Fabry-Perot devices

A Fabry-Perot LCTF having a spectral bandpass of better than 20 cm has been employed for Raman microscopy [25]. Although exhibiting excellent image quality, the Fabry-Perot device exhibited moderate spectral resolution, low out-of-band rejection, limited free spectral range, and a small acceptance angle. It also requires a temperature-stabilized housing to avoid thermal drift in the bandpass. 

Semiconductor laser diodes are widely used in CD players, DVDs, printers, telecommunication or laser pointers. In the structure, they are similar to LEDs but they have a resonant cavity where laser amplification takes place. A Fabry-Perot cavity is established by polishing the end facets of the junction diode (so that they act as mirrors) and also by roughening the side edges to prevent leakage of light from the sides of the device. This structure is known as a homojunction laser and is a very basic one. Contemporary laser diodes are manufactured as double heterojunction structures. 

Another recent notable technical advance has been the development of a pulsed Orotron source currently being used and tested in the 360 GHz system at Berlin. This electron-beam device (Smith Purcell free electron laser) has feedback via a high-Q Fabry-Perot cavity and thus features good frequency stability as well as pulse output powers at 360 GHz in the many tens of mW. 

There are two possible approaches towards making feasible devices. One approach is to develop device structures that need smaller coefficients to operate, e.g lossy Fabry-Perot cavities (8), the other approach is to trade-off some of the speed and low loss in current organics for larger responses, for instance by tuning into resonances. In this paper we will explore the latter route and show how this can be achieved in some materials whilst maintaining, at acceptable levels, the critical figures of merit relating the nonlinear refraction to linear loss and two photon absorption to nonlinear refraction. 

Tunable filters in the form of AOTF devices, liquid crystal tunable filter (LCTF) and also tunable cavity Fabry-Perot etalon (FPE) devices have been considered in non-moving part instrument designs for many years. Today, the AOTF and the LCTF devices are used in the NIR spectral region.9,10 Originally, designs were also proposed for mid-IR AOTF devices, but these have not become available, mainly because of fabrication issues (cost and material purity). Tunable FPE devices, which are really just variable cavity interference filters, have been developed for the telecommunications industry. While these have been primarily used in the NIR, in most cases they can be fabricated to work also in the mid-IR, the latter being only an issue of material/substrate selection. 

A device based on a porous silica substrate used as a Fabry-Perot interferometer has been reported as a sensor for organophosphorus nerve agents. The porous silica is coated with a surfactant and a copper hydrolysis catalyst. The mode of operation... 

To sweep the dye laser its beam is split and the secondary beam is driven into an acousto-optic device. The frequency-shifted beam is reflected back into the acousto-optic crystal so that one of the emerging beams is shifted twice. This beam then enters a reference Fabry-Perot cavity (indicated as FPR in Fig. 2) of very high finesse, whose length is locked to an I2 - stabilized... 

Although all laboratories that perform high-field ESR have experimented with Fabry-Perot resonators instead of fundamental mode microwave cavities, few laboratories have as yet explored quasioptical implementations of common microwave devices such as a magic T or circulator in an FIR-ESR spectrometer (see Earle and Freed, 1995 Earle et al. 1996b Smith, 1995). Part of the problem is the unfamiliar appearance of optical circuits to spectroscopists who are only familiar with... 

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