Lasers meet changing demands of biomedical applications

Fluorescence detection techniques for applications such as cytometry, microscopy, and sequencing continue to advance with support from evolving laser sources such as optically pumped semiconductor lasers, which provide a range of wavelengths and powers. In flow cytometry, cells are tagged with fluorescent probes and are passed through the interaction zone, where laser beams excite fluorescence. The signal from each cell is separated into several wavelength bands by dichroic beam splitters, prior to detection. A key trend in research instruments is the increasing use of ultraviolet (UV) lasers to excite endogenous (natural) fluorescence and/or for expanded multicolor analysis/acquisition. Optically pumped semiconductor laser (OPSL) technology is excellent for generating true-CW ultraviolet because it is does not suffer from green noise. The reason is that the upper state lifetime of the semiconductor gain medium is considerably shorter than the round trip time of the laser cavity, so there is no stored gain to support dynamic mode competition. While Ti:sapphire lasers continue to be the workhorse sources for multiphoton microscopy, femtosecond lasers based on ytterbium technology have recently gained popularity. Used directly at their wavelength of 1055 nm, they excel in activating red-shifted fluorescent proteins, photoactivators, and Ca indicators.