John Hoose

Integral method for echelles covered with lossless or absorbing thin dielectric layers

We make a generalization of the integral method in the electromagnetic theory of gratings to study diffraction by echelles covered with dielectric lossless or absorbing layers. Numerical examples are given that show that, as in the resonance domain, the diffraction efficiency is more complicated than being a simple product of lossless diffraction efficiency curves and plane surface reflectivity.

Strong three-dimensional field localization and enhancement on deep sinusoidal gratings with two-dimensional periodicity

The study of total light absorption due to excitation of localized surface plasmons on deep metallic crossed gratings having a sinusoidal profile with a two-dimensional periodicity shows a very strong increase in the electric field intensity, reaching 800 times the incident intensity. The region with high intensity is strongly localized at the groove top and is characterized by a volume much smaller than the diffraction limit, both in transverse direction along the grating plane, and in longitudinal direction when going away from the grating surface. The field enhancement and its localization are much more pronounced than in shallow gratings.

White Light ac Interferometry For Multiple Laser Path Length Equalization

In the Omega laser fusion system, multiple laser beams are split from a single master oscillator. These beams are focused onto a reflective sphere which retroreflects the light back toward the beamsplitter. Any two of these beams can be operated as arms of an interferometer. With ac interferometry, the path lengths can be equalized to within one picosecond.

Two-dimensional gratings for low polarization dependent wavelength demultiplexing

Two-dimensional (crossed) diffraction gratings with sinusoidal or truncated pyramidal (trapezoidal) profiles are proposed to have diffraction efficiency almost independent of the incident polarization inside the optical communication spectral window 1.5-1.6 microm. The gratings are characterized by different periods in the two orthogonal directions, chosen to support only one dispersive diffraction order in addition to the zeroth (specular) one.

Low-polarization-dependence high-efficiency WDM

A diffraction-grating based demultiplexer is made to have low polarization dependence and high diffraction efficiency properties. The device is made is made of a Si grism working in reflection and having optimised grove profile easily manufactured by standard crystallographic etch of Si surface.

Concave holographic grating: optimization of the diffraction efficiency

The experimental comparison between two concave holographic gratings with identical recording geometries and different exposure conditions demonstrates some possibilities for the optimization of the integral diffraction efficiency.

Alignment System Devices For Medium Repetition Rate Glass Fusion Lasers

The OMEGA laser irradiation facility consists of a 24 arm Neodymium glass laser coupled to a spherical target irradiation chamber. A computer network is connected to the laser and target systems through a control room where operators can access any of the devices or subsystems within the facility. The facility is designed to produce 12 terawatt laser pulses and irradiate various materials to study laser-matter interactions at extremely high peak power. The system is capable of sustaining one target shot every 30 minutes.