We demonstrate the first time a widely tunable MOPA (Master Oscillator Power Amplifier) laser system for Optical resolution photoacoustic microscopy (OR-PAM). This unique laser is capable of tuning the repetition rate (0.1- 120MHz), the wavelength (1030-1080nm), the pulse-width (100ps-5ns) and power (up to 1.1W). It is also capable of programmable dithering and synchronization with other laser systems to within ~ps jitter. To apply it to OR-PAM we take advantage of frequency doubling to convert IR light into green light. For doubling, a periodically poled magnesium doped lithium niobate (MgO:LiNbO<sub>3</sub>) crystal was chosen. Wavelength tuning was accomplished by tuning the output wavelength of the MOPA then tuning the temperature of the (MgO:LiNbO<sub>3</sub>) crystal to generate tunable visible light. Characterization of the system performance revealed a lateral resolution of ~7μm and a SNR of ~21dB when imaging 7μm carbon fibers.
High-resolution mapping of microvasculature has been applied to diverse body systems, including the retinal and choroidal vasculature, cardiac vasculature, the central nervous system, and various tumor models. Many imaging techniques have been developed to address specific research questions, and each has its own merits and drawbacks. Understanding, optimization, and proper implementation of these imaging techniques can significantly improve the data obtained along the spectrum of unique research projects to obtain diagnostic clinical information. We describe the recently developed algorithms and applications of two general classes of microvascular imaging techniques: speckle-variance and phase-variance optical coherence tomography (OCT). We compare and contrast their performance with Doppler OCT and optical microangiography. In addition, we highlight ongoing work in the development of variance-based techniques to further refine the characterization of microvascular networks.