Electron beam pattern generators are nowadays used extensively for the production of masks and for direct writing on wafers. For obvious reasons electron beam pattern generators are optimized for integrated circuit fabrication. However there is also considerable potential for the use of electron beam lithography in other areas. In this paper recent trends in the development of electron beam pattern generators are described and the problems encountered in the application of electron beam machines in other areas e.g. integrat-ed optics are discussed.

Gas lasers have shown to be capable of delivering tens of terrawatt aspeak power or tens of kilowatt as average power. The efficiencies of most high power gas lasers are relatively high compared with other types of lasers. For instance molecular lasers, oscilating on low lying vibrational levels, and excimer lasers may have intrinsic efficiencies above 10%.The wavelengths of these gas lasers cover the range from the far infrared to the ultra-violet region, say from 12000 to 193 nm. The most important properties are the scalability, optical homogeneity of the excited medium, and the relatively low price per watt of output power. The disadvantages may be the large size of the systems and the relatively narrow line width with limited tunability compared with solid state systems producing the same peak power.

A small backscatter lidar for measurements from the Spacelab-facility is proposed. The purpose of this instrument is to explore the measurement capabilities of a spaceborne lidar and to assess the performance potential of future operational instruments. A first flight opportunity may arise with the German D2-mission in the early 1990's.

The difficulties encountered in using conventional formulations of polarised scattering are overcome by employing a target decomposition theorem based on the concept of a target coherency matrix. To illustrate the classification potential of this new formalism, two important scattering problems are considered; the scattering of light by a cloud of randomly oriented anisotropic particles and the reflection of light from a rough surface. In both cases, emphasis is placed on the polarisation properties of the scattered light and experimental results are presented to illustrate the potential of the new formalism for a classification of surfaces and particle clouds.

We present the design of a high power, single longitudinal mode and near diffraction limited Q-switched Alexandrite laser. Different experimental solutions, suitable for spaceborne LIDAR applications are examined and critically discussed.

We present a comparative experimental investigation of the performance of a number of different frequency selective optical configurations used for line-narrowing of low-gain, solid-state lasers operated in prelasing Q-switched regime. This study has been carried out by paying particular attention to relevant optical problems for the realization of reliable single-mode, tunable, spaceborne, vibronic lasers.

This paper describes a ground-based Raman lidar for the measurement of vertical concentration profiles of tropospheric water vapor. The system will also be used to assess the feasibility of carbon dioxide profile determination. The main components are a xenon chloride excimer laser, reflective 0.4-m transmitter and 0.8-m receiver optics, liquid edge filter for suppression of the Rayleigh and Mie scattered photons, and an echelle grating polychromator for wavelength separation. The data acquisition is done by a fast multichannel scaler. The apparatus is described, and first moisture measurements up to a vertical distance of 3 km taken in less than 2 minutes with a spatial resolution of 120 m are presented.

The optical design of the pressure modulator infrared radiometer (PMIRR) is described. This limb and nadir scanning instrument will be used for remote sounding of the Martian atmosphere. To do this, the instrument has two pressure modulator cells and nine channels distributed over the wavelength range 0.3 to 50 microns.

The European weather forecasters expressed their needs for the Second Generation Meteorological satellites in the Avignon workshop, june 1984. Two optical functions are required : imaging and atmos-pheric sounding with the following main features: - imagery : notably improved from present Meteosat in terms of spatial and radiometric resolution, number of channels, repetitivity over Europe. - vertical atmospheric sounding : this new mission, performed simultaneously with the imagery, differs from the U.S. sounding mission for the future meteorological satellites (GOES, I, J, K) by a notably shorter measurement time. The requirements are analysed and their impacts on the instruments' design are discussed.

This paper describes the Improved Stratospheric and Mesospheric Sounder (ISAMS) which is one of ten experiments due to be launched on the NASA Upper Atmosphere Research Satellite. ISAMS is an eight channel infra-red radiometer utilising pressure modulator radiometry which has been used successfully on Pioneer and Nimbus experiments. The detectors operate at a temperature of 80°K which is achieved by specially developed Stirling cycle coolers. The emphasis of the paper will be on the optical system which must meet the very tight requirements on field of view and pointing which come from the limb viewing approach. Also considered will be the structural integrity needed to overcome motional chopping, thermal problems associated with the optical design and the laboratory testing needed to verify the performance.

