Intracavity pumped OPO Interferometry

In this paper I present an overview of optical parametric oscillator-the basic mechanism and several advantages of it. One application of using OPO as a differential interferometer is explained in detail. The basic mechanism of OPO OPO is short for optical parametric oscillator, which consists essentially of an optical resonator and a nonlinear optical crystal. It is driven by a pump beam and generates a lower frequency under certain phase matching conditions through a (2) χ process. In the OPO the initial idler and signal frequencies are taken from background waves, which are always present. If the idler beam is provided from an outside source along with the pump beam, then the process is known as difference frequency generation (DFG). In the nonlinear optical crystal, the pump, signal and idler waves overlap. The interaction between these three waves leads to amplitude gain for signal and idler frequencies and a corresponding decrease (depletion) of the pump beam. The gain allows the resonating frequency (signal or both) to oscillate in the resonator, compensating the loss at each round-trip. The device is called singly resonant oscillator if the optical resonator serves to resonate only at signal frequency; and doubly resonant oscillator if at both. Since the loss is independent of the pump power, but the gain is dependent on pump power, oscillation occurs only when the pump power reaches a particular threshold level. In steady-state operation, the amplitude of the signal frequency is determined by the condition that this gain equals the loss. The circulating amplitude increases with increasing pump power and so does the output power. Some advantages of OPO The photon conversion efficiency of the OPO can be high, in the range of tens of percent. Typical threshold pump power is between tens of mill watts to several watts, depending on losses of the resonator, the frequencies of the interacting light, the intensity in the nonlinear material, and its nonlinearity. Output powers of several watts can be achieved. There exist both continuous-wave and pulsed OPOs. The latter are easier to build, since the high intensity lasts only for a tiny fraction of a second, which may damage the nonlinear optical material and the mirrors less than a continuous high intensity. The output frequency of an OPO is tunable. In order to change the output wave frequencies, one can change the pump frequency and the phase matching properties of the nonlinear optical crystal correspondingly. This latter is accomplished by changing its temperature or orientation or quasi-phase-matching period. For instance, with a suitable