Multilayers clouds layer's horizons have been detected in strong snowing condition by using the micro-Joule eye-safe lidar. Lidar is based on the 1 μJ (30 ns length) pulsed diode laser, which operates with high repetition rate (up to 10 kHz) and silica (Si) photon counting receiver (Single Photon Avalanche Diode, SPAD) from Czech Technical University. Note that the unique low avalanche voltage of Czech SPAD (~ 26-28 Volts), low power consumption (~ 0.2 Watts), the wide (-100 to 20 °C) temperature operation and low weight (~ 0.94 kg) were the main arguments to involve this lidar version into the NASA Mars Polar Lander mission a decade ago in 1999. The Geiger (photon counting) mode of SPAD operation and laser high repetition rate allow us to apply the specifically statistical approach to the development of the remote sensing return, which is scattered by aerosol and other inhomogeneous along the sounding trace. To get of reliable signal-to-noise ratio (SNR) we have to use a few hundred or thousand laser pulses because the probability of the photon scattered by sounding object is smaller than unit. As a role a Poison statistics is used to development of the remote sensing return.

The purposes of the Laser Time Transfer (LTT) experiment are to synchronize the atomic clocks in space to ones on the ground, and to verify the relativity theory. The LTT payload in space includes a dual-SPAD detector, a timer based on TDC device, control unit and a LRA. The expected uncertainty of measurement of clock differences for single shot is about 200ps, and the uncertainty of measurement for the relative frequency differences for two rubidium clocks is about 5×10/ 1000 seconds. The LTT flight module is ready and is waiting for the flight mission in 2007-2008. Introduction Based on the successful time transfer by laser pulses between ground stations in 2003, the Laser Time Transfer (LTT) project between satellite and ground stations was initiated in 2004. The goals of the LTT are as follows: 1) Evaluation of performance of space clocks which are rubidium’s now, and will be hydrogen clocks in the future. 2) Verification of the relativity Shanghai Astronomical Observatory, in cooperation with the China Academy of Space Technology in Beijing, has been in charge of the LTT project. The Philosophy of the project is to make a payload as simple as possible on a satellite in a short time to verify the capability of the time transfer by laser pulses between space and ground clocks. So, a simple 40um SPAD detector with 100ps timing resolution and the TDC devices with lower resolution(125ps) have been chosen for the space module. The LTT project has kept going smoothly since 2004. The flight module has been built and has passed the space environmental testings.

Using precise Lageos-1/2 orbit generated by the DOGS (DGFI Orbit and Geodetic Parameter estimation Software) Package ( http://ilrsac.dgfi.badw.de/dogs ), multiwavelength tracking data from Zimmerwald and Concepcion were analysed. We solved for station coordinates and color dependent biases. Some statistics and the history of bias differences for various tropspheric refraction models are shown. Additionally the available full-rate tracking data were analysed to see if there are differences to the biases obtained from the onsite normal points. The results show that the switch from internal to external calibration at Zimmerwald give a significant improvment of the relative biases, mainly from the infrared part. Finally we tried to rate the refraction models from the resulting bias differences.

We are presenting the results of the research and development of an avalanche photodiode structure, on the basis of SiGe epitaxial layer on Si wafer. The ultimate goal is to develop a solid state photon counting detector with picosecond timing resolution and stability and a spectral sensitivity beyond 1100 nanometers. The technology development steps on the Si0.6Ge0.4 epitaxial layer are presented together with the first results of the preparation of the shallow junction and its parameters. The ability of the avalanche structure to operate in a Geiger mode has been demonstrated for the first time. The serial resistance of the structure above its breakdown voltage has been measured. The diffusion and annealing model has been tuned for GeSi epitaxial layer and implantation. The resulting concentration profiles have been verified by two independent diagnostics methods. ne rapidity of avalanche grow was compared with Si photon counting diode.

