Abstract: A laser having a stabilized external passive cavity is disclosed, with stabilization being effected by modulation of an external mirror positioned along the laser axis. The laser system includes first, second and third spaced mirrors with the second mirror being an output coupler positioned between the first and third mirrors so that an active cavity is defined between the first and second mirrors and a passive cavity is defined between the second and third mirrors. The active cavity feeds, or pumps, the passive cavity which is stabilized by modulation of the third mirror by movement along the laser axis by linear oscillation to Doppler shift the reflected waves within the passive cavity and thereby produce frequencies that do not interfere with the stable modes of the active cavity.

Abstract: An aerosol sampling device and method are disclosed having improved sample flow characteristics. Sample flowing through an inlet nozzle is heated prior to discharge from the nozzle toward a measurement area to maintain sample flow more nearly laminar by compensating for the adiabatic cooling that occurs due to acceleration of flow through the nozzle. In addition, heating of the sample flow prevents condensation which can result with ambient air having a relative humidity of fifty percent. An optical particle measuring apparatus is shown having a generator for providing a laser beam, the path of which is through a measurement area, and an inlet nozzle through which aerosol sample is injected into the measurement area, after heating in accordance with this invention, to allow operation of the laser at a relatively high Q by reducing non-laminar flow characteristics.

Abstract: Method and apparatus for orienting and measuring fibrous particles by conducting longitudinally oriented fibrous particles through a beam of radiation and measuring the radiation scattered in a direction aligned with the length of such particle and, independently, also measuring the amount of radiation scattered transverse to the length of the particle. Preferably, the measurements are accomplished utilizing a sensor having an inactive center portion substantially corresponding to the area of undisturbed beam of radiation, a first photosensitive area in a portion of the sensor aligned with the length of the particles, and a second, independent photosensitive area transverse to the length of the particle. Signals generated by the two photosensitive areas are added to determine the size of the particles, and the ratio between the signals is established to determine the aspect ratio of the particle.

Abstract: Method and apparatus for establishing a valid sample volume in a beam of radiation, wherein a sample stream is introduced substantially transversely to the radiation beam, an optical system is configured to produce images on first and second image planes, the two planes preferably being perpendicular to one another and established by means of a beam splitter, first and second photosensors being positioned in the image planes, the first photosensor having greater optical and an electronic gain and a masked portion, and the second photosensor being either unmasked or having masked portions corresponding generally to the unmasked portions of the first photosensor, the first photosensor being connected to comparator means and the second photosensor also being connected to the comparator means which accepts data only when the signal from second photosensor is of a greater magnitude than the signal from the first photosensor, whereby images on the photosensors from points outside the selected sample volume will be

Abstract: Two-dimensional data may be acquired at extremely high rates by means of a linear sensor array, and ganged shift registers with each sensor associated with at least one shift register. The state of each sensor is sampled periodically in accord with a selected, relatively high clock frequency and each sampling is sequentially recorded in the shift register associated with a specific sensor. A first dimension is provided by the linear nature of the sensor array and the second dimension is supplied by the sampling clock frequency as a subject moves past the sensor array. In a more advanced embodiment, the sampling operates only during the occurrence of an event and data is cyclically recorded in one group of shift registers at a rapid rate while previous data is unloaded from an alternative group of shift registers at a conventional rate.