High order kinoforms as a broadband achromatic diffractive optics for terahertz beams.

We discuss thin optical structures that allow chromatic aberrations to be avoided in the THz domain. The paper contains the theoretical considerations, computer modeling and experimental evaluation of the high order kinoform diffractive elements in the THz range. According to the obtained results application of the high order kinoforms enables broadband operation in the THz range.

Highly precise determination of optical constants and sample thickness in terahertz time-domain spectroscopy.

Time-domain spectroscopy allows fast and broadband measurement of the optical constants of materials in the terahertz domain. We present a method that improves the determination of the optical constants through simultaneous determination of the sample thickness. This method could be applied to any material with moderate absorption and requires only two measurements of the temporal profile of the terahertz pulses: a reference one without the sample and one transmitted through the sample.

Grating-assisted phase-matched second-harmonic generation from a polymer waveguide.

Diffraction gratings can be used to achieve phase matching between the fundamental modes of a slab or confined waveguide. Compared with the usual techniques such as quasi-, Cerenkov, and intermodal phase matching, the matching method used here involves spatial harmonics of the guided electromagnetic field that are generated by the corrugated grating. This grating acts simultaneously as a linear waveguide coupler at both the pump and harmonic frequencies. Using the third spatial harmonic, we report what we believe to be the first observation of grating-assisted phase-matched second-harmonic generation between counterpropagating TM(0) modes of an organic waveguide.

Grating-enhanced second-harmonic generation in polymer waveguides: role of losses.

A numerical study of second-harmonic (SH) generation in a corrugated polymer waveguide is performed with a rigorous electromagnetic theory. Comparison with experiment reveals the role of losses inside the waveguide-small losses do not significantly affect the nonresonant response and reduce the resonant enhancement of SH generation. High losses can lead to the opposite effect-instead of enhancement, dips in the SH efficiency are observed in the vicinity of guided-wave excitation. The peculiarities of the angular dependencies of SH generation are explained from the phenomenological point of view, and the role of phase matching is discussed.

Optical waveguides fabricated by ion exchange in high-index commercial glasses.

We present the fabrication process and the optical characterization of waveguides made by an ion-exchange technique in high-index D0035 and D0042C Corning glasses. We fabricate monomode channel waveguides in both kinds of glasses by exchange through a metallic mask.

Experimental results of second-harmonic generation from a polyurethane waveguide on a silver grating coupler.

Second-harmonic generation by excitation of guided modes and the surface plasmon in a polyurethane-coated silver grating coupler is presented. In order to study the spectral dependence of the second-harmonic efficiency, two different pump wavelengths are used, 1064 and 1319 nm. For the longer-wavelength pump we observe a large enhancement of the second-harmonic efficiency as the incident angle is scanned through an electromagnetic resonance, whereas for the shorter-wavelength pump the second-harmonic wavelength falls within the absorption band of the polymer, and we observe unexpected minima instead of maxima.

Simple method of measuring the duration of short laser pulses.

We present a simple method to determine the duration of short laser pulses by measuring the efficiency of a second harmonic generation experiment.

High index gradient in glass by ion exchange.

A gradient index having 0.22 as maximum value has been obtained in a TiF(6) Schott glass by the ion exchange technique. Index profiles and ionic concentration are presented. The reasons for such a high gradient are analyzed.

Realization of Schmidt plates by ion exchange in glass.

A new technique is presented to realize Schmidt plates by ionic exchange controlled by electric field into adjacent areas. The shape and optical path in these areas may be adjusted very accurately. A preliminary plate has been made with three areas, and results are analyzed.