Kinetics Spectroscopy

• Full 16 Bit Dynamic Range
• > 3 µsec Time Resolution
• Ultra Low Noise Readout
• Fully Supported by WinSpec Software

When the Kinetics Spectroscopy detector is used with an imaging spectrometer and an Optical Fiber Adapter, the user can direct light delivered to the spectrometer either to the open row at the top of the chip for operation in kinetics mode or to the bottom of the array for conventional spectroscopy.

The spectral readout of scientific low noise CCD detectors is generally limited to 10 spectra/second. To capture spectra with each one corresponding to as little as 3 microseconds acquired in a burst (corresponding to a burst spectral rate of 300,000 spectra/second) while still offering a full 16 bit dynamic range, Princeton Instruments utilizes the Kinetics Spectroscopy readout mode. The CCD is masked in a special way. By leaving only one row open near the top, spectra acquired in this one row can be shifted under the mask at high speed and stored for later readout. Up to 250 spectra can be stored in a single burst. Readout is then at traditional "slow scan" low noise rates. To add to the flexibility of this system, there are also 100 rows left unmasked at the bottom of the CCD. This offers a 2 mm area of the CCD that is available for conventional non-kinetics spectroscopy. Thus when this detector is used with an imaging spectrometer and an Optical Fiber Adapter, the user can direct light delivered to the spectrometer either to the open row at the top of the chip for operation in kinetics mode or to the bottom of the array for conventional spectroscopy. A special mask over the 100 open rows can be provided for experiments with non-imaging spectrometers and when the detector will only be used in the kinetics mode. The masking is directly on the silicon of the CCD, necessary for obtaining single row illumination with no inter-row crosstalk (lower than 0.1%). In kinetics mode operation, the CCD retains its full well depth at burst rates of up to 10 microsecond/spectra. Faster operation at down to 3 microseconds/spectra results in a 40% loss in well size, and reduction of dynamic range to slightly less than 16 bits when read out with 5-6 electrons read noise. Except in cases of transient light sources, a fast shutter is required to exclude light both prior to the high speed burst of spectra and afterwards. An image intensifier can be coupled to this system via PI’s optimized lens coupling. If the detector is coupled to an image intensifier, the intensifier used should be one with a rapidly decaying phosphor, to avoid loss of time resolution. One of the many advantages of the SPEC-10 system is the flexibility of the detector controller. Under complete software control, the detector controller can customize the readout of the CCD. These readout modes allow much higher frame rates than would normally be possible with full frame readout. By combining customized readout with binning in both the slit and spectral dimensions frame rates in excess of 1000 spectra per second are achievable.

High frame rate spectroscopy does not require any modifications to the hardware of the SPEC-10 or its controller. The only physical modification required is the masking of the image area of the CCD. This can most easily be accomplished by positioning the fiber input to the spectrograph such that the fiber image falls on the bottom portion of the CCD image area, or by masking the top portion of the entrance slit of the spectrograph to leave only the bottom of the CCD image area exposed. Note: any light that falls on the unused portion of the image area will show up in subsequent spectra.

Example of illumination of the CCD image area to perform very high frame rate spectroscopy.

The WinSpec software has full access to the way that the controller reads out the camera and can take advantage of the limited illumination of the CCD. Now that all of the spectral information is contained in the bottom portion of the CCD, it is no longer necessary to read out the top portion of the CCD. By reducing the number of active rows used during readout, a substantial saving in readout time can be realized. This customized readout mode is not the same as simply selecting a region of interest. Instead, it is more akin to creating a new detector with a reduced image area. The ultimate spectral frame rate will depend on the readout time and the exposure time. The readout time can be viewed from the Acquisition Menu. The exposure time can be set from Main Tab of the Experiment Setup Window (an exposure time of 0 is valid). Readout times for a few customized readout modes are listed in the following table.