the characterisation of gold nanoparticles and single-walled carbon nanotube thermopile where a wide tunable range from 400 nm to nm is essential. Tunable sources were recently used for the development of hyperspectral imaging for early detection of retinal diseases where a wide range of wavelength, a small bandwidth and outstanding isolation is crucial in order to achieve an efficient illumination of the entire retina. Tunable source can be a powerful tool for reflection and transmission spectroscopy, photobiology, detector calibration, hyperspectral imaging and steady-state pump probe experiment to name only a few. History The first true broadly tunable laser was the dye laser in 1966. Hänsch introduced the first narrow-linewidth tunable laser in 1972. Dye lasers and some vibronic solid-state lasers have extremely large bandwidths, allowing tuning over a range of tens to hundreds of nanometres. Titanium-doped sapphire is the most common tunable solid-state laser, capable of laser operation from 670 nm to nm wavelength. Typically these laser systems incorporate a Lyot filter into the laser cavity, which is rotated to tune the laser. Other tuning techniques involve diffraction gratings, prisms, etalons, and combinations of these. Multiple-prism grating arrangements, in several configurations, as described by Duarte, are used in diode, dye, gas, and other tunable lasers. See also References Further reading Laser types