Intrapulse Frequency Research Articles

Electro-optic refractive index compensation applied to the intrapulse frequency stabilisation of a carbon dioxide TEA laser

A hybrid TEA CO2 laser with intracavity CdTe electro-optic modulator has been constructed. Heterodyne experiments demonstrate that the laser induced chirp of 0.88 MHz mu s-2 could be eliminated by application of the appropriate voltage waveform to the electro-optic modulator.

Electro-optic frequency shifts in a Q-switched CO2 laser

Measurements are described of intrapulse frequency shifts in an electro-optically Q-switched CO2 laser. These can be identified with the electro-optically induced refractive index changes in the modulator crystal. These refractive index changes, which play a fundamental role in the Q-switching process, can be exploited to provide either positive or negative frequency excursions. The frequency shift can be controlled between two extremes by the appropriate orientation of polarising elements. The effect may be eliminated to a high degree using an arrangement which provides maximum Q-switched power, or alternatively a large frequency shift (typically a quarter of the laser axial mode separation) may be produced with minimal Q modulation. This second mode of operation offers a valuable method of chirp correction in hybrid CO2 lasers.

Scaling laws for the intrapulse frequency stability of an injection mode selected TEA CO<inf>2</inf>laser

Heterodyne measurements of the intrapulse frequency behavior of an injection mode selected TEA CO 2 laser are presented. The frequency rose as the square of time at a rate varying linearly with energy and strongly dependent on spot size. These results are in accordance with a laser induced medium perturbative (LIMP) model, which allows the chirp in any TEA laser system to be predicted.

An investigation into the origin of frequency sweeping in a hybrid TEA CO2 laser

An analysis of the sources of the intrapulse frequency modulation in the hybrid TEA CO2 laser is presented. Two principal effects predominate: the falling frequency at the start of the pulse is shown to be due to plasma effects, while the increasing frequency during the remainder of the pulse arises from a laser induced refractive index perturbation. The significance of these results to the design of high stability pulsed lasers is discussed.

Courtship songs and genetic control of their acoustic characteristics in sibling species of the Drosophila melanogaster subgroup

Six sibling species of the melanogaster subgroup differ in their wing displays and in the acoustic characteristics of their courtship songs. D. melanogaster, D. simulans and D. mauritiana have distinct but similar courtship songs. D. mauritiana, which is allopatric to the others, produces, an ambivalent song with sine song frequency and intrapulse frequency like simulans and modal interpulse interval like melanogaster. These three species appear to be behaviourally more closely similar to each other than to the three African species D. yakuba, D. teissieri and D. erecta. The acoustic characteristics of the songs of interspecific hybrids, indicate that the interpulse interval and intrapulse frequency are quantitatively controlled by genes located on the autosomes. The ability to generate sine song may be controlled by one or more genes located on the X-chromosome, but an alternative possibility, of autosomal dominant inheritance, cannot be excluded.

The behavioural basis of overdominance in competitive mating success at the ebony locus of Drosophila melanogaster

Male files homozygous for the gene ebony 11 are partially blind, and at a disadvantage in competitive mating. The courtship of the mutant males is deficient in wing vibration stimulation, which is characterized by a low proportion of sine song and a high intra-pulse frequency. Males heterozygous for ebony have normal vision, but show an increase in courtship song, and are superior in competitive mating to wild type males. The auditory characteristics of courtship song produced by heterozygous males are indistinguishable from those of wild type, and their superiority in competitive mating success is due to overdominance involving this specific element of male courtship behaviour.

Control of TRAPATT oscillations by optically generated carriers

It is demonstrated that, by generating carriers optically within a TRAPATT oscillator, startup jitter can be held to a short duration over a wider range in operating conditions, and intrapulse frequency drift may be virtually eliminated. In addition, optical carrier generation is shown to provide the basis of a novel frequency tuning technique capable of producing extremely fast intrapulse frequency switching.