Intracavity frequency doubling of a diode-pumped external-cavity surface-emitting semiconductor laser.

We present a compact, robust, solid-state blue-light (490-nm) source capable of greater than 5 mW of output in a TEM(00) mode. This device is an optically pumped, vertical external-cavity surface-emitting laser with an intracavity frequency-doubling crystal.

Simple method of detecting ferroelectric domains with non-phase-matched second-harmonic generation.

We demonstrate a new method of detecting the presence of ferroelectric domains based on non-phase-matched second-harmonic generation. If a domain boundary is tilted relative to the input and output faces of the crystal, the far-field second-harmonic light consists of multiple beams, in contrast to the single beam generated in a single-domain crystal. The angular separation of the beams provides a measure of the tilt of the domain wall if the refractive-index difference n(2omega)-n(omega) is known.

Absolute measurement of the effective nonlinearities of KTP and BBO crystals by optical parametric amplification.

Absolute magnitudes of the effective nonlinearity, deff, were measured for seven KTP and six BBO crystals. The d(eff), were derived from the parametric gain of an 800-nm signal wave in the sample crystals when they were pumped by the frequency-doubled, spatially filtered light from an injectionseeded, Q-switched Nd:YAG laser. The KTP crystals, all type II phase matched with propagation in the X-Z plane, had d(eff) values ranging from 1.97 to 3.50 pm/V. Measurements of gain as a function of phase velocity mismatch indicate that two of the KTP crystals clearly contain multiple ferroelectric domains. For five type I phase-matched BBO crystals, d(eff) ranged from 1.76 to 1.83 pm/V, and a single type II phase-matched BBO crystal had a d(eff) of 1.56 pm/V. The uncertainty in our measurements of d(eff) values is ±5% for KTP and ±10% for BBO.

Automated construction and graphical presentation of protein blocks from unaligned sequences.

Protein blocks consist of multiply aligned sequence segments that correspond to the most highly conserved regions of protein families. Typically, a set of related proteins has more than one region in common and their relationship can be represented as a series of ungapped blocks separated by unaligned regions. Blockmaker is an automated system available by electronic mail (blockmaker@howard.fhcrc.org) and the World Wide Web (http://www.blocks.fhcrc.org4) that finds blocks in a group of related protein sequences submitted by the user. It adapts and extends existing algorithms to make them useful to biologists looking for conserved regions in a group of related proteins sequences. Two sets of blocks are returned, one in which candidate blocks are detected using the MOTIF algorithm and the other using a Gibbs sampler algorithm that has been adapted for full automation. This use of two block-finding methods based on completely different principles provides a 'reality check,' whereby a block detected by both methods is considered to be correct. Resulting blocks can be displayed using the information-based 'sequence logo' method, adapted to incorporate sequence weights, which provides an intuitive visual description of both the residue and the conservation information at each position. Blocks generated by this system are useful in diverse applications, such as searching databases and designing degenerate PCR primers. As an example, blocks made from amino acid sequences related to Caenorhabditis elegans Tc1 transposase were used to search GenBank, revealing that several fish and amphibian genomic sequences harbor previously unreported Tc1 homologs.

Frequency shifts in injection-seeded optical parametric oscillators with phase mismatch.

We have observed a frequency shift in the output signal pulses relative to the seed frequency in an injection-seeded, singly resonant, critically phase-matched, pulsed optical parametric oscillator in which phase mismatchwas intentionally introduced. The observed shifts can be large compared with the linewidth of the signal pulse, are approximately linear in phase mismatch, and increase with increasing pump fluence. We observe frequencyshifts of as much as +/-400 MHz for our 532-nm-pumped, potassium titanyl phosphate ring optical parametric oscillator. For zero phase mismatch, we observe nearly transform-limited linewidths of less than 130 MHz. Wecompare the experimental data to a simple analytic model that overestimates the shifts because it ignores pumpdepletion. We also compare our measurements with a numerical model that calculates the two-dimensional, transient electric fields and the resultant spectral distributions while explicitly including walk-off, diffraction, and pump depletion. We find good agreement between the experimental data and the results of this model.

Efficient two-photon-resonant frequency conversion in mercury: the effects of amplified spontaneous emission.

Numerical modeling of two-photon-resonant sum-frequency mixing in mercury vapor predicts efficiencies >10% for generation of 130.2-nm oxygen resonance light. The modeling indicates that power broadening of the two-photon resonance due to amplified spontaneous emission from the pumped level strongly influences the mixing process. Measurements of the broadening and the efficiencies for difference-frequency mixing are presented as a check of the model calculations.