To improve the performance of GaAs NEA photocathodes, an exponential-doping structure GaAs material has been put forward, in which from the GaAs bulk-to-surface doping concentration is distributed exponentially from high to low. We apply this exponential-doping GaAs structure to the transmission-mode GaAs photocathodes. This sample was grown on the high quality
p-type Be-doped GaAs (100) substrate by MBE. We have calculated the band-bending energy in exponential-doping GaAs emission-layer, and the total band-bending energy is 59 meV which helps to improve the photoexcited electrons movement towards surface for the thin epilayer. The integrated sensitivity of the exponential-doping GaAs photocathode samples reaches 1547uA/lm.
Because of its high photoemission performance, NEA photocathode has been developed rapidly and used widely in the recent several decades after it was found. In view of the problems existing in the research and producing of NEA photocathode, the study of property evaluation of NEA photocathode has been carried out in this paper. The spectral response decay of NEA photocathode has been measured, which provides valuable data for the stability research. The factors that influence the quantum yield of NEA photocathode are expounded. The characteristic parameters of NEA photocathode and the way of realizing property evaluation are introduced. The reflective GaAs samples are activated and evaluated by the activation and property evaluation system. The spectral response of NEA photocathode is measured on-line when it is being activated. The activation technique is analyzed and discussed combining with technology of XPS analysis. The property evaluation of NEA photocathode is realized. The properties of different NEA photocathode are compared. The problems in the research on NEA photocathode are pointed out.
We have designed and built two versions of a space-qualifiable, single-frequency Nd:YAG laser. Our approach to frequency stabilization of the seeded oscillator is a variation of the “ramp and fire” technique. In this design, the length of the pulsed laser cavity is periodically varied until a resonance with the seed laser is optically detected. At that point the pulsed laser is fired, ensuring that it is in resonance with the seed laser. For one of the lasers the resulting single frequency pulses are amplified and frequency tripled. This system operates at 50 Hz and provides over 50 mJ/pulse of single-frequency 355 nm output. It has been integrated into the GLOW (Goddard Lidar Observatory for Winds) mobile Doppler lidar system for field testing. The second laser is a 20o Hz oscillator only system that is frequency doubled for use in the High Spectral Resolution Lidar (HSRL) system being built at NASA Langley Research Center. It provides 4 mJ of single-frequency 532 nm output that has a spectral purity of >10,000. In this paper we describe the design details, environmental testing, and integration of these lasers into their respective lidar systems.
The Goddard Lidar Observatory for Wind (GLOW) has participated three field campaigns since Sept. 2000. Near 300 hours of wind measurement under a wide variety of conditions including day and night operation, high and low altitude, line of sight and horizontal winds, have been obtained from the GroundWinds intercomparison, Harlie-GLOW intercomparison ( HARGLO) and the International H2O Project (IHOP) field campaigns. The GLOW system has demonstrated the capability to atmospheric wind from ground up to 30 km with an accuracy of 0.4-6m/s.
In this paper we present a detailed analysis of the performance of the Goddard Lidar Observatory for Winds (GLOW) Doppler lidar. GLOW is a mobile direct detection Doppler lidar system which uses the double edge technique to measure the Doppler shift of the molecular backscattered laser signal at a wavelength of 355 nm. The lidar has been used in several recent field experiments to measure wind profiles from the surface into the lower stratosphere. Simulations of detected signal levels predicted using a realistic instrument model and representative atmospheric model will be presented and compared with range resolved signals detected with the photon counting data acquisition system. A detailed analysis of wind errors observed with the system will also be reported. The analysis begins by propagating ideal shot noise limited errors through the analysis algorithms used to calculate winds. The resulting shot noise limited errors are compared with statistical standard deviations obtained by averaging multiple independent wind profiles taken at various temporal and spatial sampling scales. An assessment of other instrumental and atmospheric effects contributing to the wind error will also be given.
The Goddard Lidar Observatory for Winds (GLOW) is a mobile Doppler lidar system which uses direct detection Doppler lidar techniques to measure wind profiles from the surface into the lower stratosphere. GLOW is intended to be used as a field deployable system for studying atmospheric dynamics and transport and can also serve as a testbed to evaluate candidate technologies developed for use in future spaceborne systems. In September of 2000 GLOW particpated in a three week intercomparison experiment at the GroundWinds facility in North Glen, NH. More than 50 hours of line-of-sight wind profile data were obtained in a wide variety of conditions including both day and night operation. Typical clear air lidar wind profiles extended to altitudes of 20 km with a 1 km vertical resolution and 1 minute averaging. A description of the mobile system is presented along with the examples of lidar wind profiles obtained with the Goddard system during the New Hampshire experiment.
GLOW (Goddard Lidar Observatory for Winds) is a mobile Doppler lidar system which uses direct detection Doppler lidar techniques to measure wind profiles from the surface intO the lower stratosphere. The system is contained in a modified van to allow deployment in field operations. The lidar system uses a Nd:YAG laser transmitter to measure winds using either aerosol backscatter at 1064 nm or molecular backscatter at 355 nm. The receiver telescope is a 45 cm Dall-Kirkham which is fiber coupled to separate Doppler receivers, one optimized for the aerosol backscatter wind measurement and another optimized for the molecular backscatter wind measurement. The receivers are implementations of the 'double edge' technique and use high spectral resolution Fabry-Perot etalons to measure the Doppler shift. A 45 cm aperture azimuth-overelevation scanner is mounted on the roof of the van to allow full sky access and a variety of scanning options. GLOW is intended to be used as a deployable field system for studying atmospheric dynamics and transport and can also serve as a testbed to evaluate candidate technologies developed for use in future spaceborne systems. In addition, it can be used for calibration/validation activities following launch of spaceborne wind lidar systems. A description of the mobile system is presented along with the examples of lidar wind profiles obtained with the system.
A novel ultra-narrow Na Faraday vapor filter was developed and is in use with our Na temperature lidar system for daytime measurements of the atmospheric temperature near the mesopause. The first 34 hour continuous observation was carried out from 1 pm, Oct. 10 to 11 pm Oct. 12, 1995, terminated by clouds. Signal to background ratio at high noon was about 15 at Na D2a peak frequency.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.