Advances In Ultrafast Laser Technology Research Articles

High-field nonlinear optical response and phase control in a dielectric laser accelerator

Advances in ultrafast laser technology and nanofabrication have enabled a new class of particle accelerator based upon miniaturized laser-driven photonic structures. However, developing a useful accelerator based on this approach requires control of the particle dynamics at field intensities approaching the damage limit. We measure acceleration in a fused silica dielectric laser accelerator driven by fields of up to 9 GV m−1 and observe a record 1.8 GV m−1 in the accelerating mode. At these intensities the dielectric is driven beyond its linear response and self-phase modulation changes the phase velocity of the accelerating mode, reducing the average gradient to 850 MeV m−1. We show that free-space optics can be used to compensate this dephasing and demonstrate that tailoring the laser phase and amplitude can facilitate optimization of the beam dynamics. This could enable MeV scale energy gain in a single stage and pave the way towards applications in scientific, industrial, and medical fields.

ChemInform Abstract: Recent Advances on Ultrafast X‐Ray Spectroscopy in the Chemical Sciences

AbstractReview: 141 refs.

Use of the Gerchberg–Saxton algorithm in optimal coherent anti-Stokes Raman spectroscopy

We are utilizing recent advances in ultrafast laser technology and recent discoveries in optimal shaping of laser pulses to significantly enhance the stand-off detection of explosives via control of molecular processes at the quantum level. Optimal dynamic detection of explosives is a method whereby the selectivity and sensitivity of any of a number of nonlinear spectroscopic methods are enhanced using optimal shaping of ultrafast laser pulses. We have recently investigated the Gerchberg-Saxton algorithm as a method to very quickly estimate the optimal spectral phase for a given analyte from its spontaneous Raman spectrum and the ultrafast laser pulse spectrum. Results for obtaining selective coherent anti-Stokes Raman spectra (CARS) for an analyte in a mixture, while suppressing the CARS signals from the other mixture components, are compared for the Gerchberg-Saxton method versus previously obtained results from closed-loop machine-learning optimization using evolutionary strategies.

Surrounded by complications

There is a long history of gas-phase studies of bimolecular reactions, but the presence of surrounding molecules complicates analogous studies in solution. Now, advances in ultrafast laser technology have enabled the detailed study of vibrational energy release in a reaction in solution.

Ultrafast Dynamics in Reverse Micelles

Recent advances in ultrafast laser technology have spurred investigations of microheterogeneous solutions. In particular, researchers have explored details of reverse micelles (RMs), which present isolated droplets of polar solvent sequestered from a continuous nonpolar phase by a surfactant layer. This review explores recent studies utilizing a variety of ultrafast laser techniques to uncover details about structure and dynamics in various RMs. Using ultrafast vibrational spectroscopy, researchers have probed hydrogen-bond dynamics and vibrational energy relaxation in RMs. These studies have developed our understanding of reverse micellar structure, identifying varying water environments in the RMs. In a plethora of experiments employing probe molecules, researchers have explored the confined environment presented by RMs and their impact on a range of chemical reactions. These studies have shown that confinement, rather than the specific interactions with surfactants, is an important factor determining the impact of the reverse micellar environment on the chemistry.

Temporal pulse manipulation and consequences for ultrafast laser processing of materials

Following advances in ultrafast laser technology as a reliable tool for material probing and processing, we discuss various options for control and optimization. The possibility to tailor the temporal shape of ultrashort laser pulses enables extended opportunities for material processing. The concept of optimizing laser interactions is based on the possibility to regulate the energy delivery so that control of laser-induced phenomena can be achieved and quality structures can be realized. An experimental demonstration of the possibility to design excitation sequences tailored with respect to the material response is described, laying the groundwork for adaptive optimization in materials structuring. We show that under particular irradiation conditions involving modulated excitation, the energy flow can be controlled and the material response can be guided to improve processing results. This is particularly important for processing brittle materials. Further examples are given to illuminate the possibility to optimize the kinetic properties of ions emitted from laser-irradiated semiconductors, using excitation sequences synchronized with the solid-to-liquid transformation time. Versatile sub-kilo-electron-volt ion beams are obtained, exploiting transitions to supercritical fluid states with minimal energetic expenses. Temporally selective irradiation can thus open up efficient thermodynamic paths, unfolding interesting perspectives for intelligent, feedback-assisted processing of materials.

Few-optical-cycle laser pulses: from high peak power to frequency tunability

Recent advances in ultrafast laser technology have led to the generation of light pulses comprising few optical cycles employing different compression techniques. In particular, two techniques have been developed, which allow addressing the issues of high peak power or frequency tunability in a wide spectral range, namely: the hollow-fiber compression technique and the optical parametric amplification. The paper analyzes the general scheme of pulse compression and reports on the most interesting results obtained using the above-mentioned techniques. The combination of spectral broadening in a gas-filled hollow fiber with ultrabroad-band dispersion control, has led to the generation of pulses with duration of /spl sim/5 fs with peak powers up to 0.11 TW. Using optical parametric amplifiers with different configurations sub-15-fs laser pulses have been generated tunable in the visible and in the near-infrared.

Ultrabroadband femtosecond lasers

The exploitation of soliton-like pulse shaping mechanisms and the optimization of phase dispersion in broadband self-modelocked solid state laser oscillators have led to unprecedented advances in ultrafast laser technology. This paper reviews the basic physical mechanisms governing pulse formation and addresses the requirements for optimum performance of these novel ultrashort pulse laser sources. These considerations together with the demonstration of /spl ap/10 fs pulse generation from a Ti:sapphire laser suggest that a family of solid-state laser oscillators with comparable performance can be developed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Transient solvation of polar dye molecules in polar aprotic solvents

Subpicosecond fluorescence spectroscopy of the polar dye molecules coumarin 311 and coumarin 102 has been used to measure the microscopic solvation dynamics of several polar aprotic solvents. The measured solvation times are significantly longer than the longitudinal relaxation times τ1 of the solvents. τ1 is the predicted time for solvation according to dielectric continuum theory. The experiments were made with a newly constructed subpicosecond ultraviolet emission apparatus that takes advantage of recent advances in ultrafast laser technology. The newly developed, time saving procedure [Nagarajan et al., J. Chem. Phys. 86, 3183 (1987)] for measuring the microscopic solvation response functions was used in this research.