An Astrometric Telescope Facility (ATF) for planetary detection is being studied as a potential Space Station initial operating capability payload. The primary science objective of this mission is the detection and study of planetary systems around other stars. In addition, the facility will be capable of other astrometric measurements such as stellar motions of other galaxies and highly precise direct measurement of stellar distances within the Milky Way Galaxy. This paper summarizes the results of a recently completed ATF preliminary systems definition study. Results of this study indicate that the preliminary concept for the facility is fully capable of meeting the science objectives without the development of any new technologies. This preliminary systems study started with the following basic assumptions: 1) the facility will be placed in orbit by a single Shuttle launch, 2) the Space Station will provide a coarse pointing system , electrical power, communications, assembly and checkout, maintenance and refurbishment services, and 3) the facility will be operated from a ground facility. With these assumptions and the science performance requirements a preliminary "strawman" facility was designed. The strawman facility design with a prime-focus telescope of 1.25-m aperture, f-ratio of 13 and a single prime-focus instrument was chosen to minimize random and systemmatic errors. Total facility mass is 5100 kg and overall dimensions are 1.85-m diam by 21.5-m long. A simple straightforward operations approach has been developed for ATF. A real-time facility control is not normally required, but does maintain a near real-time ground monitoring capability for facility and science data stream on a full-time basis. Facility observational sequences are normally loaded once a week. In addition, the preliminary system is designed to be fail-safe and single-fault tolerant. Routine interactions by the Space Station crew with ATF will not be necessary, but onboard controls are provided for crew override as required for emergencies and maintenance.

An integrated focal plane star sensor based on a four-quadrant detector was designed and developed for operation from ambient down to cryogenic temperature. One of the first applications of this system will be the fine pointing of the Infrared Space Observer (ISO) telescope, therefore the performance was optimized for operations around 2K. The sensor is constituted of a small sensitive head, operating at cryogenic temperature with very low power consumption, and of a processing electronics working in the typical temperature range for space electronics. A breadboard was reliazed and successfully tested both at ambient temperature (with reduced accuracy) and at 20K. The accuracy referred to the ISO optical system, was measured to be better than 1 arcsec.

Pronaos, a two metre balloonborne submillimetre telescope, supported by CNES and designed by a French collaboration between CNRS institutes and CNES-CST is presented. This project is now approved and in a preliminary definition phase B. It is intended to provide a facility for long duration flights (more than 20 hours) for photometry and spectroscopy in the spectral range 80 micrometres to 1.5 millimetre. Two focal plane instrumentations are considered : 1) a multiband photometre device using He3 cooled bolometres and He4 cooled filters. 2) a submillimetre heterodyne spectrometre. The two-metre Cassegrain telescope, with a lightweight primary mirror has an equivalent focal ratio F/10. The telescope is pointed (accuracy of 5"rms) with a two stages stabilisation having a two axis sys-tem : 1) the azimuth orientation of the gondola provides from the decoupling with the balloon (ac-curacy of a few arc-minutes) and 2) an elevation/ cross-elevation gimbal.

This paper describes the development and application of a novel fibre optic based RF signal processing system (FOSPAN*). The system is based upon recirculating delay line techniques and offers significant advantages over conventional digital techniques.

In recent years, a new class of instrument has been emerging for Earth and planetary remote sensing applications.1,2 Most often referred to as imaging spectrometers, or sometimes mapping spectrometers, these new instruments are of increasing interest because of their capability to perform direct identification of surface materials through their spectral signatures. This paper describes some of the system design and technology tradeoffs associated with the development of such instruments and gives design examples for both Earth and planetary applications.

This paper discusses the optical design and performance of the Shuttle Imaging Spectrometer Experiment (SISEX) optical system, which is being planned for the next generation of Earth remote sensing instruments. This optical system represents a new approach to remote sensing in which wide-field optics, dispersing elements, and area detector arrays are used in place of mechanical scanners, filters, and discrete detector elements or linear arrays. While the SISEX optical system is designed specifically for flight on Shuttle, the same optical approach is being used in the design of other remote sensing instruments, such as the High Resolution Imaging Spectrometer, which is expected to fly on the Earth Observing System.

