LIST OF ABSTRACTS

Session 8: Lasers, Detectors, and Timers

Advances of High-precision Riga Event Timers

Yu. Artyukh, V. Bespalko, E. Boole, V. Vedin
Institute of Electronics and Computer Science, Riga, Latvia
E-mail : artyukh@edi.lv

Currently there are two main directions to advancement of high-precision Riga event timers. Firstly, we are updating the well-known model A032-ET of commercially available event timer, mainly in terms of its resolution. Retaining the basic operating characteristics of A032-ET (linearity, dead time, etc), we increase its RMS resolution from previous 7-8 ps to 3-4 ps. In process of the timer's updating the PCB design is fully revised, obsolete electronic components are replaced by latter-day ones. In addition to the basic EPP interface for data exchange with PC, optionally we provide for other kinds of interfaces (USB, DIO, etc) on special request. As a whole this updated model of event timer should replace the model A032-ET in the nearest future.
Secondly, we are developing an event timer module (ETM) fitted to including into various customized timing systems. Functionally ETM is similar to the above design but in this case an emphasis is made on achievement of a maximally compact technical solution due to the higher hardware integration level. The pilot model of ETM provides: single measurement input (NIM), <4 ps RMS resolution, 40 ns dead time, built-in internal clock synthesis from 10 MHz time-base, replaceable (as an option) interface. Dimension of the module card - 130x120 mm, power consumption - <6W. In process of further development we hope for advancing of the noted performance characteristics

Advances of multi kHz repetition rate picosecond laser system for satellite laser ranging

Huber Heinz, Schmidt Michael, Zoppel Sandra
High Q Laser Production GmbH, Austria
E-mail: heinz.huber@highqlaser.at

Saturable absorber mode locked and diode pumped picosecond laser systems at a repetition rate of 2 kHz have been successfully introduced for SLR (by the Graz station) nn previous years. These system were based on the laser material Nd:Vanadate. A better candidate to reach higher pulse energies is the laser material due to its higher laser state life time.
Here we present a new Nd:YLF laser system delivering 1.2mJ at 1 kHz and 0.6mJ at 2 kHz. The system exhibits a simpler set-up and can run up to higher repetition rates.

Josef Koelbl, Michael Froeschl, Adam Seedsman, Yue Gao, Murray Dawson
EOS Optronics GmbH, Germany
E-mail: sandra.weidmann@eos-optronics.com

Poster: The presented research was concentrating on the development of ultrafast Pockels cell driver for ultrafast, high repetition rate and high energy Laser system. Pockels cells can be used for regenerative amplifier, pulse slicer (pulse picker), and other fast optical switching system in SLR Laser and other types of Laser systems.
The devised driver electronics for the actual Pockels cell is specifically characterized that two Pockels cells can be connected and simultaneously driven with a fast slope of 9.5 kV in less than 11 ns, even at high Laser repetition rates of up to 2 kHz. By using a push-pull switching arrangement, a variable and low-jitter impulse width from 80 ns to 2.3 μs is achieved. Due to the drive capability of the circuit, more than one Pockels cell can be cascaded whilst maintaining very fast switching performance.

Compact Event Timing and Laser Fire Control Device for One Way Laser Ranging

Jan Kodet, Ivan Prochazka
Czech Technical University in Prague, Czech Republic
E-mail : kodet@fjfi.cvut.czbr

We are presenting the design, construction and performance of the compact control circuit, which can be used as a event timing unit and time laser fire control unit in one way ranging experiments. The main design goals were to construct compact device, which can measure time epochs with resolution of hundreds picoseconds and which can control the time of laser fire with resolution of 100 nanoseconds.  The unit is controlled by 10 MHz and 1 pps signals from local time base.
The electronic board is designed using SMD technology, the precise voltage stabiliser is included. The external power of 4.5 to 9 Volts 0.5 A DC is required. The input signals receivers accept TTL (1 pps) and NIM (Event) signal levels via SMA connectors. The epochs are determined using coarse counter and time interpolator. The coarse counter determines both the epoch of laser fire and received pulses with resolution of 100 nanoseconds, it is based on programmable gate array. The time interpolator by Acam provides the epoch of received pulses resolution of hundreds of picoseconds. The unit is controlled by microcontroller made by Microchip, it communicates through standard serial line - RS232 using ASCII characters. The user friendly controlling application for the device was developed. Maximum measurement rate exceeds 100 Hz.
The device was tested in our lab and complete set of measurement were produced. The timing unit was compared to Pico Event Timer (P-PET2k) and the epoch timing resolution of the device is 130 picoseconds rms, the warm up characteristics does not exceed ~160 ps/K, the warm up time is one hour. The long term stability is as low as 10 ps/hour and the non linearity is below +/- 125 ps.
The device may be simply integrated to any SLR (or similar) system, it is compact, easy to control and friendly to use hence it satisfies the requirements variety range of experiments. The device was mainly designed for one way laser ranging to the Lunar Reconnaissance Orbiter and similar experiments.

