Stationary Dark Research Articles

Optical vortex trapping of particles

We demonstrate three-dimensional trapping of low-index particles (20-microm-diameter hollow glass spheres in water) by using a single, strongly focused, stationary dark optical vortex laser beam. The holographically generated vortex, which is similar to a TEM(01)* mode beam, was also used to trap and form ring patterns of high-index particles.

Stability of stationary dark waves guided by nonlinear surfaces and waveguides

The stability properties of stationary waves supported by a linear self-defocusing surface and a linear thin film sandwiched between two identical self-defocusing bounding media are investigated analytically with exact solutions. It is found that dark surface and gray guided modes are stable, whereas higher-order dark guided modes are unstable. A finite-difference beam propagation method is used to confirm these analytical results, to study the propagation of some nonstationary solutions, and to show that end-firing excitation of stable modes should be possible.

Stationary and radiating dark solitons of the third order nonlinear Schrödinger equation

Solitons of the “defocusing” nonlinear Schrödinger equation with an additional third derivative term are considered. The solitons are of the dark type and can be both stationary and radiating. Necessary conditions for the existence of stationary dark solitons with constant asymptotics are derived. An analytical description of the soliton radiation is given and the respective soliton attenuation is calculated. The existence of stationary dark solitons with rippled asymptotics is also suggested.

Existence of solitary waves in optical fibers owing to the mutual support between bright and dark pulses

We introduce a new type of solitary wave in a lossless single-mode fiber in which a bright solitonlike pulse in the anomalous-dispersion range propagates together with a stationary dark pulse in the normal-dispersion range. Such a solitary wave can be generated by launching a bright pulse in the anomalous-dispersion range together with a long pulse of the same speed in the normal-dispersion range into a fiber. The results of numerical simulations show that the dark pulse is not a dark soliton. The generation and maintenance of such a solitary wave are attributed to the mutual chirping through cross-phase modulation between those two waves in the anomalous- and normal-dispersion ranges.

Non-equilibrium Fermi energy profiles of electrons and holes over the semiconductor space charge layer at stationary dark or photocurrents

The properties of semiconductor electrodes at larger band bending and under stationary dark or photocurrents, may be discussed in terms of non-equilibrium Fermi energy profiles of electrons and holes over the space charge layer, which were calculated from balance and classical Nernst-Planek transport equations. In this paper particularly the anodic regime of n-type semiconductors has been investigated. The features of non-equilibrium Fermi energy profiles of majority and minority carriers are elucidated. The problem of termination of the Mott-Schottky range at large band bending is again considered and the effects of competition of classical transport and tunnelling are qualitatively discussed.

Kinetics of anodic dark and photodissolution of n-GaAs and n-GaP electrodes

This paper provides a theoretical survey and further experimental data of kinetically controlled stationary dark and photocurrents on n-GaAs and n-GaP electrodes. The mechanism of anodic photodissolution is treated in greater detail, taking explicitly into account a sequence of kinetic steps. The possibility to detect partial charge transfer steps in stationary photocurrent-voltage curves is examined and related experimental data are discussed. Effects of photoinduced surface layer formation which takes place under certain conditions are briefly reported.

Sustained and transient responses by cat striate cells to stationary flashing light and dark bars

Sustained and transient responses by cat striate cells to stationary flashing light and dark bars

Dark adaptation and receptive field organisation of cells in the cat lateral geniculate nucleus

The receptive fields of LGN cells were investigated with stationary light and dark spot and annulus stimuli. Stimulus size and background intensity were varied while stimulus/background contrast was kept constant. The speed of dark adaptation vaired considerably from cell to cell. Dark adaptation made responses more sustained in all neurones and eliminated the oscillatory on-responses evoked under some conditions in the light-adapted cells. Dark adaptation led also to a disappearance of early phasic inhibition in on-responses, and increased response rise time and latency. The power of surround responses to inhibit centre responses decreased slightly at low levels of light adaptation in LGN cells but much less than in retinal ganglion cells. Some other traces of changing retinal surround effects also appeared inthe LGN on dark adaptation. For example, the functional size of receptive fields increased at low levels of illuminance as has been observed in retinal ganglion cells and the receptive fields as estimated from response peaks were larger than those estimated from sustained components.

1102. Photoluminescent properties and amplification coefficient of CdS and CdSe single crystals at electron-beam excitation

This paper provides a theoretical survey and further experimental data of kinetically controlled stationary dark and photocurrents on n-GaAs and n-GaP electrodes.The mechanism of anodic photodissolution is treated in greater detail, taking explicitly into account a sequence of kinetic steps. The possibility to detect partial charge transfer steps in stationary photocurrent-voltage curves is examined and related experimental data are discussed.Effects of photoinduced surface layer formation which takes place under certain conditions are briefly reported.

A Movable Fluoroscope for Fluoroscopy and Serial Radiography without the use of a Dark Room

In a recent survey of the literature on fluoroscopy made at the Boston Medical Library, Yale Medical Library, and the New York Academy of Medicine, I was amazed to find that little or no attempt has ever been made to do fluoroscopy by any other method than the dark room. Dr. George C. Johnson (1), of Pittsburgh, in 1905 wrote an article descriptive of a device whereby he allowed a pyramid of rays to emerge from the tube. The fluoroscope consisted of an ordinary fluoroscopic screen set parallel with the line of vision. He made use of a mirror to reflect a shadow on the fluorescent screen, but his device was a hand fluoroscope, and, as such, was necessarily of limited use and fraught with all the dangers of exposure to the direct rays. Lewis Gregory Cole (2), of New York, in 1913 described a table in which he made use of a mirror, a fluorescent screen, and a stationary dark chamber. The table and dark chamber were placed against a lead-lined partition, back of which was placed a cabinet from which the table was operated. In the article descriptive of this table no mention was made of fluoroscopy outside of a dark room or cabinet. In Dr. Cole's device the operator was separated from the patient, which, of course, made it impossible for him to do manual palpation in a gastro-intestinal series, or manual manipulation in case of a fracture. With the Cole table it was necessary to adjust the patient to the screen, rather than the screen to the patient. In other words, Dr. Cole's screen was stationary and could be used only from one fixed point on the table, as the rest of the table was lead-lined beneath. For several months, I have been using in my office (a well lighted room), a daylight fluoroscopic device which has given me considerable satisfaction. I am not separated from the patient, can palpate while observing the shadow or can allow the surgeon to manipulate a fracture while observing the shadow. The fluoroscopic screen can be adjusted to the patient rather than the patient to the screen, as my device is beneath the table and can be moved lengthwise and crosswise with respect to the table. While the series of cases in which I have used this device is a comparatively small one, I feel that it is large enough to justify me in bringing the principle before the roentgenologists. I submit a drawing (Fig. 1) which will clearly bring out the idea, and will describe it in a brief way. Reduced to its simplest terms, this device consists of a freely movable lead-lined dark chamber, having a fluorescent screen placed on lead glass, backed by a colored plain glass of wood, which excludes all light from the chamber, and serves a s a roof for the same. In the bottom of the chamber is placed a mirror which is capable of being tilted to an angle, and this reflects the shadow from the screen. In the side of the cabinet facing the operator is a lead-lined glass window which may be as large as 8 × 10 for observation of the shadow.