Compact Low Repetition Rate Optical Parametric Oscillators Enabled by Herriott Cells

Three-photon fluorescence microscopy exploits a tissue transparency window around 1.6−1.8 μm to enable imaging at greater depths than can be achieved using two-photon fluorescence [1], but typically requires expensive few-MHz laser sources such as optical parametric amplifiers (OPAs). Such systems are optically inefficient, requiring bulky, high-average-power pump lasers. An ultrafast optical parametric oscillator (OPO) can in theory provide the same performance with a fraction of the pump power, yet requires a long cavity length to achieve few-MHz operation in a synchronous configuration. To address this issue we present a synchronously-pumped OPO which employs an intracavity Herriott cell (HC) [2] to provide the same optical path in a compact footprint.