Optical ring cavity

The Chapter is organized as follows. First the theoretical calculations with A -type three-level atoms in the optical ring cavity are described. The EIT-enhanced linear and nonlinear dispersions are calculated, and their effects to the cavity linewidth are discussed in different parametric regions. Second, various experimental observations are presented to demonstrate those interesting effects on cavity linewidth narrowing and broadening, as well as WLC. The last part serves as the summary with some discussions. 

For an optical ring cavity of length L with an intracavity medium, as shown in Fig. 1(a), the transmitted intensity h is given by the well-known Airy function ... 

Cronin-Golomb, M., B. Fisher, J. O. White, and A. Yariv. 1983. Passive phase conjugate mirror based on self-induced oscillation in an optical ring cavity. Appl. Phys. Lett. 42 919. 

It is well known that by inserting an optical amplifier obtained by population inversion in an optical cavity, one can realize sources of coherent radiations, namely lasers. One can operate in the same way with parametric amphfication as shown on Fig. 1. A nonlinear crystal illuminated by an input pump is inserted in an optical cavity. This cavity is represented for convenience as a ring cavity but consists usually of a linear cavity. An important difference with the laser is that there are three different fields, insfead of one, which are presenf in the amplifying medium, all these fields being able to be recycled by the cavity mirrors. One obtain thus different types of "Optical Parametric Oscillators" or OPOs. 

Fig. 5.1 Four mirror ring cavity model. Left, microcavity and tapered fiber in contact. Light can couple from the fiber into the resonator and back into the fiber. Right, the four mirror ring cavity equivalent. The top mirror is partially transmitting all others have 100% reflectivity. Reprinted from Ref. 3 with permission. 2008 Optical Society of America...

The first equation is realized at the LKB while the second one is carried out at the LPTF. A first titanium-sapphire laser excites the hydrogen transition. A laser diode (power of 50 mW) is injected by the LD/Rb standard and frequency doubled in a LiBsOs (LBO) crystal placed in a ring cavity. The generated UV beam is frequency compared to the frequency sum (made also in a LBO crystal) of the 750 and 809 nm radiations produced by a second titanium-sapphire laser and a laser diode. A part of the 809 nm source is sent via one fiber to the LPTF. There, a 809 nm local laser diode is phase locked to the one at LKB. A frequency sum of this 809 nm laser diode and of an intermediate CO2 laser in an AgGaS2 crystal produces a wave at 750 nm. This wave is used to phase lock, with a frequency shift S, a laser diode at 750 nm which is sent back to the LKB by the second optical fiber. This 750 nm laser diode is frequency shifted by lyfCOo) + S with respect to the one at 809 nm. In such a way, the two equations are simultaneously satisfied and all the frequency countings are performed in the LKB. Finally, the residual difference between the two titanium-sapphire lasers is measured with a fast photodiode or a Schottky diode. 

Without absorbing species between the mirrors (Figure 4a), the ring down time of the optically empty cavity is given by (eq.2) ... 

Instead of this type of linear resonator, the majority of modem dye lasers are setup with unidirectional ring cavities, as in the example shown in Figure 4.11. Despite their much greater complexity, because of the many additional optical components required for its implementation, they have distinct advantages (specifically related to reliable single-mode tuning). 

O Keefe A and Deacon DAG 1988 Cavity ring-down optical spectrometer for absorption-measurements using pulsed laser sources Rev. Sol. Instrum. 59 2544-51... 

O Keefe, A., and D. A. G. Deacon, Cavity Ring-Down Optical Spectrometer for Absorption Measurements Using Pulsed Laser Sources, Rev. Sci. Instrum, 59, 2544-2551 (1988). 

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