Architecture for high conversion efficiency optical parametric oscillators

摘要

Summary form only given. The Optical Parametric Oscillator is a convenient device for downconverting a pump wave at a frequency of /spl omega/p to two frequencies at /spl omega/s and /spl omega/i. In this contribution, since we will present with multiple parametric interactions in series, we will call signal the field which is common to all interactions whatever its frequency. The quantum efficiency (/spl eta/q) is the ratio of the number of photons converted at /spl omega/s to the initial number of pump photons. The energy conversion efficiency at /spl omega/s is related to the quantum one by the following relation: /spl eta/e=/spl eta/q/spl middot//spl lambda/p//spl lambda/s. Thus, if we assume that only the signal has a practical interest, the efficiency is limited by the wavelengths ratio /spl lambda/p//spl lambda/s shorter than 1. For example, if we intend to generate a 10 /spl mu/m wavelength radiation in an OPO pumped at 1 /spl mu/m, the energy conversion will be 10% in the best case. Recently, demonstrations have been made that it is possible to increase the quantum efficiency of an optical parametric oscillator (OPO) by using an intracavity difference frequency mixing. Presenting and analyzing a new configuration bound to overcome the quantum defect to a larger extent in the case of cw or synchronously pumped OPOs is the purpose of this contribution. Generally speaking and using the angular frequencies, one can use n cascaded parametric processes to convert photons at /spl omega/p to /spl omega/s as shown in Fig. 1 where n is the integer part of /spl omega/p//spl omega/s. The idler of the first interaction is used as a pump in the second one to generate the same signal. The idler of the second interaction is used as the pump in the third one and so on. The last interaction is at degeneracy (/spl lambda//sub s/=/spl lambda//sub i,n/=2./spl lambda//sub i,n-1/). The goal is then to obtain n signal photons for a single pump photon thanks to n cascaded processes. As different phase matching conditions are required for each interaction quasi-phase-matching offers a versatile way to get a monolithic integration of all interactions in the same crystal by engineering areas with different coherence lengths.