The history of the external as well as the internal photoeffects in solids is closely connected with the development of quantum-mechanical foundation of electronic states in solids and of interaction of light with matter. Paul Goerlich entered science with the invention of the cesium antimonide photocathode in 1936. Combining the experience of early semiconductor physics in Germany with the feeling of an industrial manager for maturity of results for application in measurement, Goerlich became an active promoter of the physics of photoeffects both as an author and as an active member of IMEKO. The state-of-the-art of the photoeffect physics at the time when Goerlich began his career, when he was active as a teacher and editor as well as after that time, will be outlined. Typical concepts will be ordered into the scientific and technological context. The exciting new possibilities of artificial microstructures will open new applications.
In the past, fundamental radiometry with primary radiator standards was based on the realization of Planck's radiation law by high temperature blackbody radiators, and was therefore restricted to the spectral regions of the ir, the visible, and the near air uv. Today, radiometry is developed in a broadly extended spectral region using synchrotron radiation calculable according to Schwinger. Spectral photon fluxes generated by the primary radiator standard BESSY have uncertainties from 0.6% in the x-ray region (photon energy 15 keV), down to 0.2% in the visible and near ir (photon energy 1 eV). Up to the end of this decade, PTB intends to realize radiometric units at least from 1 eV to 100 keV by use of BESSY I and II. Undulator radiator standards will entail further progress in radiometry of vacuum uv and soft x-ray radiation for photon energies <EQ 1 keV.
We have developed a new photometer by which spectral flux measurements are possible down to 180 nm nearly independent of size and shape of the UV lamp to be measured. The method consists in measuring and adding spectral irradiances on an envelope surface which surrounds the lamp. Lamp radiation is received by a special fiber optics and coupled into a fast array spectroradiometer. Measurements can be performed in an inert gas atmosphere.
Specialized instrumentation is being developed at the National Renewable Energy Laboratory (NREL) for the measurement of both outdoor and simulated solar radiation. Examples include the Atmospheric Optical Calibration System (AOCS), solar ultraviolet (UV) spectroradiometers, and spectroradiometers for measuring spectra of pulsed solar simulators used in the testing of advanced solar photovoltaic devices.
Kinetics and magnitude of integral flow of thermal radiation excited by laser beam in semiconductors and metal-semiconductor structures are measured. It is shown that such measurements allow one to control surface properties of a semiconductor, to determine a velocity of surface carriers recombination, to reveal near-surface macrodefects, to define the quality of metal-semiconductor interface, etc., and, in addition, to draw conclusions about the conditions and mechanisms for laser-stimulated processes of diffusion, defects creation, p-n junction formation, and other processes of laser modification of semiconductor structures.
For the past quarter century, photodiode arrays, or solid-state image sensors, have made tremendous progress, as well as memories and micro computers, owing to advances in the silicon technology. They have taken the place of TV image pick-up tubes, because they have advantages of small size, low power consumption, high fidelity, low noise, and high sensitivity. At present, solid-state image sensors, especially charge coupled devices (CCD), are widely used, both in home-use video cameras and broadcast-use video cameras. There are a lot of important inventions and improvements to realize practical solid-state image sensors ; Large scale photodiode arrays need an on-chip scanner, because not as many output terminals can be prepared as the number of photodiodes. The first self-scanned photodiode array was " Scanistor", reported by Horton in 1 964 . In 1970, Boyle and Smith invented a remarkable low noise scanner, called the charge coupled device (CCD) 2, The integration mode in photodiodes for obtaining high sensitivity was proposed by Weckler in 1967g. Around 1973, the basic structure for the present CCD image sensor was made up. After that, the characteristics were improved, as the pixel number was increased. Blooming, which is an overflow of excess charge due to large incident light, is suppressed by the vertical overflow drain (VOD) structure4. Image lag suppression and dark current reduction are achieved by the pinned photodiode5. Progress made in solid-state image sensors is still remarkable, as well as that in memories and microprocessors. Image sensors supply various kinds of information, taken from images. Images, or scenes, themselves have an intensity profile as a function of space coordinates, x, y, z, time t, and light wavelength . "Light" usually means visible light, but includes all electromagnetic waves, such as infrared, millimeterwave, ultraviolet, and X-ray. Since all physical variables, such as supersonic, magnetic field and so on, have a profile, they provide an image as well as light. In this paper, visible light is mainly dealt with. Image sensors can take specific information from an image, and show it on the reproduced picture. The luminance signal supplies shape, size, number, and position. The chrominance signal gives color. Motion information can be obtained from a set of reproduced pictures, taken in a small time interval. 3-dimensional image reproduction can be obtained by using plural cameras. Furthermore, pattern recognition and identification are realized by image processing technology. To provide this information, the most important thing for image sensors is to take an image with high fidelity. For this purpose, much research and development are still being carried on.
