Dynamic kinetic resolution of racemic beta-haloalcohols: direct access to enantioenriched epoxides

The direct chemo-enzymatic DKR of racemic beta-haloalcohols is reported, yielding the corresponding optically active epoxides in a single step. The mutant haloalcohol dehalogenase HheC Cys153Ser Trp249Phe is used for the asymmetric ring closure, whereas racemization of the remaining enantiomer of the haloalcohol is achieved using the new iridacycle 3, one of the most effective racemization catalysts to date for beta-haloalcohols.     

Optically-pumped semiconductor squeezed-light generation

The theory presented shows that light emitted by low-temperature semiconductors under intense optical pumping (with fluctuations at the shot-noise level, SNL) should be amplitude-squeezed down to half the SNL at nonzeri frequencies. Amplitude squeezing may also be obtained at zero frequency when spontaneous carrier recombination is significant. It is essential that the optical gain depends on photon emission rate, e.g. as a result of spectral-hole burning. A commuting-number theory that agrees exactly with quantum theory for large particle numbers is employed. Comparison is made with results previously reported for three-level atom lasers.     

Photoresponse at the semiconductor-electrolyte junction: Influence of the space charge region width

By varying the potential applied to a semiconductor-electrolyte junction its spectral response is modified. The definition of a reduced parameter from the ratio between two spectral responses at two different potentials is achieved. A quantitative analysis of the behaviour of the illuminated junction is then possible, as well as a comparison with the theoretical Gärtner model without the knowledge of the incident photon flux. The experimental support is provided by the n-GaP-1M HClO₄ junction where the semiconductor presents an indirect and a direct energy transition. Thus a spectral region is determined where the Gärtner model and the experimental spectrum coincide and a value of the minority carrier diffusion length (L=0.31μm) is deduced.     

Broadly tunable single-frequency cw mid-infrared source with milliwatt-level output based on difference-frequency generation in orientation-patterned GaAs

A narrow-linewidth mid-IR source based on difference-frequency generation of an amplified 1.5 microm diode laser and a cw Tm-doped fiber laser in orientation-patterned (OP) GaAs has been developed and evaluated for spectroscopic applications. The source can be tuned to any frequency in the 7.6-8.2 microm range with an output power of 0.5 mW. The measured characteristics of the OP-GaAs sample demonstrate a high quality of the material.     

Two channel multilayer mirrors for astrophysics

A two-channel mirror reflecting both Fe-IX/X (λ = 17.1 nm) and He-II (30.4 nm) resonance lines at near normal incidence has been designed, fabricated and characterized. These two passbands are often chosen in space instruments designed for the observation of the solar corona. The mirror structure used for optimization is a superposition of two periodic multilayers with three components per period. It has been designed by using optimization software with an appropriate merit function. The theoretical reflectivity for both resonance lines can reach 0.25. It is shown that, by using a set of filters, one can select either the Fe-IX/X or the He-II channel. The spectral response of the two-channel mirror has been measured on synchrotron radiation source on a large wavelength range, from 12 nm to 35 nm. Experimental reflectivity reaches 0.32 for the Fe-IX/X line and 0.19 for the He-II line.     

Classical theory of laser noise

The classical theory of laser noise treats light in a classical manner, yet agrees with quantum theory for large particle numbers. The basic concept is that laser noise is caused by atomic jumps between lower and upper levels, and that atoms subjected to classically-prescribed optical fields are independent. The treatment of amplitude noise of single-mode cavities containing resonant three-level atoms is applicable to semiconductor lasers at moderate power. At high power one must account for the dependence of the gain on optical power and for state-occupancy fluctuations. The phasor theory that attributes noise to the beat between the oscillating field and the field spontaneously emitted in the mode by excited-state atoms cannot be understood consistently in semiclassical terms.