Technical Data for the Arecibo Airglow and Lidar Instrumentation

A. Tilting-Filter Photometers:

2 available; Single channel; Bandwidth (3 dB) 0.3 to 1.0 nm (depends on choice of interference filter); Programmable filter tilt via stepping motors with 10^o tilt range or approximately 2.5 nm scan range; Field-of-view is variable between 0.25^o and 5.0^o by selecting field stops; Photomultiplier tube detection; Thermal control of filters and detectors; Pulse counting used; Calibration via ¹⁴C source; Radiant sensitivity depends on tube and filter configuration, but typically is about 300 (counts/sec) / (R/A).

B. Ebert-Fastie Spectrophotometer:

1 available; 1 meter focal length; Variable bandwidth between 0.02 and 1.0 nm using selectable slit widths; Programable wavelength scan via stepping motors with maximum scan range limited to 100 nm anywhere between roughly 300 and 900 nm; Variable field-of-view between 0.1^o and 9.0^o; Set of Corning order sorting filters; Set of spectral lamps for wavelength calibration; Thermal controlled photomultiplier tube detector; Pulse counting used; Tungsten and hydrogen lamp calibration sources used for the visible and ultraviolet part of the spectrum, respectively; Typical radiant sensitivity at 630 nm of ~25 (counts/sec) / (R/A).

C. Fabry-Perot Interferometers:

2 available, each with 1.2 meter focal lengths; 0.15 meter clear apertures; Etalon plates used are at lambda/150 and lambda/70; Reflectivity typically 85% at 630 nm; Typical bandwidth of 0.001 nm; Free spectral range 0.01 nm; Wavelength change via pressure scanning using pistons and choice of scanning gas of Ar, CO₂, or SF₆; Field-of-view depends on choice of aperture size, but is typically 0.25^o for 630 nm observations; He-Ne frequency stabilized laser for linewidth calibration; Thermal control of etalon and prefilter; Spectral line sensitivity of ~2 counts/sec/R.

D. Doppler Rayleigh Lidar:

1 available; Nd:YAG based laser transmitter; 24 W average power (100 MW peak power) at 532 nm; Additional output at 1064 nm fundamental (currently 355 nm is not available); 6 ns pulse width; 40 Hz operation; 80 cm diameter Cassegrain telescope receiver; Fully pointable (but generally aircraft restricted to within 45^o of zenith; Electronic gated photomultiplier tube detection with low-altitude chopper; Data collection is based on an EG&G multichannel, scaler-averager capable of 5 ns range sampling (or 75 cm range resolution), but is generally programed for a more course range sampling.

E. Resonance Fluorescence Lidars:

Essentially 2 are available (Alexandrite-laser based, and Dye-laser based). The Alexandrite laser transmitter can be set between 720 and 800 nm with doubled frequency output between 360 and 400 nm; A one-meter Raman cell is available for additional frequency shifting; 3 W average power (0.5 MW peak power) at 770 nm; 200 ns pulse width; 28 Hz operation. The Dye laser transmitter is tunable between about 300 nm and 800 nm depending on the dye/solvent used, and the use of sets of doubling and mixing crystals; 4 W average power (20 MW peak) at 589 nm; 5 ns pulse width; 40 Hz operation; dual-wavelength capability.

Both lidar systems employ 80 cm diameter, pointable Cassagrain telescopes and gated photomultiplier tube detectors with low-altitude choppers. Data collection is based on EG&G multichannel, scaler-averagers capable of 5 ns range sampling (or 75 cm range resolution), but these are generally programed for a more course sampling, typically at 75 to 150 m range resolution.

F. Airglow Mirror Systems:

4 available; Dual axes (azimuth and elevation); Complete programmable control of movement using stepping motors; 10 steps per degree; First surface mirrors mounted under plexiglass protective domes.

G. Photomultiplier Tubes:

A set of Hamamatsu R943-02, RCA 31034A-02, EMI 9658AR, EMI 9558AR, and EMI 9863B-350 tubes are available for detectors.

H. Data Acquisition and Control System:

Airglow: DEC Micro PDP-11 computer with 11/83 processor, 2.0 Mb memory, 159 Mb disk, 95 Mb, 0.5" cassette tape subsystem for backups, dual 5.25" 400 Kb floppy disks, linked via Ethernet AO Network; VT-240 graphics terminal; LA-50 printer; Micro-RSX multitasking, real-time operating system with capability for automatic reboot and program restart upon detection of a fault or program crash. Camac interface to instruments, including stepping motor controllers, pulse counters, and digital and analog I/O, Moseley X-Y plotter, and Linear dual channel strip chart recorder. (Despite its antiquity, the Micro-PDP has many inherent capabilities for the type of flexible data acquisition for which it is used. However, we plan to replace this computer later this year with one based on a PC.)

Lidar: Standard PC 486s and Pentium computers running Windows 3.1.1 and/or Windows 95/98 directly interfaced to EG&G multichannel scaler-averagers; PCs are networked to AO computers. Diagnostic instruments include a Burleigh wavemeter, Scientec and Newport power meters and a Spiricon camera.

Craig Tepley -- ctepley@naic.edu
Revised -- 30 August 2000