Light Attenuators Research Articles

H Lyman a transmittance of thin C and Si/C foils for keV particle detectors

Interests in the use of thin foils as light attenuators and signal generators for energetic particle instruments in space have led to the measurement of transmittance of thin C and Si/C foils at 1216 Å, where the most intense and ubiquitous photons in the solar system reside. Our results indicate that 1) a transmittance of < 7 × 10 −4 can be achieved with 7 μg/cm 2 Si on 1.7 μg/cm 2 C; 2) Si/C composite foil with a thin carbon layer is more effective in blocking UV radiation and less likely to change its particle energy threshold under ion-irradiation than a pure carbon foil of identical areal density prior to exposure to ions; and 3) transmittance of Si/C foils of known Si and C thicknesses cannot be accurately predicted, but must be measured.

Nonlinear dispersion effects in the low-noise properties of squeezed light in transmission chains formed from nonlinear alternating attenuators and amplifiers

An idealized model of an optical communication link in which identical sections of nonlinear attenuating fiber alternate with identical optical amplifiers is considered. Signal-to-noise ratios of chains of these elements for input squeezed and coherent light have been numerically evaluated, taking into account the deleterious effects due to nonlinear dispersion. It has been previously shown that input squeezed light and nonlinear attenuators improve the signal-to-noise ratios with respect to coherent inputs and linear chains. It is shown here that nonlinear dispersion degrades the signal-to-noise ratios, but the coherent input is more appreciably degraded than the squeezed input.

Low-noise properties of squeezed light in transmission chains formed from nonlinear alternating attenuators and amplifiers

An idealized model of an optical communication link in which identical sections of nonlinear attenuating fiber alternate with identical amplifiers is considered. Signal-to-noise ratios of chains of these elements for input squeezed and coherent light have been numerically evaluated. It is found that input squeezed light and nonlinear attenuators improve the signal-to-noise ratios with respect to coherent inputs and linear chains. In the case of three-photon attenuators, the noise and signal-to-noise ratio remain practically constant from certain elements of the chain. Moreover, the influence of the attenuation coefficient and the input mean photon number on the signal-to-noise ratios was considered, as well as chains with nonlinear amplifiers and chains in which the amplifier gain does not exactly compensate for the fiber attenuation.

Etched Wire Screens as Variable Light Attenuators

In the course of infrared studies on dense materials with double-beam instruments, it is frequently necessary to attenuate the reference beam in order to be able to record the spectrum. Also, in some studies, particularly with the interaction of gas with a solid, the sample transmission can vary with experimental conditions, so that continual adjustment of reference beam intensity must be made. Such adjustments are very inconvenient to make with wire mesh screens or slotted shutters because these produce a step-by-step attenuation. Continuous attenuation is desirable for such purposes. Some continuously-variable attenuators made of tilting vanes (1) or wire screens (2) have been described. Such devices are useful but have the disadvantages of large size and non-linearity of attenuation. The rotary motion must be controlled precisely and, because of the rotation of such a device, a substantial fraction of the reference beam space is taken up so that large compensating cells cannot be accommodated.

Use of Wire Screens as Variable Light Attenuators

Spectrochemical procedures occasionally call for the use of a wire screen to reduce the intensity of a light source. Sometimes the screen is specified as having a given optical transmittance; more often it is described as being of a given mesh. Such screens are presumed to be used at normal incidence and when used as an attenuator are known to be optically stable with respect to time and ideally neutral with respect to wavelength (1).