This paper concerns an original design for a spectro-imager, in which spectral analysis is performed by interferometry, with the necessary path difference being obtained as a direct result of the apparent displacement of the source as seen from the satellite while orbiting. Descriptions will be given of the bread-board model used to determine the feasibility of the project, and of the transportable spectro-imager (SIT) currently being produced at Aerospatiale Cannes (France).

VEGETATION is one payload on the earth-observation satellite SPOT 4, launch-scheduled in 1992. It is developed, assembled and tested by AEROSPATIALE, under CNES contract. [ts objectives are : - primarily : an operational world-scale survey of the evolution of vegetation (forecasting of agricultural yields and environmental studies). - secondarily : the observation of oceanic areas. Field of view is ± 50,5°C (2000 km on ground), with observation frequency of less than 2 days at equator. The system, equipped with its own telemetry channels and on-board computers, will send coded data according 2 types of observation : - world wide observation : recording, then time-tagged transmission, with a nadir resolution of 1,165km x 1,165 km or (in an exclusive sense)4,66 km x 4,66km (agglomeration of 16 pixels). - regional observation real-time transmission, with a nadir resolution of 1,165km.

Optical inter-satellite links are foreseen in ESA's satellite communication projects for the linking of two geostationary telecommunication satellites and in the context of the European Data Relay Satellite project (DRS). In preparation of these missions, a Payload and Spacecraft Demonstration and Experimentation (PSDE) programme has been set up for the in-flight demonstration of optical space links in the early 1990s. This paper reports on the progress of system studies and related technology developments.

Present status of optical intersatellite link (ISL) research and development activities and related optical technologies in Japan are introduced, placing emphasis on semiconductor laser diodes, photo detectors, CCDs and modulation/demodulation techniques. Subjects for further research on optical devices and communication schemes are summarized.

Optical technologies are going to challenge state of the art RF communication systems in future IOL, ISL and deep space scenarios. In addition, electrooptical systems are being considered by ESA and various national space agencies for space operational solid earth and atmospheric LIDAR and navigtion applications. This paper summarizes the present status of the CO₂ laser technology development and emphasizes the potential of emerging CO₂ hardware components and subsystems for future optical space mission scenarios.

The basic requirements for an optical intersatellite/interorbit link are viewed. The most important of these - long life time, sufficient reliability, high redundancy, high power output - lead to a systems approach based on a diode-laser-pumped Nd:YAG-laser system. Based on this technology several systems are discussed and compared to each other with respect to their performance, complexity and receiver sensitivity. It is shown that a system using diode-laser-pumped Nd:YAG-lasers and homodyne detection meets the requirements for future optical communication links.

In view of the European Data Relay Satellite, a system based upon GaA1As laser diodes transmitters and direct detection receivers has been proposed. This paper addresses the problem of link-budget optimization and focuses on its interrelation with acquisition, pointing and tracking performances. Possible means for supporting variable communications requirements are proposed ; the main characteristics of possible USER-terminal "standards" are briefly outlined.

The National Commission on Space was chartered by the President and Congress of the United States to formulate the future direction of the U.S. National Aeronautics & Space Agency civilian space program. One of the recommendations is the pursuit of an aggressive space science program. Its focus should be on three major objectives. The first is to understand the structure and evolution of the universe, our Galaxy, our Solar System and, finally, the Planet Earth. The second is to apply this understanding to forecast future phenomena of critical significance to humanity. Finally, the last objective is to use the environment of spaceflight and the tools of space technology to study the basic properties of matter and life.

The data transmission and position determination of deep space probes is today performed with microwave systems. Large antennas have to be used at ground (up to 300 m in diameter) and on board (several meters in diameter). Low data rates of the order of 100 Kbps must be transmitted. The position of the deep space probe can be determined from Doppler measurements of the microwave carrier from observations made over some days. The application of advanced optical data links allows both a reduction of antenna diameters and position determination error by orders of magnitude. For a typical mission to planet Jupiter three different optical technologies are considered, using CO₂, Nd:YAG and semiconductor diode lasers. The first two systems allow the realization of coherent optical transponders which are required for a two way Doppler measurement with the optical carrier. For the semiconductor laser system direct detection with pulse position modulation is assumed. Consequently position determination of the spacecraft can not be made as precise as with microwave or CO₂ and Nd:YAG systems. The assumed laser diode pumped Nd:YAG laser with a modulated output power of 10 W and a tunable diode laser pumped-Nd:YAG laser local oscillator are not available at the present time. But the clear advantage of this technology for deep space missions must be taken into account for further technological developments.

