Sapphire Ultrafast Laser Research Articles

A novel common-path scheme for fourth harmonic generation by ultrashort laser pulses

A new compact common-path scheme for Fourth-Harmonic Generation (FHG) of femtosecond laser pulses is proposed here. Guidelines for selection of non-linear crystals and birefringent crystals used for delay pre-compensation are derived based on approximation of non-saturated sum-frequency mixing of Gaussian pulses. We experimentally demonstrate the scheme and study its performance for a different combinations of BBO nonlinear crystals for the case of generation of sub-200 nm deep ultraviolet pulses by FHG of pulses delivered by a Ti:Sapphire ultrafast laser. Pulses with duration between 130 fs and 370 fs and pulse energy of 19 to 85 μJ were generated. It is shown, that in addition to its compactness and intrinsic stability, the scheme allows a superior spectrum and pulse quality.

Tunable, few-cycle, CEP-stable mid-IR optical parametric amplifier for strong field applications

We present a robust, three-stage optical parametric amplifier driven by a Ti:Sapphire ultrafast laser system that implements passive carrier-envelope phase stabilization and directly generates five-cycle mid-IR pulses by dispersion compensation. The source is based on potassium titanyl arsenate crystals and exploits intra-pulse difference-frequency seed generation in the mid-IR. This source will be particularly suited for applications in strong-field physics, such as high order harmonic generation and photoelectron spectroscopy.

Surface morphology and straight crack generation of ultrafast laser irradiated β-Ga2O3

Single crystal (010) β-Ga2O3 was irradiated by a Ti:sapphire ultrafast laser (150 fs pulse width) with varying fluences and a number of pulses in air ambient. Femtosecond laser-induced damage threshold of β-Ga2O3 is reported. Single pulse exposure results in surface morphological changes above a threshold laser fluence of 1.11 J/cm2. Laser-induced straight cracks aligned to the [001] crystallographic direction are observed in the laser irradiated regions, which are believed to be caused by laser-induced thermal stress, due to the unique low thermal conductivity and anisotropy associated with β-Ga2O3. Multiple pulse irradiation below the single pulse damage threshold fluence exhibited the formation of high spatial frequency laser-induced periodic surface structures. Electron backscattering diffraction and Raman spectroscopy suggested that there was no apparent phase transition of the irradiated β-Ga2O3 material for either single pulse or multiple pulse irradiation. This work serves as a starting point to further understanding the material properties of β-Ga2O3 and to unlock the potential for ultrafast laser material processing of β-Ga2O3.

Dynamics of femto- and nanosecond laser ablation plumes investigated using optical emission spectroscopy

We investigated the spatial and temporal evolution of temperature and electron density associated with femto- and nanosecond laser-produced plasmas (LPP) from brass under similar laser fluence conditions. For producing plasmas, brass targets were ablated in vacuum employing pulses either from a Ti:Sapphire ultrafast laser (40 fs, 800 nm) or from a Nd:YAG laser (6 ns, 1064 nm). Optical emission spectroscopy is used to infer the density and temperature of the plasmas. The electron density (ne) was estimated using Stark broadened profiles of isolated lines while the excitation temperature (Texc) was estimated using the Boltzmann plot method. At similar fluence levels, continuum and ion emission are dominant in ns LPP at early times (<50 ns) followed by atomic emission, while the fs LPP provided an atomic plume throughout its visible emission lifetime. Though both ns and fs laser-plasmas showed similar temperatures (∼1 eV), the fs LPP is found to be significantly denser at shorter distances from the target surface as well as at early phases of its evolution compared to ns LPP. Moreover, the spatial extension of the plume emission in the visible region along the target normal is larger for fs LPP in comparison with ns LPP.

Angular emission of ions and mass deposition from femtosecond and nanosecond laser-produced plasmas

We investigated the angular distribution of ions and atoms emanating from femto- and nanosecond laser-produced metal plasmas under similar laser fluence conditions. For producing plasmas, aluminum targets are ablated in vacuum employing pulses from a Ti:Sapphire ultrafast laser (40 fs, 800 nm) and an Nd:YAG laser (6 ns, 1064 nm). The angular distribution of ion emission as well as the kinetic energy distribution is characterized by a Faraday cup, while a quartz microbalance is used for evaluating deposited mass. The ion and deposited mass features showed that fs laser ablated plasmas produced higher kinetic energy and more mass per pulse than ns plumes over all angles. The ion flux and kinetic energy studies show fs laser plasmas produce narrower angular distribution while ns laser plasmas provide narrower energy distribution.

Autocorrelator designs for nonlinear optical microscopy

Nonlinear optical microscopy is a relatively new and rapidly growing field of optical engineering, where Ti:sapphire ultrafast laser sources and technologies are finding a wide application. Diagnostic techniques addressed to this kind of application have been widely developed in the last few years. Research efforts have been focused on the evaluation and eventual correction of laser pulse duration widening due to group velocity dispersion of microscope optics, and devices have been specially designed to perform second-order autocorrelation measurements at the objective focal plane. In the present work, innovative, simple setups and procedures are reported that make the best use of all the facilities and characteristics of the microscope itself, so that only a few optical components are needed to temporal characterize the laser pulse at the specimen plane.

Ultracompact autocorrelator for multiphoton microscopy.

Pulse temporal characterization is a fundamental task when operating a Ti:Sapphire ultrafast laser system for multiphoton microscopy applications. In the present report, an ultracompact autocorrelator setup and a simple procedure is reported to perform pulse width measurements at the focal plane of the microscope objective without the need of any further instrumentation, aside from a few optical elements, since the confocal microscope, detection, data acquisition, processing, and displaying capabilities are used.

Photoelectron spectroscopic determination of the energy bandwidths of high-order harmonics (7th–55th) produced by an ultrafast laser in neon

The energy bandwidths of high-order harmonics of a Ti:sapphire ultrafast laser are extracted from electron kinetic-energy measurements of the photoionization of gas-phase atoms and molecules. High-order harmonics of the 70 fs, 800 nm laser are produced by focusing $\ensuremath{\approx}2.5 \mathrm{mJ}$ pulses into a jet of neon gas and are frequency-separated by a grazing-incidence grating. Photoelectrons resulting from the ionization of gaseous samples are energy-analyzed with a magnetic bottle time-of-flight spectrometer. Energy broadening of the photoelectron peaks at low kinetic energies are a direct result of the energy bandwidths of the harmonics. The energy bandwidths of the harmonics are found to increase from $0.11(\ifmmode\pm\else\textpm\fi{}0.03) \mathrm{eV}$ (7th harmonic) to $0.37(\ifmmode\pm\else\textpm\fi{}0.03) \mathrm{eV}$ (45th harmonic) in a gradual manner. The higher-order harmonics (47th--55th) appear to reach a plateau at a value of $\ensuremath{\approx}0.43 \mathrm{eV}.$ Though a full theoretical treatment of bandwidths of the harmonics for the 70 fs driving pulse regime does not exist, the theories developed for shorter pulses $(<~30 \mathrm{fs})$ can give insight into the observed results.