An atomic absorption spectrophotometer consists of a radiation source, an atomizer, a monochromator, and a detector.

The radiation source usually has a narrow range, like a hollow-cathode lamp, or HCL, or an electrodeless-discharge lamp, or EDL. Instruments with continuum sources uses very high-resolution monochromators.

Next is the atomizer, with common methods being flame atomization and electrothermal atomization. 

Some atoms get thermally excited and emit radiation. This interference can be isolated by using a mechanical chopper between the source and atomizer to give the emissions caused by the source radiation a distinct, constant-frequency pattern.

In a single-beam spectrophotometer, the radiation passes directly through the atomized sample.

A double-beam instrument splits the source beam. One beam passes through the atomized sample, while the other bypasses it. Then, the two beams recombine using a half-silvered mirror.

Afterwards, the beam passes through the monochromator, which sends only a narrow wavelength range to the detector—typically, a photomultiplier tube, which converts light into amplified electrical signals.