ISDN standards are examined in order to estimate performance criteria that will be required for optical ISLs. To make the estimates, a percentage of the degradation allowed for the end-to-end link is assigned to the ISL and a simplified model of antenna pointing errors are used. Two criteria are found to be sufficient to meet ISDN standards. The first criterion is that the probability of a burst error with a BER greater than 3 x 10-2 must be less than 1.6 x 10-7. The second criterion is that the sum of (a) the average BER (exclusive of burst errors) and (b) 8 x 1O the probability of burst errors (having BERs greater than 8 x 10-3) plus the average BER (exclusive of burst errors) must be less than 6 x 10-8. The impact of these criteria, which depend upon the bandwidth of the tracking subsystem, are examined for several links of differing noise equivalent angles and laser powers. It is concluded that optical ISLs should be able to meet the ISDN standards if noise from the tracking detector is the dominant source of pointing errors.

Digital satellite communication links are usually characterized by transmission capacity, link distance, bit error rate, availability and lifetime. For optical data links however an additional parameter, the burst error rate has to be specified. The physical reason for occurence of burst errors lies in the required precise mutual tracking of both satellite communication terminals. The influence of the statistical motion of both satellites around their nominal attitude on optical data link performance has been studied by computer simulations. Improvements achievable with forward error correcting coding are analysed. These simulation results are based on a Gaussian distribution of indenpendently vibrating satellites. Realistic values for simulation are obtained by multiplication with the Fourier transform of complex transfer function of spacecraft motion.

Laser communications between satellites imply stringent demands concerning the accuracy of the Pointing, Acquisition and Tracking (PAT) Subsystem which is part of the transceiver package. In the scope of ESTEC and DFVLR contracts a breadboard model of a PAT subsystem is being developed. This subsystem is designed for a CO₂-laser transceiver package. The PAT subsystem is composed of four opto-mechanical subassemblies namely the Coarse Pointing Assembly (CPA), the Fine Pointing Assembly (FPA), the Optical Nutator Assembly (ONA) and the Point-Ahead Assembly (PAA). The actual pointing mechanism is composed of the CPA and the FPA. The CPA provides the PAT with a hemispherical pointing range but allows only low dynamics and a limited pointing accuracy. Hence, the FPA's part is to cope with high-speed, small-angle precise beam steering. Furthermore, the FPA is used to generate the search pattern in the acquisition mode. The PAA deviates the received and the transmitted beam to compensate the effects caused by the propagation time of light between the satellites. By means of the conical scan tracking technique the ONA allows the generation of the tracking signal for the FPA from the same detector which is used for data reception. This paper describes the control loops and steering algorithms which are necessary for proper interactions of the subassemblies. In particular the acquisition strategy and the transition from the acquisition mode to the tracking mode is described. The subassemblies and the control electronics are modeled. Problems concerning the CPA singularity are discussed. The performances of the control loops and the interactions of the subassemblies are demonstrated by means of computer simulations verified by some hardware tests.

Bimorph piezoelectric elements show relative large axial displacements at moderate voltages. Their response to voltage variations is very fast. The re-produceability of the displacement is practically limited only by the mechanical and electrical supplementary equipment. In combination with a deflection mirror linear scans or two-dimensional scan pattern can be generated. Fast scanning with good linearity and repeatability is possible, either in a resonant mode or in a random acces mode. However, the hysteresis of the piezoelectric material and the large capacitance of the elements impose some constraints on the applicability of the piezoelectric scanners. In the first part of the paper the properties of piezoelectric elements are discussed in view of scanner application; in the second part an experimental single mirror two-axis piezoelectric scanner is described. Some suggestions for future applications of piezoelectric scanners are made.

Most of intersatellite links use APD 4 quadrant tracking systems. This presentation shows that CCD Arrays can be used not only for acquisition but also for tracking with improved pointing accuracy. High frequency image repetition rate up to 8,000 Hz is possible with commercialy avalaible components. Experimental verifications performed in CNES Laboratories are described.

