Optical behavior analogous to electromagnetically induced transparency and absorption is observed in experiments using coupled fused-silica microspheres. This behavior results from interference between coresonant whispering-gallery modes of the two spheres. Coupled-resonator-induced transparency and absorption are observed. Which effect is seen depends on the strength of coupling of incident light from a tapered fiber into the first sphere and on the strength of coupling between the two spheres. The observed effects can enhance microresonator performance in various applications.

Saturated absorption spectroscopy is performed on the acetylene nu(1) + nu(3) band near 1532 nm inside photonic bandgap fibers of small (approximately 10 microm) and large (approximately 20 microm) core diameters. The observed linewidths are narrower in the 20 microm fiber and vary from 20 to 40 MHz depending on pressure and power. Variations in the background light transmission, attributed by others to surface modes, are significantly reduced in the 20 microm fiber. The optimum signal for use as a frequency reference in a 0.8 m long, 20 microm diameter fiber is found to occur at about 0.5 torr for 30 mW of pump power. The saturation power is found by modeling the propagation and attenuation of light inside the fiber.

Extended ultraviolet (EUV) emission characteristics of a laser-produced lithium plasma are determined with regard to the requirements of x-ray photoelectron spectroscopy. The main features of interest are spectral distribution, photon flux, bandwidth, source size, and emission duration. Laser-produced lithium plasmas are characterized as emitters of intense narrow-band EUV radiation. It can be estimated that the lithium Lyman-alpha line emission in combination with an ellipsoidal silicon/molybdenum multilayer mirror is a suitable EUV source for an x-ray photoelectron spectroscopy microscope with a 50-meV energy resolution and a 10-mum lateral resolution.

The development of new types of sophisticated soft x-ray sources requires the knowledge of their emission characteristics such as photon flux, spectral distribution, and size of the radiation source. Calibrated spectrographs for the soft x-ray region are needed to determine these properties. The components of a soft x-ray spectrograph consisting of a pinhole gold transmission grating and a charge coupled device (CCD) camera are calibrated at the radiometry laboratory of the Physikalisch-Technische Bundesanstalt using the synchrotron radiation facility BESSY. Two different kinds of CCD-based photon detectors (one thinned and back illuminated, one coated with a phosphorous layer) are compared with regard to their sensitivities in the spectral range between 50 eV and 1.7 keV. The results obtained for the thinned CCD are compared with theoretical calculations of the sensitivity

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We report the first experimental realization of all-optical electromagnetically induced transparency (EIT) via a pair of coherently interacting SiO2 microcavities in a one-dimensional SiO2/Si3N4 photonic crystal consisting of a distributed Bragg reflector (DBR). The electromagnetic interactions between the coupled microcavities (CMCs), which possess distinct Q-factors, are controlled by varying the number of embedded SiO2/Si3N4 bilayers in the coupling DBR. In case of weak microcavity interactions, the reflectivity spectrum reveals an all-optical EIT resonance which splits into an Autler-Townes-like resonance under condition of strong microcavity coupling. Our results open up the way for implementing optical analogs of quantum coherence in much simpler one-dimensional structures. We also discuss potential applications of CMCs.

Free-standing frequency-selective surfaces consisting of approximately 10-microm-thick copper films with cross-aperture arrays are found to be tunable toward lower frequencies by means of wet chemical etching. Center frequencies were tuned from 1.57 to 1.53 THz while maintaining high transmittance. Wet etching also adjusts bandwidth, peak transmittance, and sidelobe transmittance. The advantage of the wet-etch technique is demonstrated by employment of these devices as bandpass filters for difluoromethane-based terahertz lasers. Adjustment in aperture dimensions because of etching results in suppression of a competing laser line (133.93 microm) by 15 dB while maintaining high transmittance at the operating wavelength of 192.06 microm.

A radial multichannel pseudospark switch is integrated into a plasma focus system designed to generate soft x rays to determine switch durability in a long-term test. The operating parameters correspond to a repetition rate of up to 2 Hz, stand-off voltages of 10 kV and peak currents of 200 kA. Only minimal electrode erosion is witnessed after a serial test of 180 000 shots where the electrode surfaces are inspected after every 25 000 shots. The good condition of electrode surfaces suggests the possibility of an additional 200 000 shots, implying that for the given parameter range the lifetime of the multichannel pseudospark is at least four times longer than that of traditional high-current switches such as spark gaps. In a comparative test the performance of the multichannel pseudospark switch is evaluated against a multichannel spark gap. The results of these investigations show that the low-erosive pseudospark is well suited to substitute for spark gaps in high-current applications.