Scott Buchter

Supercontinuum generation by nanosecond dual-wavelength pumping in microstructured optical fibers

We study experimentally the spectral evolution of supercontinua in two different microstructured fibers that are pumped with nanosecond pulses from dual-wavelength sources of either 1064/532 nm or 946/473 nm output. The experimental findings are compared with simulations based on numerically solving the nonlinear Schrödinger equation. The role of cascaded cross-phase modulation processes and the group-delay properties of the fiber are emphasized and demonstrated to determine the extent of the broadening of the continua to the visible wavelengths.

Thermal tuning of laser pulse parameters in passively Q -switched Nd:YAG lasers

Modifying the output pulses of a passively Q-switched Nd:YAG laser, operating at 1064 nm, was realized by heating the laser crystal. With the demonstrated laser setups, a 100 K temperature rise led to a more than 50% increase in the pulse energy and a more than 10% decrease in the pulse length. This method offers an effective way to tune the output of the laser without mechanical adjustment or a change of components.

Long distance active hyperspectral sensing using high-power near-infrared supercontinuum light source.

A hyperspectral remote sensing instrument employing a novel near-infrared supercontinuum light source has been developed for active illumination and identification of targets. The supercontinuum is generated in a standard normal dispersion multi-mode fiber and has 16 W total optical output power covering 1000 nm to 2300 nm spectral range. A commercial 256-channel infrared spectrometer was used for broadband infrared detection. The feasibility of the presented hyperspectral measurement approach was investigated both indoors and in the field. Reflection spectra from several diffusive targets were successfully measured and a measurement range of 1.5 km was demonstrated.

Creation of a narrow Bessel-like laser beam using a nematic liquid crystal

We present a simple and efficient method to convert a Gaussian laser beam into a Bessel-like beam with a long and narrow focal line by using a nematic liquid crystal with a high third-order nonlinearity.

Modeling the Time-Dynamics of Miniature Passively

The pulse-buildup in miniature passively Q-switched lasers occurs in a similar time-scale as the phonon-assisted thermalization of the laser manifolds. We study how the time-dynamics of the laser is affected by the thermalization and relaxation processes using a dimensionless geometrical rate equation model for a homogeneously broadened four-level gain medium. The pulse length is found to depend strongly on the thermalization rate when the ratio of the ground-state absorption cross section of the saturable absorber to the spectroscopic emission cross section of the laser transition is small (lsim 10). Numerically calculated design curves are shown for the 1064 nm transition in Nd:YAG, and guidelines are given for applying the model to other transitions. Experimental results are used for estimating the thermalization time constant of Nd:YAG for the 1 mum transition group and the ground-state absorption cross section of the Cr4+:YAG saturable absorber crystal.

Q

The aim of this work was to develop a cost effective hyperspectral instrument and to demonstrate the acquisition of IR reflection spectra over long distances.

-switched Lasers

We present the concept and both the experimental and computational study of a simple supercontinuum light source emitting at temporally highly stable output powers. The principle of the light source is based on a standard pulsed supercontinuum source combined with fiber-based dispersive time-stretching. This approach allows for tailored spectral emission in the visible at a power stability of below 1%. Furthermore, the computation indicates that highly stable light emission with this concept does not necessarily require highest possible input pulse repetition rates and longest dispersive fiber lengths.

Long range active hyperspectral target identification using near-IR supercontinuum light source

A simple and efficient method to convert a Gaussian laser beam into a nearly non-diverging Bessel-like beam or into a thin-walled hollow beam is described. The optical system used for the beam conversion consists of a thin liquid-crystal cell and one or two lenses. At certain parameter values, self-focusing of a Gaussian beam directly results in the formation of a narrow Bessel-like beam, and, if an additional lens is used to collimate the self-focused beam, the collimated beam shows an accurate ring-shaped profile.

Simple visible supercontinuum light source with true continuous-wave output power

Light sources with a broad spectral output and diffraction limited beam quality have a wide variety of present and future applications. A few of particular interest are hyperspectral laser radar for environmental monitoring, active hyperspectral imaging for detection and identification of objects, and speckle-free illumination. With the exception of systems based on amplified femto- or picosecond lasers, which are large and extremely complicated, pulse energies from supercontinuum laser sources have been limited to <10 microJoules which is generally not sufficient for the applications listed above. We present a simple technique to generate broadband light spanning several hundred nanometers in the near infrared with pulse energies of ~1 mJ, an improvement of approximately two orders of magnitude. The system is comprised of a Q-switched Nd:YAG laser and a very large mode area photonic crystal fiber. A combination of cascaded stimulated Raman scattering, four wave mixing, and self-phase modulation is responsible for the spectral broadening. Possibilities of scaling the output to the ~10 mJ level as well as extending the spectral coverage to the visible and mid-infrared will also be discussed.

Laser beam shaping using self-focusing in a nematic liquid crystal

The laser reported in this work has a gain medium pumped directly with an evanescent optical wave. Bright disk laser radiation is observed to propagate isotropically in a plane perpendicular to the capillary axis.