A cooler/detector/preamplifier unit to be used as the front end in coherent optical receivers for X = 10pm was designed, fabricated, and tested. Both the HgCdTe-detector and the preamplifier were cooled to 80 K with the aid of a Stirling cooler. The three-stage high-impedance preamplifier realized employs field effect transistors and can hence be operated at low temperatures, too. Receiver tests were performed at a data rate of 140 Mbit/s using a quasi-homodyne receiver setup, with the bit-error-rate as the criterion of performance. Receiver operation very close to the quantum limit was demonstrated.

An in-flight check-out and monitoring approach for an optical communication transceiver terminal on-board a communication satellite will be described. Primarily an inter-pretation of available payload input parameter characteristics will be used, which has no detrimental effect on payload's basic function and which requires only a minimum of additional diagnostic hardware. A method to check out the optical payload pointing, acquisition and tracking function without a counter terminal will be described and means to monitor laser output power at telescope level will be outlined.

A laboratory model of a bidirectional semiconductor laser data link package with acquisition and tracking capability was realized and tested. The system consists of two independent transceivers spaced at a distance of typically 20m. The transceivers are built around a GaAlAs-laser (X=0.85μm) and a Ge-photodiode in one case and an InGaAsP-laser (X=1.3μm) and Si-detectors in the second case. The 0.85pm beam carries a 10Mbit/s data stream, while the 1.3μm beam transmits a low-data-rate signal at 160kbit/s. One transceiver is mounted on a test jig which permits transverse movement over an area of 1m x lm. At a transmitted optical power level of 0.5mW reliable data transmission (BER<10-9), pointing, acquisition (^Tacquisition<10s), and tracking (NEAz2Oprad) were demonstrated.

Optical space communication systems now under development need thorough testing and performance verification before transportation into space. However, due to the shortcomings encountered in laboratory and ground environment especially by atmospheric disturbance and short distances, tests cannot be performed satisfactorily and performance prediction has to rely strongly on analytic methods. The suggested experiment on stratospheric balloons at altitudes above 30 km can improve significantly the test conditions at low costs in comparison to space experiments.

Thermal and radiometric calibration test procedures for the ISAMS instrument are described. Computer model predictions for the thermal behaviour of the instrument are presented and discussed in terms of their relevance to instrument performance verification by means of a thermal test programme. Results of theoretical calculations for the radiometric calibration targets are given.

A newly designed laboratory facility at Oxford which is used to test and calibrate space instrui ents in a thermal vacuum chamber is described. The design of three space environment panels, used to mimic the predicted thermal loading of the ISAIAS instrument on the UARS satellite, is outlined.

We propose a multiplexing process based on polarized light and which gains distinction from other systems based on polarization by the number of channels that it allows to transmit: three radio-frequence (RF) distinct signals instead of two can indeed circulate inside a single optical fiber and be then simultaneously detected. In fact, the RF signals to transmit (made up in our experiment of video signals) modulate monochromatic plane lightwaves linearly polarized along directions of vibration oriented at 60° from each other. Light is injected in a single-mode fiber a few meters long. At the output, after division in amplitude and crossing through three suitably oriented analyzers, we collect three light beams whose values are known linear combinations of original signals. So it is possible to retrieve the original signals by electronic inversion of a matrix. The use of a single-mode fiber is necessary in order to preserve as much as possible the state of polarization. We present the results obtained by means of curves and TV pictures and we emphasize the advantage of such a process in high data rate transmission on short and medium distance.

This paper describes a method for accurately and simply calculating the effective emissivity of a grooved surface, and analyses the uncertainties. Using this method, the directional and hemispheric emissivities of a grooved surface are calculated and the results dis-cussed. The method further permits an accurate determination of the normal and hemispheric emissivity of a cylindrically baffled grooved plate source.

The paper covers two sensors for the French SPOT satellite : . a 4096-element device made in three-level polysilicon gate MOS/CCD technology and active in the visible and near infrared spectral bands; a 3000-element detector for the SWIR (1.5 µm - 1.7 μm) spectral band, implementing InGaAs photodiodes of 30 pi x 30 1,1m elementary dimensions and two CCD multiplexers.