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The principal scheme of the setup has features that are typical for
multipurpose installations for studying both static (intensity) and dynamic
(time-dependent correlation function) light scattering. The optical
bench and precision goniometer are based on a massive disk. A
He-Ne laser and the focusing system are fixed on the bench.
The receiving system (photo-detecting unit) is located on the
rotating goniometer arm. The thermostat and the cell holder
are coaxial with the goniometer axis. The output signal produced by the
photo-detecting unit is analyzed by a single-board multichannel
correlator which is plugged into a personal computer. The latter performs
data analysis and instrument control. The photo-detecting system consists of
an efficient receiving optical system with the six pinholes turret
for selection of aperture, low-noise photomultiplier tube (PMT)
operating in a photon counting regime, and amplifier-discriminator.
The PHOTOCOR PMT Power Supply unit is housed in a metal grounded
enclosure suitable for panel or table mounting.
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A special fast algorithm has been developed for processing the correlation function. A number of other algorithms are available, to transform the hardware board to the spectrum analyzer, probability distribution analyzer, multichannel counter, etc.
The PHOTOCOR-SP and PHOTOCOR-M correlators can be used
simultaneously on the same computer, for example, when the systems under
investigation contain particles of two significantly different sizes. The
signal from the photodetector is divided and supplied to the inputs of
both correlators. The sample times for the correlators are different (to
cover a selected range of particle sizes) and are chosen in such a way,
that each correlator operates in a real-time mode. Using both correlators,
one obtains a powerful analyzing device that combines the advantages of
each board.
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The PHOTOCOR Complex setup comes standard with the original software package PHOTOCOR Soft which is a powerful and ready-to-use set of programs to control and plan measurement process, and to perform data fitting and analysis. PHOTOCOR Soft provides support to various experimental procedures - from the simplest to the most advanced. If one needs to develop his/her own environment to control measurements and perform data analysis, the code of the library containing some low-level correlator control functions and procedures is also available.
The main window of the default PHOTOCOR Integrated Environment (PIE) is shown below with the four open windows: the Display window to monitor the accumulation of the correlation function, signal intensity changes, and other signal properties; the Control window to set constants and some correlator intrinsic parameters; the Points and Cumulants windows to process accumulated and read data, and display fitting results. To simplify measurement control and data analysis, the PIE has its own built-in command interpreter to create and use various sets of commands that together accomplish an assigned task. The interpreter includes all possible commands that may be accessed via PIE menu or dialog boxes (e.g., correlator control, setting constants, etc.)
An extremely important feature of the correlator board is that it accumulates data by itself, after all necessary initializations have been done, without interfering with most program operations, so that the program may be quitted, or be used to process previously saved data files. With the innovative reporting capabilities of the PHOTOCOR Soft, one can create, modify, and print experimental reports. The PIE can be used fruitfully as a part of a larger arrangement project due to the poss ibility of exchange of dynamic data with other applications. A user can install his/her own routines of raw data interpretation directly to the PIE. With the powerful customizing features of the PHOTOCOR Soft, one can configure how the output information is formatted and what information appears. A complete on-line context-sensitive help that can be used without interrupting the work in the PIE is provided. The help on the keyboard as well as on selected commands, open dialog bo xes, or messages is available, or can be browsed through as a general reference.
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