Signal beam

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

Experimental comparison of autodyne and heterodyne laser interferometry using an Nd:YVO₄ microchip laser.

Abstract: Using an Nd:YVO4 microchip laser with a relaxation frequency in the megahertz range, we have experimentally compared a heterodyne interferometer based on a Michelson configuration with an autodyne interferometer based on the laser optical feedback imaging (LOFI) method regarding their signal-to-noise ratios. In the heterodyne configuration, the beating between the reference beam and the signal beam is realized outside the laser cavity, while in the autodyne configuration, the wave beating takes place inside the laser cavity, and the relaxation oscillations of the laser intensity then play an important part. For a given laser output power, object under investigation, and detection noise level, we have determined the amplification gain of the LOFI interferometer compared to the heterodyne interferometer. LOFI interferometry is demonstrated to show higher performance than heterodyne interferometry for a wide range of laser powers and detection levels of noise. The experimental results are in good agreement with the theoretical predictions.

Optical phase adder

Abstract: A photosensitive element 46 absorbs at least a portion of an incident write beam 40, causing a spatially varying electric field to be applied across a layer of a ferroelectric liquid crystal (FLC) 48, thereby forming a pattern of local polarizations corresponding to the spatially varying electric field. In one embodiment, a signal beam is modulated with a phase variation characteristic of a particular aberrator. The signal beam is then combined with a substantially plane wave reference beam to form interference fringes. These interference fringes are directed as a write beam onto photosensitive layer 46, forming a hologram in FLC layer 48 which can be read optically. An incident beam of light can be diffracted by a hologram formed in the FLC layer, thereby modulating the incident beam of light with the phase variations comprising the hologram. In a preferred embodiment, the phase characteristics of an aberrator 76 are recorded as a hologram in an optically addressed spatial light modulator 10 and that hologram may be used to remove aberrations from an incident probe beam 83 that was modulated by aberrator 76. In a preferred embodiment, a large portion of the incident probe beam 82 intensity will be diffracted into a first order diffraction mode. This corrected probe beam 84 will be a substantially image corrected beam of light.

Sub-parts-per-quadrillion-level graphite furnace atomic absorption spectrophotometry based on laser wave mixing.

Abstract: Nonlinear laser wave mixing in a common graphite furnace atomizer is presented as a zeptomole-level, sub-Doppler, high-resolution atomic absorption spectrophotometric method. A nonplanar three-dimensional wave-mixing optical setup is used to generate the signal beam in its own space. Signal collection is efficient and convenient using a template-based optical alignment. The graphite furnace atomizer offers advantages including fast and convenient introduction of solid, liquid, or gas analytes, clean atomization environment, and minimum background noise. Taking advantage of the unique features of the wave-mixing optical method and those of the graphite furnace atomizer, one can obtain both excellent spectral resolution and detection sensitivity. A preliminary concentration detection limit of 0.07 parts-per-quadrillion and a preliminary mass detection limit of 0.7 ag or 8 zmol are determined for rubidium using a compact laser diode as the excitation source.

Recording and reproducing method

Abstract: A hologram recording method for forming a light interference pattern in a hologram recording medium to record information thereon. The method includes a step of interfering with a reference beam a signal beam spatially modulated by an information pattern which carries the information to generate interfered beams. The method includes a step of executing a recording sequence a plurality of times, the recording sequence including steps of irradiating the interfered beams onto a recording surface of the hologram recording medium to form a group of a plurality of holograms each corresponding to the information pattern. The method includes a step of completing the recording sequence. Different modulation conditions are set for at least one of the signal beam and the reference beam in one recording sequence and the subsequent recording sequence immediately after the one recording sequence.

Dark and bright photovoltaic spatial solitons in photorefractive crystals with positive refractive-index perturbation

Abstract: We have demonstrated, for what is believed to be the first time, that in a photorefractive crystal with positive refractive-index perturbation a two-dimensional dark or bright photovoltaic spatial soliton can be formed in the same crystal by a signal beam and a background beam of different wavelengths. We discuss the conditions on the effective Glass constants and the absorption coefficients of the background and signal beams in determining the formation of the spatial soliton.