Chapter 7

Components of Optical Instruments

Components of Optical Instruments

Typical spectroscopic instruments contain five components: (1) a stable source of radiant energy, (2) a transparent container for holding the sample, (3) a device that isolates a restricted region of the spectrum for measurement, (4) a radiation detector that converts radiant energy into a signal detector, (5) a signal processor and readout.

Components of Optical Instruments

AbsorptionFluorescencePhosphorescenceScatteringEmissionChemiluminescence

Rayleigh & Raman Scattering Occur when the dimensions of the particles that

cause the scattering are small in comparison to the wavelength of the incident radiation. Dissolved particles can result in Rayleigh and Raman scattering.

A type of Raman Spectrometer: FRA 106/S Spectrometer

Sources of Radiation

RequirementsSufficient powerStability over long periods of timeVoltage regulation required as radiant

power varies exponentially with voltage

Lasers

LasersPumpingSpontaneous emission (fluorescence)Stimulated emissionAbsorption

Wavelength SelectorsFilters Interference Filters Interference Wedges Absorption Filters

Wavelength SelectorsMonochromators- one color - pass a narrow band of

wavelengths

The SURE_SPECTRUM is an imaging spectrograph and scanning monochromator that features dual exit ports for maximum flexibility.

Wavelength Selectors

View of inside of monochromator

Wavelength Selectors

Radiation Transducers

Photomultiplier

Radiation Transducers

Photodiode Arrays (PDA)

Radiation Transducers

Charge Transfer DevicesCharge Injection Devices (CID)Charge-Coupled Devices (CCD)

Signal Processors & ReadoutsPhoton Counting

Advantages: Improved signal-to-noise ratio Sensitivity to low radiation levels Improved precision for a given measurement time Lowered sensitivity to photomultiplier tube voltage

and temperature fluctuations Detection method of choice in fluorescence,

chemiluminescence, and Raman spectrometry

Signal Processors & ReadoutsPhoton CountingDisadvantages: Required equipment is

more complex and expensive

Technique has not been widely applied for routine molecular absorption measurements in ultraviolet and visible regions

Principles of Fourier Transform Optical Measurements Transforms data set from time domain to frequency

domain Advantages

Throughput High resolving power

Interferometers Michelson Mach-Zender Fabry-Perot

References www.anachem.umu.se/jumpstation.htm www.anachem.umu.se/cgi/jumpstation.exe?AtomicSpectroscopy www.anachem.umu.se/cgi/jumpstation.exe?OpticalMolecularSpectroscopy www.minyos.its.rmit.edu.au/~rcmfa/mstheory.html http://science.widener.edu/sub/ftir/intro_it.html http://www.s-a-s.org/ http://www.chemsw.com http://www.scimedia.com/chem-ed/spec/atomic/aa.html http://www.chemistry.msu.edu/courses/cem333/Chapter%207%20-%20Components

%20of%20Optical%20Instruments.pdf http://www.brukeroptics.com/ http://laxmi.nuc.ucla.edu:8248/M248_99/autorad/Scint/pmt.html http://www.spectralproducts.com http://www.parallax-tech.com/twotubes.htm http://www.thespectroscopynet.com/Educational/Gratings.htm http://micro.magnet.fsu.edu/primer/digitalimaging/concepts/ebccd.html http://www.cerncourier.com/main/article/43/2/7/1/cernnews9_3-03