A White cell is a type of long path gas phase spectroscopy

Spectroscopy

Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...

cell that is commonly used to measure low-concentration components in gases or liquids. In 1942 John U. White described this concept in the paper Long Optical Paths of Large Aperture
, and since this time it has been known as the White cell or White-design.

Operation

One way to measure low sample concentrations or weak transitions is to employ a multiple-pass cell that will increase the length of the optical path through the cell while keeping the sample volume constant. The White cell achieves this technique by making use of three spherical, concave mirrors that have the same radius of curvature. Figure 1 illustrates a White cell that utilizes four reflective passes to make one traversal of the cell. As shown, the input and output are positioned at the same end of the absorption cell.

Since the mirrors are arranged to minimize optical distortions, the number of passes can be increased many times (in increments of four) to allow for more traversals, thereby making the total optical path length large compared to the volume of the cell. White cells are available with path lengths ranging from less than a meter to many hundreds of meters.