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500 microsecond absorbance
10-3 AU RMS noise over 0.5 milliseconds at 550 nm |
Microsecond Kinetics:
1,000 points per 0.5 milliseconds
The Olis RSM 1000 spectrophotometer is very successfully used in flash and/or laser photolysis work where microsecond detection rates are optimal.
To achieve microsecond data acquisition rates with an Olis RSM 1000, one uses the Olis RSM 1000 in its kinetic mode. This is achieved by replacing the motorized ScanDisk with the fixed slit cartridge.
Options for the RSM Intermediate Slit
Motorized ScanDisk Cartridge
• 1,000 to 1 scan per second.
• 0.5 nm spectral resolution to arbitrary wide.
• Apertures: 16 1 or 2 mm wide slits.
Fixed Slit Cartridge
• Normal speed scanning.
• Microsecond fixed wavelength detection.
• Manually exchangeable slit of 0.1 to 20 mm width.
Motorized ScanDisk can be optimized for fluorescence with the Spoke ScanDisk.
Regular ScanDisk
Spoke ScanDisk
Spoke Scandisk
• Fluorescence rapid-scanning during kinetic experiment.
• Broad spectral resolution.
• Produces the maximum signal strength with some spectral information.
More information...
No other hardware changes are made between millisecond scanning and microsecond kinetics—only the easy to exchange ScanDisk cartridges are replaced one with another.
Kinetics to rates of 20 MHz1 (1000 readings per 50 microseconds) are supported in this mode, opening the way to microsecond detection following flash/ laser photolysis and other high speed studies.
That is, in addition to being able to extract millisecond single wavelength data from the millisecond spectral scans, one can get microsecond kinetic traces from our rapid-scanning spectrophotometer by turning off the rapid-scanning! With the millisecond scanning acility off, and all of the associated high speed electronics and acquisition hardware on, one can acquire kinetic data at microsecond rates.
All kinetic traces can have up to 1,000 points acquired in 50 microseconds (or more slowly). If data are to be acquired across many milliseconds, the twin A/D converter still operates at high speed and data averaging is done during data collection. Thus, heavy over-sampling is occurring, increasing the effective resolution of the 12 bit A/D converter.
Since the spectrophotometer is always operated as a dual beam instrument—even at these 20 MHz rates—one is assured of the best possible kinetic data.(Sample and reference signals are always collected simultaneously.)
Any wavelength within the available spectral range of the RSM monochromator (167-2500 nm) can be monitored at these rates. We recommend taking kinetic traces at multiple wavelengths to build up an ensemble of kinetic traces, thereby "creating" spectral data. That is, multiple traces can be collected as a function of wavelength and stored as an ensemble of traces which can be fitted using GlobalWorks.
In this way, one can do flash experiments as a function of wavelength and take advantage of our superb global fitting software provided in the system.
Owners using the RSM 1000 for laser/flash photolysis work include:
- John Spudich, UT Medical Branch
- James Harmon, Oklahoma State University
- Andy Pacheco, University of Wisconsin
- Robert Birge, Syracuse University
- Tom Wydrzynski, Australian National University
- Daniel Kim-Shapiro, Wake Forest University
- Larry Welch, Knox College
- Kwang-Hwan Jung, Sogang University (S. Korea)
From Andy Pacheco, October 2002, we received this message (he had owned the Olis RSM 1000 for nearly two years at this point): "We have one paper out, and another accepted, both of which show off the OLIS RSM's capabilities very nicely. I have some even more dramatic data, but that won't come out for a few more months...I'm planning to get in touch with your technical guys sometime next week, to get some advice about coupling the start of data acquisition on the RSM with the triggering of a new laser I just ordered."
Conventional Scanning:
just like other scanning spectrophotometers . . . with a twist!
When one takes away the motorized ScanDisk, he takes away millisecond scanning. In place of the motorized ScanDisk, one uses a fixed slit ScanDisk. This single change brings the Olis RSM 1000 spectrophotometer much closer to the operating level of other double grating, dual beam spectrophotometers. Now, like these other spectrophotometers, the gratings are moved to effect scanning. (Recall, in millisecond spectral scanning, there is no time for moving the gratings; hence, the use of our rapidly spinning ScanDisk).
Conventional scanning is available for routine absorbance and fluorescence, i.e,, for those times when rapid-scanning or fastest kinetic modes are not needed. Conventional scanning mode is also the most common mode used with the Olis DSM CD spectrophotometer.
Distinguishing the Olis RSM 1000 as unique among conventional scanning spectrophotometers are our handling of the raw data.
That is, each retained datum within a scan acquired with the Olis RSM 1000 is the fitted result of thousands of readings! Recall, everything in an RSM 1000 is optimized for speed. Thus, whether the ScanDisk is the motorized or fixed slit model, the fast response electronics and PMTs are still used. Thus, data are pouring into the computer at a megabyte per second.
Taking CD as the example, each retained 0.5 second datum is the digital manipulation of one million readings!!
The movement among slow scanning, rapid-scanning, and microsecond fixed wavelength is direct, easy, and quick. All modes are done in dual beam mode, unless one deliberately removes the beam splitter and one of the PMTs.
Learn about the ScanDisk Spoke Wheel and the Fellgett Advantage.
Footnotes
1) 20 MHz is the rate limit imposed by our A/D cards. Some Olis clients have linked directly from the Olis detectors to their own digital oscilloscopes, thereby opening up nanosecond and faster acquisition rates.
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