The European space agency has nominated the laser altimeter as one of the principal devices for planetary research for the next decade. The device should be capable of ranging over distances of 400 - 1000 km and of acquiring information about the probe altitude above the planet surface and about the surface terrain profile with a precision of the order of 1 m. Recently, the technology demonstrator of the altimeter has been under development at the German Air and Space Agency, Institute of Planetary Research, Germany. The altimeter technology demonstrator is based on a diode pumped frequency doubled Nd: YAG laser delivering 50 mJ at 532 nm in 3 ns long pulses with the repetition rate of 20 kHz. The solid state echo signal detector in photon counting mode will be used. The optical part of the altimeter is scaled down to simulate the real background count rate scenario and to reduce the energy budget link by a factor of 104 at the same time. The demonstrator should be capable of ranging objects at distances of 0 - 5 km in both night and day time. We present the concept, design and construction of the timing system and detector part of the laser altimeter technology demonstrator, which has been developed at the Czech Technical University in Prague, optimized for the photon counting altimeter concept. The timing system has interval resolution 0.25 ns, stability and linearity similar to 0.1 ns, epoch resolution 100 mu s and accuracy 1 mu s, and a programmable range gate.

Single photon avalanche diodes (SPADs) based on various semiconductors have been developed at the Czech Technical University in Prague during the last 20 years. Much attention has been also paid to development of high-speed active quenching circuits for these detectors. Recently, we have performed a series of experiments to characterize our silicon-based photon counters and their capability of operation in a gated mode with the gate duration of single nanoseconds and the detector sensitivity rise time of hundreds of picoseconds. This performance has been achieved by optimizing the active quenching circuit and its components. The fast gating is needed in cases, when the photons of interest are generated short time after a strong optical signal, which cannot be suppressed in optical domain. The time dependence of detection sensitivity, detection delay and timing resolution within the nanosecond gates has been measured.

The paper reports the results of research and development of a single photon avalanche detector (SPAD) for use in the harsh and hostile conditions of outer space. The photon counting detector was developed for space projects related to the synchronization of timescales via a space clock using optical pulses. The detector is based on a SPA D manufactured on silicon using the K 14 process, and operated in an active quenching mode. Its operation over an extreme temperature range and under high optical overload has been tested together with its sensitivity to radiation in space. The technology demonstrator of the detectors for the China Laser Time Transfer mission was developed and tested. The mission launch is expected in the year 2008.

We are presenting the design, technology development and tuning of the Single Photon Avalanche Diode fabricated on the germanium - silicon epitaxial layer. The ultimate goal is to develop a solid state photon detector with picosecond timing resolution and stability and an increased spectral sensitivity beyond 1100 nanometres in comparison to detectors based on silicon. The technology development steps on the Ge-Si epitaxial layer are presented together with the first results of the preparation of the shallow junction and its parameters. The diffusion and annealing models have been tuned for GeSi epitaxial layer and implantation. The resulting concentration profiles have been verified by two independent diagnostics methods. The first avalanche diode structures on the basis of the Ge0.4Si0.6, epitaxial layer on Silicon have been prepared and tested. The ability of the avalanche structure to operate in a Geiger mode has been demonstrated for the first time, the dark count rate has been measured. The serial resistance of the structure above its breakdown voltage has been measured. The detection sensitivity in the wavelength range of 500 to 1600 nanometres has been measured.

The paper reports on detailed tests of active area uniformity of three different single photon avalanche detectors (SPADs). Relative sensitivity, timing jitter, and relative detection delay have been measured for a series of points across the detection area; the resulting spatial profiles have been plotted and analysed. Unique features have been found in the case of silicon-based K14 SPADs: their active area is extremely uniform, especially with respect to the detection delay, in contrast to the remaining two SPADs, which exhibit significant fluctuations of the delay. The perfect uniformity of the K14 SPADs enables the detector to maintain its high temporal resolution of 40 ps FWHM even for large detection areas of 200 mu m diameter.

