Generation of amplitude-squeezed light from a room-temperature Fabry-Perot semiconductor laser

Amplitude-squeezed light with intensity fluctuations 29% below the standard quantum limit (SQL) is produced from a pump-suppressed room-temperature semiconductor laser, corresponding to 41% below the SQL after correction for detection efficiency. Excess noise, which degrades the observed squeezing, appears to be associated with the presence of weak longitudinal side modes

Linewidth reduction and frequency stabilization of a semiconductor laser with a combination of FM sideband locking and optical feedback

We describe a novel method for semiconductor laser noise reduction that uses a combination of optical and electronic feedback. A Doppler-free Faraday resonance in Cs vapor provided both optical feedback and discrimination for an electronic feedback scheme incorporating FM sideband spectroscopy. The introduction of electronic feedback further reduced the low-frequency fluctuation noise power by more than 2 orders of magnitude, resulting in a linewidth of 1.4 kHz

Self-quenching of the semiconductor laser linewidth below the Schawlow-Townes limit by using optical feedback

We demonstrate theoretically and experimentally self-quenching of the fundamental semiconductor laser frequency fluctuations to a level that is orders of magnitude below the Schawlow-Townes limit for a solitary laser. It is shown that the main operative mechanism is the combined action of a frequency-dependent internal loss and amplitude-to-phase coupling. The internal frequency-dependent loss is introduced by means of spectrally narrow external optical feedback, which provides a strong frequency-dependent dispersion. Linewidth reduction by a factor of 2 X 10^3 is demonstrated by using a narrow Doppler-free Faraday resonance in Cs vapor

Amplitude noise reduction in semiconductor lasers with weak, dispersive optical feedback

We present the theory and measurements of the amplitude noise spectrum from a semiconductor laser with weak optical feedback (Pfb/Pout ~10^-6) from an external cavity containing an element of dispersive loss. The laser noise is found to be reduced over most of the low-frequency spectrum, although an increase in the noise is observed at frequencies corresponding to multiples of the external-cavity free spectral range. The low-frequency noise reduction closely follows theoretical predictions, and a reduction of as much as 7 dB is measured at an injection current of 1.5 times the threshold current. The potential of this method for contributing to the production of amplitude-squeezed light is discussed

On the Lystrosaurus zone and its fauna with special reference to some immature Lystrosauridae

Main articleIn the past, collecting from the middle Beaufort Beds or Lystrosaurus zone has been badly neglected by field workers mainly due to the monotonous occurrence of the genus Lystrosaurus. Collecting has mostly been undertaken in such areas as the Harrismith Commonage, Oliviershoek Pass, Bergville or where there was a good possibility of finding either Thrinaxodon, Glochinodontoides or other faunal remains more exciting than Lystrosaurus.Non

Notes on some fossil pockets and bone beds in the Cynognathus- zone in the Burghersdorp and Lady Frere districts

Main articleMost palaeontological field workers are familiar with the blue to green shales and maroon to red mudstones, as well as the fine-grained greenish-blue sandstones, of the Cynognathus-zone, all these colours contributing to its general patchy appearance. Heights within the zone can unfortunately not be determined reliably with the assistance of particular colour sequences, but a conspicuous and persistent sandstone horizon marks the middle level of the zone. Our knowledge of the manner in which fossils occur both above and below this horizon is not satisfactory.Non

The stratigraphic distribution and occurrence of South African fossil Amphibia in the Beaufort beds

Main articleA short account is given of the distribution and occurrence of fossil amphibians from the Beaufort succession, based on analyses of specimens in various South African and overseas institutions. Their occurrence is based on the re-examination of all the localities which have yielded amphibian remains to date and on field observations during the course of collecting. Attention is drawn to the paucity of fossil amphibians throughout the Beaufort palaeontological record. Possible causes of this paucity are discussed.Non

Preliminary report on a clutch of six dinosaurian eggs from the upper Triassic Elliot Formation, Northern Orange Free State

Main articleA clutch of six dinosaurian eggs, containing foetal skeletons of as yet uncertain taxonomic affinity, from the Elliot Formation (Red Bed Stage), northern Orange Free State, seems to be the first record of fossil eggs of Upper Triassic age. As preserved the eggs have a long axis of 65 mm, with a short axis of approximately 55 mm. The egg “shell” is exceptionally thin; fragments removed from one of the specimens have an estimated thickness of 0,5 mm. Additional preparation work is at present being undertaken on a reasonably well-preserved skull in one of the eggs and a more detailed description of the specimen and possible parentage will appear at a later date.Non

On some fossil Arthropoda from the Limeworks , Makapansgat, Potgietersrus

Main articleThe fossil arthropod remains from the Limeworks deposit consist of puparial and dung ball casts from the Lower Phase I (Member 3) through to the Upper Phase I (Member 4) breccias. The puparial stages are represented in two gross sizes; cuticular remains and segmentation are evident in a few. Possible palaeoenvironmental implications based on the puparial remains and their state of preservation are briefly discussed. A remarkably well preserved fossilised juvenile centipede from the Lower Phase I (Member 3) breccia is placed on record for the first time.Non

A fossil Orycteropus from the Limeworks quarry, Makapansgat, Potgietersrus

Main articleThe family Orycteropodidae (Grey 1821) comprises the antbears of the Old World and is known from fossil evidence to have existed in Europe, Asia and Madagascar, but the living species, confined to one single genus, now occur only on the continent of Africa..Non