 5 μm slit. [ABSTRACT FROM AUTHOR]

As a compact and burgeoning alternative to synchrotron radiation and free-electron lasers, high harmonic generation (HHG) has proven its superiority in static and time-resolved extreme ultraviolet spectroscopy for the past two decades and has recently gained many interests and successes in generating soft x-ray emissions covering the biologically important water window spectral region. Unlike synchrotron and free-electron sources, which suffer from relatively long pulse width or large time jitter, soft x-ray sources from HHG could offer attosecond time resolution and be synchronized with their driving field to investigate time-resolved near edge absorption spectroscopy, which could reveal rich structural and dynamical information of the interrogated samples. In this paper, we review recent progresses on generating and characterizing attosecond light sources in the water window region. We show our development of an energetic, two-cycle, carrier-envelope phase stable laser source at 1.7 μm and our achievement in producing a 53 as soft x-ray pulse covering the carbon K-edge in the water window. Such source paves the ways for the next generation x-ray spectroscopy with unprecedented temporal resolution. [ABSTRACT FROM AUTHOR]

Investigates high voltage fast ramp pulse generators using an avalanche transistor based pulser. Applications of the device; Information on the output voltage ranges and repetition rate of the equipment; Details on the trig jitter and delay of the instrument.