Photon counting detectors for future laser time transfer missions

Ivan Prochazka, Josef Blazej
Czech Technical University in Prague, Czech Republic
E-mail : prochazk@fjfi.cvut.cz

We are reporting on research, development and indoor tests of the photon counting detectors that are being developed in our lab for future space missions related to precise time transfer by laser pulses. The detectors are optimized for an on-board detection and precision time tagging of an incoming laser pulse. The key parameters of the detectors are: detection delay stability, broad operation temperature range, capability to operate under high background photon flux, radiation tolerance, mass and power consumption and overall ruggedness. The timing resolution, detection quantum efficiency and the dark count rate are of lower importance.  The most challenging requirements are the detection delay stability of the order of units to tens of picoseconds within the temperature range of -30 to +50 C and the detection delay stability under the conditions of extremely high background photon flux well exceeding 108 photons per second hitting the detector active area.
The first detector version is based on the 25 micrometer diameter active area K14 SPAD chip. The new active quenching and gating electronics has been developed, it enables the operation in both gated and non gated modes. In a gated mode the detector is capable to operate - detect individual photons - under the condition of background photon flux exceeding 10E9 (!) photons per second. The detection delay temperature stability of ~10 ps is maintained by custom designed SPAD bias circuit and selection of a low temperature drift comparator.  The detector is compact, its mass is below 100 grams and power is below 1 Watt.
The second version of the detector is based on 200 micrometers diameter K14 SPAD chip operated in gated mode. The timing stability ~ 1 ps is maintained by means of active temperature stabilization of both the detection chip and the detector electronics. Additionally, the detected photon number may be estimated. Optional time walk compensation may be applied on a data post processing level within the range of 1 - 10000 photons per echo. This detector version mass estimate is below 300 grams and power consumption is 3 - 5 Watts.

Progress in sub-picosecond timing system development

Ivan Prochazka, Petr Panek
Czech Technical University in Prague, Czech Republic
E-mail : prochazk@fjfi.cvut.cz

We are reporting on research, development and indoor tests of the novel principle event timing system based on Surface Acoustic Wave (SAW) filter excitation as a time interpolator. Its operating principle is based on the fact that a transversal SAW filter excited by a short pulse can generate a finite signal with highly suppressed spectra outside a narrow frequency band. If the responses to two excitations are sampled at clock ticks, they can be precisely reconstructed from a finite number of samples and then compared so as to determine the time interval between the two excitations. We have designed and constructed a two-channel device which allows independent timing of two events. The device has been constructed using commercially available components, it is built in a standard 19" rack of 2 unit height. The inputs are two NIM signals for epoch channels A and B and the 100MHz or 200MHz clock signal. The device is interfaced using USB type 1 interface to a host personal computer for data acquisition and processing.
We have assessed the single-shot event time measurement precision of 0.9 ps r.m.s. per channel. The device exhibits extremely high timing linearity; the non-linearity is +/- 0.2 ps over an entire interpolator range. The temperature drift of the measured time interval is lower than 0.3 ps / K, the long term stability is better than +/- 0.1 ps per hour.  These are to our knowledge the best values ever reported. These values were measured on the first prototype constructed without any additional temperature compensation or stabilization. The measurement dead time is 10 microseconds, the maximum continuous measurement rate is 2.5 kHz. The limiting factor is the data transfer and computing power of the personal computer. Significantly higher rates may be achieved using custom tailored embedded processors.

Potentialities of common-used TDC chips for high-speed event timer design

E. Boole, V. Vedin
Institute of Electronics and Computer Sciences, Riga, Latvia
E-mail : vedinv@edi.lv

Basically commercially available TDC chips are not meant for continuous event timing. Nevertheless it is of interest to use their most attractive features (high speed, low power consumption, extended functionality, etc) for designing of true event timers. Specifically, we have used a high-performance TDC-GPX from Acam-messelectronic Gmbh as a core for such design. Some problems concerning TDC tailoring to continuous operation have been solved, careful evaluation of the main operating characteristics (resolution vs. event rate, channel cross talk, linearity) was done.
As a whole, this work has resulted in a pilot model of high-speed event timer with unlimited range of time measurement. It is implemented as a compact stand-alone device connected to PC via its USB port and provides 6 independent measurement channels (including 4 channels with programmable thresholds for input signals), 80 ps RMS resolution and input event burst rate up to 150 MHz for each channel. The mean rate of continuous measurement (aggregate for all channels) is up to a few MHz. Timer's pilot software is written in LabWindows CVI and may be incorporated into various application-specific timing systems.
Generally it can be concluded that some part of currently available commercial TDC chips are well applicable for event timer designs, above all intended for applications where compact implementation and high rate of multi-channel event timing are especially needed.

Narrow-band holographic filters for SLR

Moshkov V.L.
IPIE, Russia
E-mail: natalia.n@g23.relcom.ru

A brief review of modern narrow-band holographic filters and their fabrication technology is presented. The new filters have parameters equivalent to ones of state-of-the-art double monochromators. The technological process used for fabrication is described.

Applications of Riga Event Timer at Shanghai SLR

Zhang Zhongping¹, Yang Fumin¹, Zhang Haifeng¹, Wu Zhibo¹, Chen Juping¹, Yu Artyukh²
1 Shanghai Astronomical Observatory, Chinese Academy of Sciences, China
2 Institute of Electronics and Computer Science, Riga, LATVIA
E-mail: zzp@shao.ac.cn

Poster:
The Shanghai SLR station is the first one in China to choose the Riga A032-Event Timer for its advanced performance and better price. After that, several stations in China also use the Riga A032-Event Timer. The paper presents the applications of Riga A032-Event Timer to routine SLR, high repetition rate SLR and Laser Time Transfer at Shanghai and Changchun SLR stations. The advanced performance of A032-Event Timer is also shown in this paper.