Image of Flex99R-FCS-12, external enclosure not shown in this picture.
Introduction:
Flex99R-FCS-12 is designed to operate in one of the two modes. In photon correlation mode, it works like an ordinary fast (12.5ns) multiple tau correlator. It calculates the correlation function in real time covering delay times from 12.5 ns to about an hour with 288 data points. In photon history recorder mode, it records the time between successive photon events. This is measured by counting the number of ticks of the system clock between the photon events. This time is then transfered to the host personal computer via high speed Universal Serial Bus (USB). The amount of information to be transfered is proportional to the count rate of the incoming photons. Using a lossless compression technique, Flex99R-FCS-12 transfers complete time series without gaps for average count rate from 0 to 1.6 Mcps.
Flex99R-FCS-12 hardware specifications:
- Input signal: standard TTL pulses.
- Two BNC connectors
- One USB connector.
- Easy to use FlexWindows software and software for Windows98 libraries included.
Correlation mode specifications:
Multiple tau channel layout ( sample time denoted at T, data width W):
- Auto/cross correlations.
- 12.5 ns minimum sample.
- 288 real time channels.
- Delay time range: 12.5ns to 1 hour in multiple tau channel layout.
- First 16 channels: T = 12.5ns, W = 1 bits, delay times T to 16*T;
- Second 8 channels: T = 2*12.5ns, W = 2 bits, delay times 9*T to 16*T
- Third 8 channels: T = 4*12.5ns, W = 2 bits, delay times 9*T to 16*T;
- Fourth 8 channels: T = 8*12.5ns, W = 3 bits, delay times 9*T to 16*T;
- Sample time doubles every 8 channels and data width increment 1 bit to prevent overflow.
- The longest delay time is about one hour.
Intensity limits in Correlation mode:
Flex99R-12 is designed with sufficient hardware resource to prevent overflow at any reasonable intensities. However, in extreme situations, clipping and overflow could happen. The intensity limits are following:
- Maximum intensity integrated over 50ns: 60 MHz. Overflow will happen if the input intensity exceeds the maximum.
- Maximum intensity integrated over 168ms: 28.3MHz. Overflow will happen if the maximum is exceeded.
Photon history recorder mode specifications:
- System clock: 60 MHz.
- 16.7 ns pulse pair resolution.
- Complete time series recorded on a PC hard drive for average count rate up to 880 KHz in one channel mode.
More about multiple tau theory.
Multiple tau theory was invented by Klaus Schätzel. The following papers discuss the theory and the advantage of the multiple tau scheme.
- Klaus Schätzel. Single Photon Correlation Techniques. Dynamic Light Scattering: The method and some applications, Edit by Wyn Brown, Clarendon Press, Oxford, P 76, 1993.
- Klaus Schätzel et. Noise on Multiple-Tau Photon Correlation Data. SPIE Vol. 1430, P109, Photon Correlation Spectroscopy: Multicomponent Systems, 1991.
- Klaus Schätzel. New Concept in Correlator Design. Inst. Phys. Conf. Ser. No. 77, P175, 1985.
- Klaus Schätzel et. Photon Correlation Measurements at Large Lag Times. Journal of Modern Optics, Vol. 35, No. 4, P711, 1988.