We are presenting the design, construction and performance of the compact control circuit of the InGaAs photon counter. The main design goals were to construct a detector control circuit, which enables the InGaAs photon counters to operate in gated mode, the detection window width adjustable 3-10 ns with repetition rate reaching 2 MHz. The short detecting window requires the nanosecond rise/fall edges of gating pulse. The gating pulse minimum amplitude of 5 Volts is needed. The control circuit consists of the gate signal receiver, level converter, gate driver, avalanche breakdown sensor and a detector bias control circuit with fast current limiting option. The entire circuit has been tested in connection with different InGaAs detection chips operated at room temperature and thermoelectrically cooled with gate width in the range of 3 to 10 nanoseconds and gate repetition rate up to 5 MHz. The entire circuit is quite compact 60 x 60 mm in size, it is powered with external stabilized supply +5 V and -6 V. Although the main foreseen application was quantum cryptography, the control circuit can be used in connection with various avalanche photodiodes and in different applications.

The goal of the presented experiments is the development of new optical tracking techniques for space objects, namely space debris, based on simultaneous CCD and laser measurements: the CCD tracking of a laser illuminated object, the simultaneous CCD tracking and laser ranging and the laser time-tagging of the CCD tracking. The first two experiments can be performed on cooperative corner retro-reflectors equipped satellites while the third one is applicable to any space object and to space debris in particular. The high accuracy and density of laser ranging data and additional Time-tags in the CCD image, atmospherically back scattered photons, can contribute to the solution stability of computed orbits from data based even on a single tracking location within a single pass.

Avalanche photodiodes specifically designed for single photon counting semiconductor avalanche structures have been developed on the basis of various materials: Si, Ge, GaP, GaAs and InGaAs at the Czech Technical University in Prague during the last 20 years. They have been tailored for numerous applications. Recently, there is a strong demand for the photon counting detector in a form of an array; even small arrays 10x1 or 3x3 are of great importance for users. Although the photon counting array can be manufactured, there exists a serious limitation for its performance: the optical cross-talk between individual detecting cells. This cross-talk is caused by the optical emission of the avalanche photon counting structure which accompanies the avalanche multiplication process. We have studied in detail the optical emission of the avalanche photon counting structure in the silicon shallow junction type photodiode. The timing properties, radiation pattern and spectral distribution of the emitted light have been measured for various detection structures and their different operating conditions. The ultimate limit for the cross-talk has been determined and the methods for its limitation have been proposed.

Solid-state single photon detectors based on avalanche photodiode are getting more attention in various areas of applied physics: optical sensors, quantum key distribution, optical ranging and Lidar, time-resolved spectroscopy, X-ray laser diagnostics, and turbid media imaging. Avalanche photodiodes specifically designed for single photon counting semiconductor avalanche structures have been developed on the basis of various materials: Si, Ge, GaP, GaAsP, and InGaP/InGaAs at the Czech Technical University in Prague during the last 20 years. They have been tailored for numerous applications. Trends in demand are focused on detection array construction recently. Even extremely small arrays containing a few cells are of great importance for users. Electrical crosstalk between individual gating and quenching circuits and optical crosstalk between individual detecting cells are serious limitation for array design and performance. Optical crosstalk is caused by the parasitic light emission of the avalanche which accompanies the photon detection process. We have studied in detail the optical emission of the avalanche photon counting structure in the silicon- and gallium-based photodiodes. The timing properties and spectral distribution of the emitted light have been measured for different operating conditions to quantify optical crosstalk. We conclude that optical crosstalk is an inherent property of avalanche photodiode operated in Geiger mode. The only way to minimize optical crosstalk in avalanche photodiode array is to build active quenching circuit with minimum response time.

