Sampling Gate Research Articles

High-speed optoelectronic sampling with semiconductor-laser pulsed coplanar photoconductor

A semiconductor-laser strobed photoconductive sampling gate for the measurement of ultra-high-speed electronic signals on coaxial lines is reported. For the short response (<100 ps) and high responsivity (>0.1 A/W) at the 830 nm laser wavelength the sampling gate uses a miniaturised (8×8×1 μm) epitaxial GaAs photoconductor on a broadband tapered coplanar 50 Ω microwave structure.

Time-Resolved Spectral Measurement in Hollow Cathode Discharge Tubes by Photon-Counting Method

A microcomputer-controlled photon counting system using a digital sampling method has been developed to perform the spectral measurement of weak lines emitted from Ne atoms and ions excited by square-wave voltage pulses in hollow-cathode discharge tubes with sufficient sensitivity and accuracy. The characteristic features of the system are, 1) the high-voltage pulse generator and photon counter are operated synchronously, 2) the background noise and dark current of the photomultiplier are effectively eliminated by the use of two sampling gates, 3) even when the scanning range is greatly expanded, fluctuation of the gate position remains small. It has been observed using the system that the rise time of the intensity of a neutral line of Ne is generally shorter than that of an ionic line in pulsed hollow-cathode discharge.

Picosecond AlxGa1−xAs modulation-doped optical field-effect transistor sampling gate

New modulation-doped Alx Ga1−xAs/GaAs metal-semiconductor field-effect photodetectors have been fabricated and tested in a novel picosecond optical sampling gate configuration. The rise time was measured to be 12 ps, with a full width at half-maximum of 27 ps. The optical electronic picosecond cross-correlation measurement has shown the importance of the two-dimensional electron gas for high-speed operation.

Impulse response of photoconductors in transmission lines

The response of high-speed photoconductors to picosecond optical pulses is analyzed by representing them as time-varying circuit elements in transmission lines. Expressions are derived for transmitted and reflected waves for photoconductors used both as pulse generators and sampling gates. These results are then used to determine the correlated response of pairs of photoconductors in different transmission line networks. The results provide a basis for estimating the limiting speed of response of this approach to very high-speed electronic measurements.

Photo-Induced Current Transient Spectroscopy in High-Resistivity Bulk Material. II. Influence of Non-Exponential Transient on Determination of Deep Trap Parameters

Computer simulation and experimental study on the influence of non-exponential current transient upon the determination of the trap-activation energies and the capture cross sections in PICTS have been performed. The condition of sampling times t1 and t2 (t1<t2) should not be such that t1 is fixed and t2 is varied since large errors are introduced into the obtained trap-parameters, while the condition that t2/t1 is fixed and both t1 and t2 are varied, should be used in order to minimize the errors. By using a computer controlled multi-channel PICTS system which has a large number of sampling gates, the experimental study on the influence of non-exponential transient upon PICTS in a high-resistivity bulk CdS single crystal has been made possible. The results obtained experimentally in the bulk CdS for the non-exponential case have been found to agree well with the predictions of the simulation.

Picosecond signal sampling and multiplication by using integrated tandem light modulators

A picosecond signal sampling experiment was performed successfully by using integrated optic technologies. Two interferometric modulators of the traveling-wave and lumped types were integrated in series on a LiNbO 3 crystal surface. The traveling-wave modulator was oprated as a sampling gate activated by an electrical pulse train of 1-GHz repetition from a comb generator, while the lumped one was driven by a 2-GHz CW signal. The aperture time of the gate was estimated about 52 ps from the measurement using the image tube streak camera modified to sinusoidal scan at 1 GHz. Also a signal multiplication experiment was carried out using 100- and 10-MHz CW signals.

Picosecond optical electronic sampling: Characterization of high-speed photodetectors

A photoconducting sampling gate which is triggered by a picosecond optical pulse and has an aperture of approximately 12 ps has been used to measure accurately the response of a high-speed, solid-state photodiode. The sample gate, which is made from a radiation-damaged semiconductor, is demonstrated to have better speed, lower noise level, negligible jitter, and fewer reflections than conventional sampling oscilloscopes. In addition, it can be used over a wide temperature range by direct mounting in a variable temperature cryostat.

Sea‐state‐related altitude errors in the SEASAT radar altimeter

For the work reported here, a six‐parameter model waveform is least squares fitted to 10‐s averages of the data from the 63 waveform sampling gates in the SEASAT radar altimeter. One of the fitted parameters is a time‐origin parameter that provides a measure of the position of the actual mean radar waveform relative to the sampling gate set and thus provides a correction to the instrument's altitude measurement. For the data set analyzed this correction appears to vary quadratically as a function of the significant waveheight (SWH). The result to date is that the correction ΔG, in centimeters, which should be added to the surface elevation measurements on the SEASAT geophysical data record (GDR), is given by ΔG = 0.593 SG + 0.476 SG2 where SG is the GDR value for SWH, in meters. The discussion in this paper reviews waveform assumptions built into the SEASAT onboard altitude tracker and subsequent altitude data processing and lists several additional important effects that were not included in that processing but which are incorporated into the SEASAT waveform analysis reported here.

Measurement of GaAs field-effect transistor electronic impulse response by picosecond optical electronics

Direct time-resolved measurements of the linear and nonlinear electronic impulse response of a high-speed gallium arsenide metal semiconductor field-effect transistor have been made by using picosecond optical pulses to drive high-speed photoconducting electronic pulse generators and sampling gates. High resolution, jitter-free measurements with excellent signal-to-noise showed the field-effect transistor to have a fast full width at half-maximum response of approximately 25 ps, and a slower fall time of 75 ps.

