Fabry-Perot resonator resonance frequency

Experimental Techniques. A block diagram of the experimental set-up used for saturated absorption experiments is shown in Figure 1. The argon laser is a commercial 4W tube in a home made cavity. This cavity is made of three Invar rods, decoupled from the tube in order to avoid vibrations. Line selection is made with a prism, and single frequency operation is obtained with a Michel son interferometer. The laser can be frequency locked to a stable Fabry-Perot resonator with a double servo-loop acting on a fast PZT for line narrowing and on a galvo-plate for wide tuna-bility. This results in a linewidth of less than 10 KHz and a continuous tunability of 6 GHz. 

Earlier work by Lee and White was repeated by Fehse et al using a double resonance crossed Fabry-Perot spectrometer with frequency modulation of the probe source. Both worked in the 26-40 GHz region for the probe frequency, with 15 GHz and 23 GHz pump radiation respectively. The work was not reported in any great depth but served to illustrate that the technique was viable according to both sets of workers, if less sensitive than conventional Stark spectrometry. 

Two screening studies have been done on the dielectric properties of an SiOC-Nextel 312 BN composites. In the first study in 1992 by Lockheed Missiles, a frequency range of 8 to 12 GHz was used and the properties were measured by either a Horn-Lens dielectrometer or a Fabry-Perot resonator system. All measurements were taken at room temperature. The composites were prepared from eight plies of AF-14 plain weave fabric. Four infiltration cycles were used for densification. The total porosity of the composites was about 11 %. The data generated for the Nextel 312 system are shown in Figure 20. Note that as an additional processing variable, two test specimens were heated in air (at 450°C and at 750°C) to remove any residual carbon. 

In continuous-wave electron spin resonance, extended multifrequency capabilities from 0.3 to over 100 GHz have been developed based on loop-gap and other types of resonators. The lower frequencies seem particularly useful for some biological applications. Very high frequency spectrometers have also been developed up to 700 GHz, with commercial instrumentation available at 95 GHz. The higher frequencies are based on Fabry-Perot resonators and give superior g-anisotropy resolution, suppression of second-order effects, and better sensitivity for small samples. 

Laser spectroscopy of the 1S-2S transition has been performed by Mills and coworkers at Bell Laboratories (Chu, Mills and Hall, 1984 Fee et al, 1993a, b) following the first excitation of this transition by Chu and Mills (1982). Apart from various technicalities, the main difference between the 1984 and 1993 measurements was that in the latter a pulse created from a tuned 486 nm continuous-wave laser with a Fabry-Perot power build-up cavity, was used to excite the transition by two-photon Doppler-free absorption, followed by photoionization from the 2S level using an intense pulsed YAG laser doubled to 532 nm. Chu, Mills and Hall (1984), however, employed an intense pulsed 486 nm laser to photoionize the positronium directly by three-photon absorption from the ground state in tuning through the resonance. For reasons outlined by Fee et al. (1993b), it was hoped that the use of a continuous-wave laser to excite the transition would lead to a more accurate determination of the frequency interval than the value 1233 607 218.9 10.7 MHz obtained in the pulsed 486 nm laser experiment (after correction by Danzmann, Fee and Chu, 1989, and adjustment consequent on a recalibration of the Te2 reference line by McIntyre and Hansch, 1986). 

Moreover, in recent years broad band lasers have appeared which lack any frequency modal structure, at the same time retaining such common properties of lasers as directivity and spatial coherence of the light beam at sufficiently high spectral power density. The advantages of such a laser consist of fairly well defined statistical properties and a low noise level. In particular, the authors of [245] report on a tunable modeless direct current laser with a generation contour width of 12 GHz, and with a spectral power density of 50 /xW/MHz. The constructive interference which produces mode structure in a Fabry-Perot-type resonator is eliminated by phase shift, introduced by an acoustic modulator inserted into the resonator. 

The frequencies at the red and infrared radiations inside the etalon Fabry-Perot cavity are determined by the resonant condition /10/... 

If we have a two-level sample we expect to see a series of resonances separated by half the inverse of the repetition rate of the laser as the carrier frequency is scanned. If a second transition is within the bandwidth of the laser then this too will give rise to a series of resonances. The resulting spectrum is rather like that obtained from a Fabry-Perot interferometer with overlapping orders. However, in the mode-locked case the modes are precisely equally spaced in frequency. 

The first stage was the production of a pulsed free-jet molecular beam of helium containing 20% CO, which was then crossed with an electron beam to produce ionisation. The ions were produced close enough to the beam nozzle for cooling to occur downstream. Some 4 cm from the nozzle the beam entered a confocal Fabry-Perot cavity where it was exposed to millimetre wave radiation close to 120 GHz in frequency. Following microwave excitation, when on resonance, the beam was probed with a Nd YAG pumped dye laser beam with the frequency chosen to drive rovibronic components of the A 2 U-X 2 + band system. Figure 11.54 shows two recordings of a spin component of the lowest rotational transition the line shown in (a) is... 

Despite all of the above-mentioned limitations in accuracy of optical interferometry, it is still widely used in the determination of the wave-numbers of atomic transitions, since optical frequency metrology (synthesis chains, optical frequency combs, etc, 4) does not yet have the wide spectral coverage provided by the broad-band interferometers. As an example, a recent absolute wave-number determination of the Cs D2 resonance line at 852 nm is with a Fabry-Perot interferometer, saturated absorption and a grating-eavity semiconductor laser [76]. These results are of interest to various Cs atomic fountain measurements and lead to better determinations of fundamental constants, such as h/mp and a, [77] as well as of the acceleration due to gravity, g [78,79]. 

This glitch is caused by interaction between the cavity and the sample resonance profiles. It may be converted into an apparent frequency shift of the cavity resonance that is directly related to the absolute absorption coefficient. The linewidth can be determined fi-om the distance between the peaks of the glitch. This phenomenon became even more marked with the Mark II confocal Fabry-Perot cavity (Section 5.3), when it could be observed as a glitch in the correction voltage applied by the servo amplifier to the piezoelectric actuator of the moveable cavity mirror. Figure 4.7 shows a spectrum for the water line obtained in this manner. 

Another approach to MMW spectrometers is based on the Orotron This device, called after the Russian words for an open resonator and a reflection grating, was a semiconfocal Fabry-Perot cavity (Figure 5.1) with the plane mirror having a reflection grating ruled upon it. The cavity, with 0 lO, produced a spectral bandwidth without frequency locking 10-15 kHz and output power was 3-10 mW over 90-150 GHz. 

We will describe briefly the principles of the Fabry-Perot cavity, the principles of the pulsed molecular nozzle and subsequent expansion into a vacuum, the simultaneous polarization of the gas by a microwave pulse, and finally the subsequent coherent emission at the appropriate resonance frequencies. Several examples of the operation of this apparatus will be given, followed by a thorough description of the apparatus. 

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