We are presenting the results of research and development of the Single Photon Avalanche Detector (SPAD) for application in a Laser Time Transfer (LTT) space mission. For the joint project with the Shanghai Observatory, Academy of Sciences of China, we have developed the detector package dedicated for the project of synchronizing the hydrogen maser-based time scales by laser pulses. The technology demonstrator of a dual detector has been built and tested in our labs. The main parameters are: detection efficiency 10% at 532 nm, timing resolution 80 psec, dark count rate 8 kHz, non gated operation. The detector's active area is 25 um in diameter. The total mass, including bias stabilizing circuit, is 2 grams, and the total power consumption is below 0.5 Watt per detecting channel. The detector can be operated in a wide range of temperatures ranging from -30o C to +60o C without any additional temperature control. Figure 1: The technology demonstrator of the dual photon counting detectors. The detection chips (protective caps installed for handling) are on the left. The ruggedness of the detector is superb. Optical power of 2 mW has been focused onto a sensitive area while the detector has been biased for 8 hours. No detectable degradation has been experienced. The overload tolerance negates the need for any mechanical Sun protection shutter in space. The recovery time from optical overload to full functionality is less than 0.1 second. The detector package has been successfully integrated into the LTT timing electronics and the pre-flight test was performed in China during the period July-September 2006.

The European Space Agency has nominated the laser altimeter as one of the principal devices for planetary research for the next decade. The first mission in view is Mercury with scheduled launch in 2010. The device should be capable to range over the distances 400 to 1000 kin and to acquire the information about the probe altitude above the planet surface and about the surface terrain profile with the precision of the order of one meter. The requirements on the device are rather strict: total mass below 5 kilograms, power consumption below 10 Watts. Recently, the Technology Demonstrator of the altimeter is under development at German Air and Space Agency, Institute of Planetary Research, Germany. The altimeter Technology Demonstrator is based on the diode pumped frequency doubled Nd:YAG laser delivering 50 mJ at 532 run in 3 nanosecond long pulses with the repetition rate of 20 kHz. The solid state echo signal detector in photon counting mode will be used. The optical part of the altimeter is scaled down to simulate the real background count rate scenario and to reduce the energy budget link by a factor of 10(4) at the same time. The demonstrator should be capable to range objects at distances 0 - 5 kilometers in both night and day time. We are presenting the concept, design and construction of the timing system part of the laser altimeter technology demonstrator, which has been developed at the Czech Technical University in Prague optimized for photon counting altimeter concept. The timing system has interval resolution 0.25 ns, stability and linearity similar to 0.1 ns, epoch resolution 100 ns and accuracy 1 mu s, and programmable range gate.

The Laser Induced Fluorescence is a well-known and established analytical technique. We are reporting on the research and development of the remote sensing technique for water pollution of the organic pollutants dissolved in the water or flowing on the water level. The recent development in diode pumped compact micro lasers, solid state photon counters and fast timing electronics opens quite new application possibilities. We are relying on the diode pumped Nd:YAG microlaser, passively Q-switched and frequency doubled. It provides pulse energy exceeding 100 nJ in 600 ps long pulses at 532 nm with the repetition rate of 10 kHz within a compact, small and low power package. The fluorescence signal is detected by the customized silicon photon counting detector. The compact time-to-digital converter with 20 ps timing resolution and a personal computer interface has been constructed for the device. The small receiving optics apertures together with advanced time gating of the detected signal permits to operate in an outdoor environment in daylight background conditions with acceptable signal to noise ratio. The first measurement results. the capabilities of the technique in the environmental monitoring along with the device construction will be presented.

