Detectors For Spectroscopy: UV Through Mid-Infrared

Choosing a detector for a spectroscopic instrument involves more than matching a wavelength range. The detector must deliver the right combination of spectral coverage, noise performance, speed, linearity, dynamic range, and stability for the measurement.

This application note from Opto Diode provides a practical guide to detector selection, specification, and front-end design across wavelengths from approximately 1 nm to 5 µm. It explains how different detector technologies map to specific spectral bands, from windowless silicon devices for soft X-ray and vacuum UV applications to silicon photodiodes for visible and near-infrared measurements and lead salt photoconductors for short- and mid-wave infrared.

The note also examines the electrical specifications that can determine real-world instrument performance. Responsivity, capacitance, rise time, noise equivalent power, detectivity, time constant, and element resistance each affect how a detector performs within a complete spectroscopic system.

Beyond detector selection, the application note addresses front-end electronics, including transimpedance amplifier design for photovoltaic detectors and bias, chopping, and signal recovery for photoconductive devices. It also explores practical issues such as out-of-band response, stray light, cooling, and differences between dispersive and Fourier transform instrument architectures.

For designs that require something beyond a catalog component, Opto Diode also discusses custom detector options, including active area and geometry, packaging, integrated filtering, and matched detector-emitter pairs.