Noninvasive assessment of aortocoronary bypass graft patency using pulsed Doppler echocardiography

To evaluate noninvasively aortocoronary bypass graft patency, pulsed Doppler echocardiography was performed at the time of postoperative coronary angiography in 120 consecutive patients. Ultrasonic examination of 163 vein grafts was possible. One hundred twenty-seven patent and 14 occluded grafts were correctly identified. Eleven patent grafts could not be recorded, and 11 occluded grafts were falsely diagnosed as patent. The method had an overall sensitivity of 92 percent and a specificity of 56 percent. This high sensitivity level may be increased to almost 100 percent by enhanced technical skill and experience. The low specificity level, although the method must be tested in a larger number of bypass grafts, stresses the importance of correctly identifying other sources of diastolic blood flow. Diastolic flows from the superior vena cava, internal mammary veins, tricuspid valve, mitral valve and right ventricle may be eliminated by careful adjustment of the depth, site and size of the pulsed Doppler electronic sampling gate. Standard echocardiographic landmarks for avoiding confusion with the coronary arteries are also described.

Decay time measurement of the luminescence of CuCl excited by a picosecond laser

The luminescence of CuCl excited by a mode-locked Nd3+ : YAG laser is studied at liquid-helium temperature. It is recorded through an optical Kerr cell, used as a sampling gate, by an optical multichannel analyzer synchronized to the mode-locked laser. At the excitation intensity used, athe luminescence of CuCl is essentially due to the radiative decay of biexcitons. The decay of this luminescence contains two components, a fast one (τ≃95 ps) followed by a slower one (τ≃450 ps).

A Linear Gate for Sampling

This design presents the principles and circuit of the sampling gate. The design of a bidirectional transistor sampling gate with prescribed specifications is presented. The introduction to the subject precedes a brief resume on conventional samplers The design and circuit implementation is followed by the analysis of the designed circuit. A discussion of stability, thermal runway and accuracy is included. A list of electronic parts used in the design project is also appended.

Subnanosecond Time‐Resolved Spectroscopy of the Biexciton Luminescence in CuCl

AbstractThe biexciton luminescence of CuCl at 4.2 K is studied under intense UV picosecond excitation, and its time dependence is investigated in the range of 0 to 800 ps by means of an ultrafast optical sampling gate. The time‐resolved spectra of the luminescence due to the radiative recombination of biexcitons show a change in shape of this emission band during the first 100 ps, which may be due to the relaxation time of the biexcitons by means of acoustical phonons. A dynamical model, taking into account the collisions between biexcitons and excitons, is proposed, which provides an acceptable fit for the time dependence of the luminescence if a value TM= 1 ns of the spontaneous radiative decay time of the biexcitons is assumed.

A digital trigger delay unit for use in variable-path-length ultrasonic measurements

A digital trigger delay unit is described which automates coherent variable-path-length measurements of ultrasonic velocity and attenuation. The sampling gate of a boxcar integrator is delayed by the device in such a way that it always opens in the same time slot of a progressively delayed received signal. The device has been used in the measurement of velocity and attenuation in gases.

Optically strobed sampling oscilloscope

Describes an optically strobed sampling oscilloscope which uses optical pulses from a GaAs laser diode to strobe a Cr-doped GaAs photoconductor which serves as a sampling gate. This sampling gate has been used with a commercial sampling oscilloscope to provide a sampling measurement capability that can measure higher voltages than conventional samplers and does not exhibit strobe pulse kickout. Preliminary tests indicate a time resolution, limited by the width of the optical pulse used, for about 100 ps.

Electrically strobed optical waveform sampling oscilloscope

A new instrument for measuring optical waveforms is described. It is an optical sampling oscilloscope employing a GaAs photoconductive sampling gate and an electrical sampling strobe. The basic theory of operation is derived. A 100-psec rise-time rudimentary prototype has been built and results of measurements of a GaAs laser diode pulse are presented.

Pulsed-laser application to sampling oscilloscope

An optically strobed sampling oscilloscope is described in which a GaAs laser diode is used to strobe a GaAs photoconductive sampling gate.

Image Analyzer for Electron Microscope

We have recentry developed a unique image analyzer system which combines a scanning electron microscope or a transmission electron microscope with a scanning attachment, and a minicomputer having a 4k-memory. In this system, all measurements and data processings are carried out by computer programs. So, the hardware required for the system consists only of a discriminator, a clock generator, a sampling gate and a computer interface, as shown in Fig.1. Any modification of its function or addition of new functions is performed by software only.

Broad-band thin-film signal sampler

Previous developments in high frequency signal sampling have been extended by applying thin-film and solid state techniques to the sampler design. The basic elements of a sampler are a signal-carrying transmission line, a sampling gate, a drive line for the gate pulse, and a video output. In the design reported here, a thin quartz substrate supports the circuits. To reduce signal-line reflections the gate is made the center element of a low-pass signal-line filter. The gate pulse is developed across a length of slot transmission line in the signal ground plane parallel to and beneath the signal transmission line. A beam-lead Schottky diode pair is mounted across the slot with its center node connected to the signal transmission line through the substrate.

Erratum to : Ultra-High-Speed Photoelectric Spectrometer Using an Image Converter as the Sampling Gate

Erratum to : Ultra-High-Speed Photoelectric Spectrometer Using an Image Converter as the Sampling Gate