Signal beam

About: Signal beam is a research topic. Over the lifetime, 1881 publications have been published within this topic receiving 20717 citations.

Optically actuated optical switch apparatus and methods

Abstract: A switch capable of switching an optical beam without employing conventional mechanical, electrical, or optical devices The switch includes a switching medium which may be a solid, liquid, gas, or supercritical gas A signal or switched beam is directed into and through the switching medium In order to change the path of the signal beam as it travels through the switching medium, the refractive index of the switching medium is changed This change in refractive index is caused by a control beam selectively directed into the switching medium The control beam produces a transient refractive index gradient within the switching medium This gradient may be a thermal gradient and may constitute a thermal lens The switch of the current invention is capable of picosecond response times and may serve as a fiber optics communications switch as well as an element in an optical computer

Gun shaped remote control unit for a television

Abstract: A universal remote control unit for changing television channels is shaped like a gun to allow a viewer to point the gun at a television set, and shoot the channel to change the program. The unit is gun shaped having a barrel with a muzzle end containing an infrared beam emitter to produce a signal beam to engage an infrared beam receiver of a television set and provide channel selection. A hand grip portion has a trigger which operates a channel selection switch to produce a signal beam from the infrared emitter to change the channel. A channel direction switch selects whether the channel change should be up or down, and a power source is provided for powering the controls and the light beam emitter. In another embodiment a light beam emitter and a sound effect emitter are included in the gun.

InGaAs multiple quantum well modulating retro-reflector for free-space optical communications

Abstract: Modulating retro-reflectors provide means for free space optical communication without the need for a laser, telescope or pointer tracker on one end of the link. These systems work by coupling a retro-reflector with an electro- optic shutter. The modulating retro-reflector is then interrogated by a cw laser beam from a conventional optical communications system and returns a modulated signal beam to the interrogator. Over the last few years the Naval Research Laboratory has developed modulating retro-reflector based on corner cubes and large area Transmissive InGaAs multiple quantum well modulators. These devices can allow optical links at speeds up to about 10 Mbps. We will discuss the critical performance characteristics of such systems including modulating rate, power consumption, optical contrast ratio and operating wavelength. In addition a new modulating retro-reflector architecture based upon cat s eye retroreflectors will be discussed. This architecture has the possibility for data rates of hundreds of megabits per second at power consumptions below 100 mW.

CARS spectral fitting with multiple resonant species using sparse libraries

Abstract: The dual pump CARS technique is often used in the study of turbulent flames. Fast and accurate algorithms are needed for fitting dual-pump CARS spectra for temperature and multiple chemical species. This paper describes the development of such an algorithm. The algorithm employs sparse libraries, whose size grows more slowly with number of species than a conventional library. The method was demonstrated by fitting synthetic "experimental" spectra containing 4 resonant species (N2, O2, H2 and CO2), both with noise and without it, and by fitting experimental spectra from a H2-air flame produced by a Hencken burner. In both studies, weighted least squares fitting of signal, as opposed to least squares fitting signal or square-root signal, was shown to produce the least random error and minimize bias error in the fitted parameters. I. Introduction Coherent anti-Stokes Raman spectroscopy (CARS) is a non-linear spectroscopic technique in which three laser beams, two pump beams and a Stokes beam, are focused and crossed at their focal point, and a fourth signal laser beam is generated at the intersection through a four-wave mixing process. Resonances associated with Raman active molecular rotational-vibrational transitions strengthen the CARS signal in a manner dependent on gas composition and temperature. The wavelength of excitation or "Raman shift" corresponds to the difference in energy between a pump beam and a Stokes beam (longer wavelength) photon. In the broadband CARS technique one of the laser beams, the Stokes beam, is spectrally broad whereas the other pump beams are spectrally narrow, and this enables multiple resonances to be excited. The signal beam is spectrally broad and carries with it the spectral signature of the gases present (over some range of wavelengths). This signal beam is dispersed by a spectrometer and spectra are compared to analytical models to obtain information on composition and temperature. In the dual-pump CARS technique, originally developed by Robert Lucht and coworkers, 1,2 the two pump beams are at different wavelengths and two different ranges of Raman shift may be accessed. In recent years, efforts have been made to utilize the CARS technique to obtain experimental data for development and validation of computational models of supersonic combustion. Data sets have been acquired in a hydrogen-fueled supersonic combustor using the CARS technique 3 to measure temperature, and the dual-pump CARS technique has been used to measure temperature and composition; 4 in Ref. 3 the resonant species was N2 and in Ref. 4 they were N2, O2, and H2. Both mean flow and turbulence statistics (variances and covariances) were derived from the data, although the uncertainty in the latter was high due both to instrument error and to the small number of measurements on which to base the statistics. More recently, data have been acquired in a hydrogen- combustion heated supersonic coaxial jet with the intent to obtain turbulence statistics of lower uncertainty. 5 These efforts required analysis of large numbers of experimental spectra containing up to three different species. Analysis of dual-pump CARS experimental spectra is typically performed with the Sandia CARSFT code as modified by Lucht 1,2,6 and O'Byrne. 4 The CARSFT code is able to accurately compute spectra for a range of molecular species and, in the fitting mode, to read an experimental spectrum and fit it to a theoretical spectrum by repeatedly computing spectra and minimizing the residual between the theoretical and experimental spectra. This fitting process becomes very slow when the number of molecular species increases, due to a large spectral range, many energy level transitions, and a large number of iterations. Additionally, when fitting multiple variables, CARSFT has problems in finding a global minimum, sometimes returning a result dependent upon the initial guess. At NASA Langley, with the exception of Tedder et al., 5 CARS data has usually been fitted using libraries of spectra. 3,4 Libraries are computed ahead of time using CARSFT. Theoretical spectra are then interpolated from the library rather than being calculated from scratch. However, conventional library size scales to the power of the number of parameters varied (temperature plus resonant chemical species) and tends to become uneconomically

Multimodal coherent anti-Stokes Raman spectroscopic imaging with a fiber optical parametric oscillator.

Abstract: We report on multimodal coherent anti-Stokes Raman scattering (CARS) imaging with a source composed of a femtosecond fiber laser and a photonic crystal fiber (PCF)-based optical parametric oscillator (FOPO). By switching between two PCFs with different zero dispersion wavelengths, a tunable signal beam from the FOPO covering the range from 840 to 930 nm was produced. By combining the femtosecond fiber laser and the FOPO output, simultaneous CARS imaging of a myelin sheath and two-photon excitation fluorescence imaging of a labeled axons in rat spinal cord have been demonstrated at the speed of 20 μs per pixel.