After the description of the detectors used as standards for radiometric measurements at the Institut National de Metrologie (INM) and the designation of their range of use, the method which is used to calibrate the transfer standard detectors, for the measurement in the field of optical fiber telecommunications is described. This method is divided in four successive steps. To finish with, the study of the main components of the uncertainty budget is done.
This paper presents a new approach to the broadband filter method for spectral responsivity measurements. The mathematical formulation, taking into account a some a priori knowledge of the spectral responsivity to be measured, allows one to overcome most of the drawbacks still present in this method. Some simulated and experimental tests on the measurement of V((lambda) )-corrected detectors show the capabilities of the proposed approach.
Analysis of the dynamic time response of a solar element or other photovoltaic devices after a pulse illumination gives more details of microphysical processes and inherent parameters. By means of different types of investigations one can separate diffusion and lifetime effects. Using different wavelength of irradiation, the influence of back side contact effects is to analyze with respect to the optical and recombination properties. Because the capacitance of the depletion layer and the concentration of acceptors is included into the registrated voltage decay, both parameters can also be determined. Measurements were made by using excimer laser radiation of 308 nm wavelength and 10 ns duration or dye laser radiation within a spectral range from 500 nm to 700 nm. The available radiation flux density was in a range from 10 mW/cm2 to 100 W/cm2. The irradiation was applied at front or rear side of commercial solar cells. Mono and poly crystalline material were investigated. The transient responses in short circuit current and open circuit voltage was registrated with a high speed DSO. For analyzing the physical processes, a numerical simulation of the cell has been developed. This modeling allows to study the fundamental effects and their time evolution step by step. Values for different parameters can be obtained by a mathematical fitting procedure. The results of various samples will be shown and discussed.
This paper presents possibilities for higher precision in photometric laboratories in the daily calibration work. Since a number of national laboratories verify the basic quantity, the candela, by the use of a lamp, geometrical errors in the setup are often made. This increases the error of reproducibility. A simple, but special setup using a standard lamp - lampholder - mirror unit together with a laser system, is introduced. This system is also useful for adjusting and calibrating Goniophotometers as well as for the work on photometer benches.
A new Standard Reference Material set has been developed at the National Office of Measures Hungary. The set includes six neutral absorbing glass filters for linearity measurements having optical densities 0.5 - 4.0, one cut-off filter for checking stray light and a didymium filter for wavelength calibration. A new method has been developed for high accuracy (< 0.06 nm) wavelength calibration. This accuracy was demonstrated at eight wavelengths during the past five years. The method is practically independent of bandwidth for spectrophotometer with bandwidths less than 10 nm.
Color measurement techniques are discussed, comparing chromaticity coordinate values obtained by two different methods. Tristimulus (TS) colorimeters based on detectors matched with specialized filters exhibiting response curves like the CIE color matching functions are simpler and yet useful tools for most industrial applications. Limitations in their applicability is also shown.
DC substitution methods are used for the measurement of a wide range of physical parameters across the whole electromagnetic spectrum. A summary is given of the principles involved with a view to alerting users of such techniques in the area of optical radiation measurement to related work in other areas of metrology. Because of the similarity of the methods, much useful information and insight can be gained from such a wider perspective. This applies to both the striking similarity of the techniques and the analysis of required instrumental corrections.
