A spectrometer measures light properties across specific electromagnetic spectrum ranges, aiding in material identification.
Key components include the source, wavelength selectors, and detectors.
1) Sources of Radiation:
Provide stable, long-lasting IR radiation over the desired wavelength range.
Globar: Silicon carbide rod emitting in the mid-IR region; stable spectral radiance.
Nernst Glower: Ceramic rod made of rare earth oxides; emits in the mid-IR, with radiance increasing with wavelength.
Tungsten Filament: Covers near-IR and visible regions with broad emission.
Mercury Arc Lamp: Emits radiation in the far-IR region.
2) Wavelength Selectors:
Separate broad-spectrum radiation into specific frequencies.
Monochromators: Use prisms or gratings to disperse radiation by bending different wavelengths differently.
Interferometers: In FTIR instruments, they split and recombine beams to produce an interferogram, which is Fourier transformed to generate the spectrum.
3) Detectors: (Instrumentation in infrared (IR) spectroscopy)
Convert transmitted or reflected IR radiation into an electrical signal for analysis.
Golay Cell:
Thermal detector using gas pressure changes due to IR heating.
Application: Wide frequency range, fast response (used in FTIR).
Bolometer:
Detects resistance changes in blackened platinum or gold strips upon IR absorption.
Application: High sensitivity for far-IR detection.
Thermocouple:
Two joined metals produce a voltage when heated by IR radiation.
Application: Moderate sensitivity, suitable for mid-IR.
Thermistor:
Semiconductors whose resistance changes with temperature upon IR exposure.
Application: Higher sensitivity for mid-IR.
Pyroelectric Detectors (e.g., DTGS):
Generate voltage with temperature changes due to IR heating.
Application: Broad spectral response, ideal for FTIR instruments, operates at room temperature.
These components collectively ensure precise and reliable IR spectroscopic analysis across various applications.