Coherent has introduced the Chameleon model optical parametric oscillator (OPO), which has been completely redesigned to provide simple access to tunable near-IR wavelengths for multiphoton excitation microscopy (MPE). When used with any model of the Chameleon family of ultrafast lasers, the new OPO delivers continuous gap-free tuning from 1,000nm to 1600nm with up to 600mW of specified output power. Moreover, tuning causes no change in beam pointing direction and thus requires no adjustments of downstream (microscope) optics.
Chameleon OPO utilises a periodically-poled crystal wherein the poling is a function of the position in the crystal, forming a fan-shaped grating. This not only yields efficient OPO wavelength conversion, but also enables the OPO to be pumped at any wavelength in the range 740nm to 880nm. The wavelength of the Chameleon oscillator and the Chameleon OPO can thus be tuned completely independently, enabling simultaneous sample excitation at two wavelengths. The tuning of both devices is controlled through a single common interface.
There are several advantages to using a tunable MPE source at longer (>1000nm) wavelengths. First it enables optimum excitation of the new m-fruit fluorophores like m-cherry. In addition, these longer wavelengths are less damaging to live tissues, and also undergo less scatter, supporting deeper images. Finally, the group velocity dispersion (GVD) of typical microscope optics is lower at these longer wavelengths, further enhancing MPE image quality.