The spatial variations of surface reflectance and response of a number of silicon photodiodes has been measured at wavelengths between 325 nm and 633 nm using a measurement spot size (1/e2) of approximately 50 micrometers . The surface reflectances have been modelled using ellipsometrically determined SiO2 layer thicknesses and compared with spectrophotometric measurements. Also the reflectance variations across the diode surface have been correlated with the response variations to give a measured of the spatial internal quantum efficiency uniformity for each photodiode.
In using silicon integrated-circuit technology now, we have developed a new detector for the absolute measurement of radiation fluxes by combining a thin-film thermopile with a (meandered) heating element arranged within the receiving area system following our former thin-film absolute radiometer conception from 1980. The sensing junctions and legs of the thermopile and the heater are supported on a thin Si3N4/SiO2 membrane formed by anisotropic etching of the Si base material. The multijunction thin-film thermopile is fabricated from BiSb and Sb in a multilayer technique by microlithographic methods. The 76 sensing junctions are arranged on the periphere of the receiving area 7 mm in diameter. The membrane and chip dimensions are 8 X 8 mm2 and 12.5 X 12.5 mm2, resp. It is intended to minimize both the temperature coefficient (TC) of the responsivity and of the calibration of the device. First measuring results of responsivity of the detector, its TC, linearity, time constant and the local distribution of responsivity are represented and possibilities are shown to improve these parameters by choosing appropriate materials for the heater as well as the thermopile.
In this paper we will describe an electrically calibrated radiometer, based on PVF2 pyroelectric detector, for absolute pulsed laser energy measurements. The original approach used is fundamentally quite different from those previously used for power measurement. A theoretical study of the difference between the electrical and radiative mode allows us to determine the correction factor that must be applied to the measurement.
This paper reports the results of laser beam attenuation measurements for a u.v. transmitting fiber in terms of the pulse energy and wavelength. The investigation was carried out in view of the fact that all-silica u.v. fibers may have an important role to play in the evolution of new spectroscopic techniques such as Resonant Laser Ablation. The advantages and disadvantages of employing this type of fiber within a high power laser-based system must be clearly established by characterizing the attenuation properties of the fiber experimentally within the required operating ranges of wavelength and pulse energy (i.e. launch energy).
A polarimetric interferometric based pressure sensor, using a photoelastic material as a sensing element is demonstrated. The light source used was a multimode laser diode, coupled into the system through a highly birefringent fiber to provide a reference bias signal. The arrangement of the sensor system produces birefringence in the sensing element, and a Michelson interferometer to which the light then passes is used for signal processing. The path difference induced by the pressure was measured by re-establishing the interference condition in this Michelson interferometer. The pressure to be measured was applied by placing a calibrated mass on the sensing element. Results are presented showing the potential of such a system for pressure sensor applications.
The measurement of actinic UV-radiation will be most precisely realized by the spectroradiometric method. The spectral measurement quantities are evaluated numerically with weighting functions. But laboratory devices are not transportable. Outdoor measurements and measurements at working places are possible with the developed equipment with an acceptable accuracy.
In this communication we describe an optical non contact microtopographer that we developed and are presently expanding and improving. The system is based on a simple triangulation procedure: the topographic information is obtained from the horizontal shift incurred by the bright spot created, by an oblique light beam, on a surface when it is displaced vertically. A laser beam is focused onto a small, diffraction limited, spot on the surface and is made to sweep it. The horizontal position of the bright spot is perpendicularly imaged onto a linear CCD array and the information about the individual detectors that are activated, above a certain controllable intensity threshold level, is used to compute the corresponding horizontal shift on the reference plane. Simple calculations allow us to obtain the distance between the surface and a reference plane at each sampled point and so a map of the surface topography can be built statistic surface characterization parameters may be calculated. We will also show that this kind of triangulation based surface inspection system can be applied not only to large distance range sensing, but also to smaller samples or smother surface with resolutions that can be driven down to the sub micron range.