We report on the terahertz (THz) emission from GaSb surfaces with modified surface stochiometry. While very weak emission is observed from virgin GaSb wafers, the emission is significantly increased by a single thermal treatment of the wafers. Optimum emission is observed for 500°C thermal annealing. The reason for the THz emission is a surface electric field induced by thermal decomposition of the surface, as corroborated by Raman spectroscopy.
The present article discusses an optical concept for the characterization of diffractive micromirror arrays (MMAs) within an extended wavelength range from the deep ultra-violet up to near-infrared. The task derives from the development of a novel class of MMAs that will support programmable diffractive properties between 240 nm and 800 nm. The article illustrates aspects of the achromatic system design that comprises the reflective beam homogenization with divergence control and coherence management for an appropriate MMA illumination as well as the transfer of phase modulating MMA patterns into intensity profiles for contrast imaging. Contrast measurements and grey scale imaging demonstrate the operation of the characterization system and reflect the encouraging start of technology development for multispectral, diffractive MMAs
We report on our investigation to precisely actuate diffractive micromirror arrays (MMA) with an accuracy of /100. The test samples consist of analog, torsional MEMS arrays with 65 536 (256x256) mirror elements. These light modulators were developed for structured illumination purposes to be applied as programmable mask for life science and semiconductor microscopy application. Main part of the work relies on the well known characterization of MEMS mirrors with profilometry to automatically measure and approximate the MMA actuation state with high resolution. Examples illustrate the potential of this strategy to control the tilt state of many thousand micromirrors within the accuracy range of the characterization tool. In a dynamic range between 0 and >250 nm the MMA deflection has been precisely adjusted for final MMA application in the deep-UV - VIS - NIR spectral range. The optical properties of calibrated MMAs are tested in a laser measurement setup. After MMA calib ration an increased homogeneity and improved image contrast are demonstrated for various illumination patterns
We report on time resolved femtosecond carrier dynamics in molecular beam epitaxy grown GaNxAs1−x with a nitrogen fraction of 1.3%. The intraband carrier relaxation time in GaNxAs1−x is found to be significantly larger than in GaAs. We compare the experimental results with carrier-polar optical phonon scattering rates calculated within the band anticrossing model. From the results we conclude that the slowing down of the carrier relaxation is a result of the strongly modified band structure in GaNxAs1−x.
We describe charging effects on spatial light modulators (SLM). These light modulators consist of up to one million mirrors that can be addressed individually and are operated at a frame rate of up to 2 kHz. They are used for deep ultraviolet (DUV) mask writing where they have to meet very high requirements with respect to accuracy. To be usable in a mask-writing tool, the chips have to be able to work under DUV light and maintain their performance with high accuracy over a long period of time. Charging effects are a problem frequently encountered with MEMS, especially when they are operated in an analog mode. In this work, the issue of charging effects in SLMs used for microlithography, their causes and methods of their reduction or elimination, by means of addressing methods as well as technological changes, is discussed. The first method deals with the way charges can accumulate within the actuator. It is a simple method that requires no technological changes but cannot always be implemented. The second involves the removal of the materials within the actuator where charges can accumulate
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