We are reporting our results in research and development in the field of avalanche semiconductor single photon detectors and their application in high precision laser ranging during the last 20 years. Our objectives where: avalanche detector structure, sensitive area diameters exceeding 50 microns, active quenching and gating electronic circuit, high timing resolution and rugged design. Avalanche photodiodes specifically designed for photon counting devices have been developed on the basis of various semiconductor materials: Si, Ge, SiGe, GaP, GaAs and InGaAs. All the semiconductor detectors operate at a room temperature or at thermoelectrically achievable temperatures except of the germanium based detector, which requires liquid nitrogen cooling. Electronic circuits for these detectors biasing, quenching and control have been developed and optimised for different applications. Circuits permitting operation of solid state photon counters in both single and multiple photon signal regimes have been developed and applied. Additionally, these circuits provide the estimate of the photon number involved in the detection process. The timing resolution of the order of units to several tens of picoseconds enables millimeter precision laser ranging. The different photon counting detectors for applications in ground-ground, ground-air, air-ground and ground to space high precision laser ranging have been developed and operated in the field on 11 different wavelengths in the range of 355-1548 nanometres.

Avalanche photodiodes specifically designed for single photon counting devices have been developed on the basis of various semiconductor materials: Si, Ge, GaP, GaAsP, and InGaAs at the Czech Technical University within the last 20 years. All the semiconductor detectors operate at a room temperature or at thermoelectrically achievable temperatures except of the germanium-based detector, which requires liquid nitrogen cooling. Electronic circuits for these detectors biasing, quenching and control have been developed and optimized for different applications. Timing resolution of solid-state photon counters as high as 50ps full width at a half maximum has been achieved when detecting single photon signals. Circuits permitting operation of solid-state photon counters in both single and multiple photon signal regimes have been developed and applied. The compact and rugged design, radiation resistance, and low operating voltage are attractive features of solid state photon counters in various applications including the space projects. The sensitivity of solid-state photon counters spans from X-ray up to 1800nm in the near infrared region. The avalanche structures based on the GaP material exhibit several special features for X-ray operation: the timing resolution as high 100ps may be achieved when detecting individual quanta, the wavelength range spans from 0.1nm up to visible light. The GaP exhibits from all the existing solid-state photon counters the highest detection efficiency in X-ray, it reaches 14% at 0.1nm band.

The paper introduces the performance of the experimental laser ranging system for space debris at the Shanghai Observatory. The output of laser is 2J in 532nm, 10ns, 20Hz, 40W. A new transmitting telescope with the aperture of 210mm is used, and the other parts of the ranging system are the same with the routine SLR system in Shanghai. The ranging system is under testing now. Introduction China has launched many spacecrafts into space and had produced many space debris during 30 years. China is one of the members of IADC (Inter-Agency Space Debris Coordination Committee). It is necessary for China to pay great attention to reduce damages from space debris in cooperation with international community. The project of laser ranging to space debris at Shanghai Astronomical Observatory is supported by the Chinese Space Agency. An experimental laser ranging system for space debris at Shanghai is set up in 2006. The goals of the project are as follows: 1) Development of the technology for space debris laser tracking. 2) Experimental observations and orbit determinations for space debris, not routine observations. 2. Performance of the system The major parts of the space debris ranging system are the same with the SLR system at Shanghai. A China-made 40W Q-switched Nd:YAG laser has been installed and is located at the neighbor room to the mode-locked laser for SLR. There are ten Nd:YAG rods in the laser with the output of 2J in 532nm, 10ns width, 20Hz repetition, 0.6mrad divergence. A new transmitting telescope with 210 mm aperture was installed and replaced the old one with 150mm aperture for better collimating beam. The testing of laser ranging to the satellites with retro-reflectors has been done. The next step will try to ranging to uncooperative space targets soon. Some photos for the system are shown as follows. Fig.1. The Optical Observation Site at Shanghai Observatory, CHINA Fig.2. SLR House in Shanghai Fig.3. SLR Telescope(Aperture 600mm) Fig.4. Electronics Room Fig.5. High Power Laser & Power Supply, Chiller Fig.6. Output of High Power Laser Fig.7. Inside of the 40W Pulsed Nd:YAG Laser Fig.8. Coupling Optics Fig.9. Laser Firing (2J, 20Hz, 40W in 532nm) Fig.10. Laser Firing