Linewidth reduction in a large-smile laser diode array

We present theory and simulations for a spectral narrowing scheme for laser diode arrays (LDAs) that employs optical feedback from a diffraction grating. We calculate the effect of the so-called smile of the LDA and show that it is possible to reduce the effect by using a cylindrical lens set at an angle to the beam. The scheme is implemented on a 19-element LDA with smile of 7.6 mu m and yields frequency narrowing from a free-running width of 2 to 0.15 nm. The experimental results are in good agreement with the theory. (c) 2005 Optical Society of America.

Laser frequency locking by direct measurement of detuning

We present a new method of laser frequency locking in which the feedback signal is directly proportional to the detuning from an atomic transition, even at detunings many times the natural linewidth of the transition. Our method is a form of sub-Doppler polarization spectroscopy, based on measuring two Stokes parameters (I-2 and I-3) of light transmitted through a vapor cell. It extends the linear capture range of the lock loop by as much as an order of magnitude and provides frequency discrimination equivalent to or better than those of other commonly used locking techniques. (C) 2004 Optical Society of America

Adaptive phase measurements for narrowband squeezed beams

We have previously [Phys. Rev. A 65, 043803 (2002)] analyzed adaptive measurements for estimating the continuously varying phase of a coherent beam, and a broadband squeezed beam. A real squeezed beam must have finite photon flux N and hence can be significantly squeezed only over a limited frequency range. In this paper we analyze adaptive phase measurements of this type for a realistic model of a squeezed beam. We show that, provided it is possible to suitably choose the parameters of the beam, a mean-square phase uncertainty scaling as (N/kappa)(-5/8) is possible, where kappa is the linewidth of the beam resulting from the fluctuating phase. This is an improvement over the (N/kappa)(-1/2) scaling found previously for coherent beams. In the experimentally realistic case where there is a limit on the maximum squeezing possible, the variance will be reduced below that for coherent beams, though the scaling is unchanged.

Lasers - An effective artificial source of radiation for the cultivation of anoxygenic photosynthetic bacteria

The laser diode (LD) is a unique light source that can efficiently produce all radiant energy within the narrow wavelength range used most effectively by a photosynthetic microorganism. We have investigated the use of a single type of LID for the cultivation of the well-studied anoxygenic photosynthetic bacterium, Rhodobacter capsulatus (Rb. capsulatus). An array of vertical-cavity surface-emitting lasers (VCSELs) was driven with a current of 25 mA, and delivered radiation at 860 nm with 0.4 nm linewidth. The emitted light was found to be a suitable source of radiant energy for the cultivation of Rb. capsulatus. The dependence of growth rate on incident irradiance was quantified. Despite the unusual nearly monochromatic light source used in these experiments, no significant changes in the pigment composition and in the distribution of bacteriochlorophyll between LHII and LHI-RC were detected in bacterial cells transferred from incandescent light to laser light. We were also able to show that to achieve a given growth rate in a light-limited culture, the VCSEL required only 30% of the electricity needed by an incandescent bulb, which is of great significance for the potential use of laser-devices in biotechnological applications and photobioreactor construction. (c) 2006 Wiley Periodicals, Inc.

Quantum memory scheme based on optical fibers and cavities

An optical quantum memory scheme using two narrow-linewidth cavities and some optical fibers is proposed. The cavities are connected via an optical fiber, and the gap of each cavity can be adjusted to allow photons with a certain bandwidth to transmit through or reflect back. Hence, each cavity acts as a shutter and the photons can be stored in the optical fiber between the cavities at will. We investigate the feasibility of using this device in storing a single photon. We estimate that with current technology storage of a photon qubit for up to 50 clock cycles (round trips) could be achieved with a probability of success of 85%. We discuss how this figure could be improved.

