Spatial filter

About: Spatial filter is a research topic. Over the lifetime, 6170 publications have been published within this topic receiving 100451 citations.

Method and system for electronic spatial filtering of spectral reflectometer optical signals

Abstract: A method for determining endpoint of plasma processing of a semiconductor wafer includes providing a light source, and providing a lens system to collimate and align light from the light source to an active surface of the semiconductor wafer. A plurality of light detector fibers are interleaved among light source fibers which transmit light from the light source to the lens system. Reflected light from the active surface of the semiconductor wafer is received by a plurality of light detector fibers and provided to an imaging spectrometer. The received reflected light is analyzed by the imaging spectrometer, and matched to a model optical signal. The matched optical signal is selected to determine endpoint or other state of the plasma processing.

Metallic grating spatial filter for directional beam forming antenna

Abstract: Sidelobe suppression and other beam transmission property manipulations in directional beam forming antennas is accomplished by means of a spatial filter The filter geometry consists of a plurality of metallic gratings separated by air or other low dielectric constant dielectric substance The filter is placed directly over the antenna radiating aperture and is encompassed by a tunnel structure of electromagnetic wave energy absorbing material The shunt susceptance characteristics of the metallic gratings together with the integrating spacing distances are synthesized in a manner that effects full transmission of beam power in a selected beam direction while offering substantial rejection of it in other directions

Time-domain correlator for spatial filtering in a pulsed energy system

Abstract: A pulse compression coded type pulsed energy system having timedomain correlation means permitting narrow-band processing of wide band receiver signals without comprising the data resolution limits thereof. Local oscillator injection means provides a coded periodic sampling signal at a local oscillator input of an intermediate frequency receiver, the sampling periodicity of which sampling signal is substantially less than the system pulse repetition interval and the coding of which sampling signal is a replica of that transmitted by the pulsed energy system. The time-phase of the sampling periodicity of the sampling signal is discretely progressively varied each pulse repetition interval. Data matrix storage means responsive to the variable time-phase sampling signals reconstructs a range trace signal of improved resolution, which may be further processed by radial extent logic to effect spatial filtering within system subpulse intervals.

Holographic transmission bandpass filter

Abstract: A narrow bandwidth bandpass filter having high transmission efficiency for the passband and excellent out-of-band attenuation employs a transmission holographic grating sandwiched between the oblique faces of a pair of right angle glass prisms. An incoming laser beam to be filtered is incident normal to one of the prism faces so as to intersect the holographic grating at about 45°. The grating frequency is such as to diffract light of the transmission wavelength through substantially 90° so that it exits the cube formed by the two prisms from the right angle face of the second prism. The out-of-band wavelengths of the incident beam are either transmitted unaffected through the grating or diffracted at a different angle than the light of the transmission wavelength. A spatial filter comprising a mask with a central aperture is supported a spaced distance from the output face of the cube so that diffracted light of the transmission wavelength passes through the aperture and the unwanted wavelengths, which are diffracted at different angles than the transmission wavelength, are blocked by the mask.

Method for determining a specific characteristic of fluid suspended particles

Abstract: A method for determining a specific characteristic of fluid suspended particles such as determining the total volume of particulate, as in stack gases. A laser beam is passed through the stack gases to produce diffraction patterns which are spatially filtered so that the total diffracted light flux passing through the filter is proportional to the total volume and hence the mass of the particles. A central opaque region is used on the filter to intercept the incident laser beam. The portion of diffracted light which is intercepted by that opaque region is compensated for by a region of enhanced transmission next to the center to restore response relating to the large particles. The spatial filter transmits a fraction of the diffracted light proportional to the reciprocal of the diffraction angle so that the total flux will be proportional to the cube of the diameter of the particulate and hence the particulate volume. When a long path is involved the particle information which is lost is compensated for by an enhanced transmission of the diffracted light from nearby small particles. Thus, in an outer region of the filter the transmission factor is held constant to provide the necessary compensation for the lost light flux.