Detector

Consists of semicylindrical cathode and a wire anode sealed in evacuated transparent envelope o Surface cathode – photoemissive coating, emits electrons upon being irradiated

Photoemissive coating, emits electrons upon being irradiated

More sensitive than photodiode o Dynodes – maintained at increasing potential on which an accelerated electron produces several additional electrons o Sensitive to UV-Vis radiation; extremely fast response; house in light-tight compartment

Most common light detector used in instrumentation o p-n junctions – produces hole-electron pairs when irradiated

Maintained at increasing potential on which an accelerated electron produces several additional electrons

Based on photoconduction – promotion of electrons to energy states where they can conduct electricity o PCTs consists of a thin film of a semiconductor material such as PbS, mercury cadmium telluride (MCT), or indium antimonide o Useful for MIR and FIR regions

Array of photodiode elements (64 to 4096) o Enable detection of several wavelengths o Detectors used in multichannel instruments o Lower sensitivity, dynamic range, and S/N compared to PMT

Produces hole-electron pairs when irradiated

Consists of a conducting element whose electrical resistance changes as a function of temperature; fabricated from thin strips of metal such as nickel or platinum or from semiconductors consisting of oxides of nickel or cobalt (thermistors)

Manufactured from crystals of a pyroelectric material, such as barium titanate or deuterated triglycine sulfate o Produces a temperature dependent voltage when exposed to IR radiation

Consists of small cylindrical chamber that is filled with Xe and contains a blackened membrane to absorb radiation and heat the gas

Consists of one or two pairs of dissimilar metal junctions that develop a potential difference when their temperatures differ; magnitude of potential difference depends on the temperature difference between metals

An electronic device that amplifies the electrical signal from the detector ▪ May alter signal from dc to ac (or reverse), change the phase of signal and filter it to remove unwanted components ▪ May also be used to perform mathematical operations on the signal (differentiation, integration, conversion to a logarithm)

Device that restricts the radiation being measured to a narrow band that is absorbed or emitted by the analyte (effective bandwidth or spectral bandpass)

Can be in form of a digital meter, recorder, CRT, computer monitor, deflecting needle, etc)

Consists of a colored glass plate that removes part of the incident radiation by absorption; rugged, low cost, suitable for VIS region. Effective bandwidth – 30-250 nm; low transmittance

Consists of a thin layer of a transparent material (CaF2 or MgF2) coated on both sides with a film of metal that is thin enough so that it emits approximately half of the radiation striking it and reflects the other half.

Converts EMR energy into electrical energy (voltage, current or charge)

No exit slit

Multiple exit slits

Cheaper to fabricate o Provide better wavelength separation o Disperse radiation linearly

A major advantage of gratings over prisms is that, in contrast to a prism, the dispersion along the focal plane is for all practical purposes linear.

Based upon the heating effect of radiation ▪ Useful for measurement of IR radiation ▪ Converts heat energy to electrical energy

Based upon the interaction of radiation with a reactive surface to emit electrons resulting in the development of a photocurrent or to promote electrons to energy states in which they can conduct electricity (photoconduction) ▪ Useful for detecting UV, VIS, and NIR but not IR and longer wavelengths (except MCT)

Operate by absorbing all but a restricted band or radiation from a continuous source