Further evidence of linkage at 7p22 with familial hyperaldosteronism type II

Primary aldosteronism (PAL) is caused by the autonomous over-production of aldosterone. Once thought rare, it is now reported to be responsible for 5–10% of hypertension. Familial hyperaldosteronism type II (FH-II), unlike familial hyperaldosteronism type I, is not glucocorticoid-remediable and not associated with the hybrid CYP11B1/CYP11B2 gene mutation. At least five times more common than FH-I, FH-II is clinically, biochemically and morphologically indistinguishable from apparently sporadic PAL, suggesting that its incidence maybe even higher. Studies performed in collaboration with C Stratakis (NIH, Bethesda) on our largest Australian FH-II family (eight affected members) demonstrated linkage at chromosome 7p22. Similar linkage at this region was also found in a South American FH-II family (DNA provided by MI New, Presbyterian Hospital, New York). Mutations in the exons and intron/exon boundaries of the PRKARIB gene (which resides at 7p22 and is closely related to PRKARIA gene mutated in Carney complex) have been excluded in our largest Australian FH-II family. Using more finely spaced markers, we have confirmed linkage at 7p22 in these 2 families, and identified a second Australian family with evidence of linkage at this locus. The combined multipoint LOD score for these 3 families is 4.87 (θ=0) with markers D7S462 and D7S2424, which exceeds the critical threshold for genome-wide significance suggested by Lander and Kruglyak (1995), providing strong support for this locus harbouring mutations responsible for FH-II. A newly identified recombination event in our largest Australian family has narrowed the region of linkage by 1.8 Mb, permitting exclusion of approximately half the genes residing in the original reported 5Mb linked locus. In addition, we have strongly excluded linkage to these key markers in two Australian families (maximum multipoint LOD scores −3.51 and −2.77), supporting the notion that FH-II may be genetically heterogeneous. In order to identify candidate genes at 7p22, more closely spaced markers will be used to refine the locus, as well as single nucleotide polymorphism analysis.

Further evidence of linkage at 7p22 with familial hyperaldosteronism type II and exclusion of genetic defects in the RBAK coding regions

Once thought rare, primary aldosteronism (PAL) is now reported to be responsible for 5–10% of hypertension. Unlike familial hyperaldosteronism type I (FH-I), FH-II is not glucocorticoidremediable and not associated with the hybrid CYP11B1/CYP11B2 gene mutation. At least five times more common than FH-I, FH-II is clinically indistinguishable from apparently sporadic PAL, suggesting an even higher incidence. Studies performed in collaboration with C Stratakis (NIH, Bethesda) on our largest Australian family (eight affected members) demonstrated linkage at chromosome 7p22. Linkage at this region was also found in a South American family (DNA provided by MI New, Mount Sinai School of Medicine, New York) and in a second Australian family. The combined multipoint LOD score for these 3 families is 4.61 (q = 0) with markers D7S462 and D7S517, providing strong support for this locus harbouring mutations responsible for FH-II. A newly identified recombination event in our largest Australian family has narrowed the region of linkage by 1.8 Mb, permitting exclusion of approximately half the genes residing in the originally reported 5 Mb linked locus. Candidate genes that are involved in cell cycle control are of interest as adrenal hyperplasia and adrenal adenomas are common in FH-II patients. A novel candidate gene in this linked region produces the retinoblastoma-associated Kruppel-associated box protein (RBaK) which interacts with the retinoblastoma gene product to repress the expression of genes activated by members of the E2F family of transcription factors.

XSophe, a computer simulation software suite for the analysis of electron paramagnetic resonance spectra

The XSophe computer simulation software suite consisting of a daemon, the XSophe interface and the computational program Sophe is a state of the art package for the simulation of electron paramagnetic resonance spectra. The Sophe program performs the computer simulation and includes a number of new technologies including; the SOPHE partition and interpolation schemes, a field segmentation algorithm, homotopy, parallelisation and spectral optimisation. The SOPHE partition and interpolation scheme along with a field segmentation algorithm greatly increases the speed of simulations for most systems. Multidimensional homotopy provides an efficient method for accurately tracing energy levels and hence tracing transitions in the presence of energy level anticrossings and looping transitions and allowing computer simulations in frequency space. Recent enhancements to Sophe include the generalised treatment of distributions of orientational parameters, termed the mosaic misorientation linewidth model and a faster more efficient algorithm for the calculation of resonant field positions and transition probabilities. For complex systems the parallelisation enables the simulation of these systems on a parallel computer and the optimisation algorithms in the suite provide the experimentalist with the possibility of finding the spin Hamiltonian parameters in a systematic manner rather than a trial-and-error process. The XSophe software suite has been used to simulate multifrequency EPR spectra (200 MHz to 6 00 GHz) from isolated spin systems (S > ~½) and coupled centres (Si, Sj _> I/2). Griffin, M.; Muys, A.; Noble, C.; Wang, D.; Eldershaw, C.; Gates, K.E.; Burrage, K.; Hanson, G.R."XSophe, a Computer Simulation Software Suite for the Analysis of Electron Paramagnetic Resonance Spectra", 1999, Mol. Phys. Rep., 26, 60-84.