ABSTRACT
In proximity focused electrostatic image tube; spatial resolution is a strong function of the cathode flatness.Topographic irregularities of the cathode surface establish transverse electric fields near the cathode.The fields impart a component of transverse momentum to the emitted electron, which, in turn,degrades the spatial resolution characteristic of the system. Calculations based on a simple model of a corrugated cathode show that, under a typical set of operating conditions, the point at which loss of resolution becomes considerable is 60 cycles/mm for a bump height of 0.2 microm and a bump period of 1 microm. For the resolution to be comparable to that predicted for a perfectly flat GaAs negative electron affinity (NEA) cathode, which is 160 cycles/mm, the bump period must be 0.1 microm, and its height must be 0.02 microm. Such small bumps represent a relatively smooth surface. Observations of surface irregularities on related NEA surfaces indicate that the bump period and height are about 1.0 micro and 0.2-0.5 microm, respectively, so that the spatial resolution in these cases is limited by the deviation from flatness as opposed to being limited by the finite random velocities of the emitted photoelectrons.
ABSTRACT
We have observed some of the absorption lines from the molecules (12)CO(2) and (13)CO(2)in the 1.6-µm spectral region with the use of specially fabricated single-mode InGaAsP distributed-feedback semiconductor diode lasers. Using a 23.6-m-long multipass absorption cell in combination with radio-frequency modulation and detection techniques, we measured the (12)CO(2):(13)CO(2) isotopic ratio of two specific lines at 6253.73 and 6253.90 cm(-1) with sufficient precision for diagnostic medical tests that analyze CO(2) on human breath.
ABSTRACT
An open path diode laser sensor was constructed with near-infrared diode lasers and two-tone frequency-modulation spectroscopy. The sensor incorporates several novel features (such as digital signal-processing algorithms, a computerized line-locking routine, and discontinuous wavelength scanning) that are important in a field instrument. The sensor was used to monitor oxygen, water, and carbon dioxide in the near-infrared spectral range. For oxygen, an absorbance detection sensitivity of 2 × 10(-6) in a 10-Hz bandwidth was demonstrated with a GaALAs laser at 760.56 nm. The stability of the sensor was 0.1% over a period of 10 h when an absorbance of 6 × 10(-3) was monitored.
ABSTRACT
We review the recent progress of electrically injected and optically pumped mid-IR lasers based on antimonide quantum wells with the type II W configuration. W quantum-well diodes have achieved cw operation up to 195 K at lambda = 3.25 mum. Optically pumped devices that employ the diamond pressure bond heat sink have reached 290 K at 3 mum and 210 K at 6 mum. Pulsed power conversion efficiencies of up to 7% at 220 K have been attained by use of an optical pumping injection cavity approach, in which an etalon cavity for the pump beam significantly enhances its absorptance. The angled-grating distributed-feedback configuration has been used to obtain near-diffraction-limited output for an optical pumping stripe width of 50 mum.