Q-factor cavity

Additional recommendations of value for the non-specialist to improve accuracy can be found in an early review [13], The largest source of uncertainty was attributed to differences in the microwave field strength even with identical microwave power input for different samples. The uncertainty can be reduced by using similar materials for the reference as for the sample, both contained in sample tubes of the same diameter and wall thickness, to minimize differences in the cavity Q factor between the measurements. A modern guide to quantitative ESR by the same authors is in preparation [15]. 

The cavity Q-factor can be generally defined as Q = (at where is the decay lifetime of a cavity mode [97] thus the longer is the photon lifetime inside the cavity, the higher is Q. The value Q may be influenced by various contributions and near laser threshold is give by [121] ... 

Microwave cavity Microwave field profile, cavity Q-factor, modulation field profile... 

For an RF electric field sensor, bandwidth (speed) is another important requirement. The speed of a resonator is determined by the cavity ring down time r = QX/c. As in any devices using resonating structures, a trade off between sensitivity (which increases with Q) and speed (which decreases when Q increases) has to be made. At the wavelength of 1.55 pm, Q factors of 104 and 106 translates to a sensor bandwidths of 20 GHz and 200 MHz, respectively. 

For the measurement of small absorption coefficients or refractive indices, it is often advantageous to place the probe inside the laser cavity ). The sensitivity is then increased by a factor which depends on the quality of the Q factor of the cavity and which can be very large (about 100 or more), since quite small changes in total absorption may cause large changes in laser intensity, especially if the laser is operated close above threshold. 

Emergency In vivo Tooth Dosimeter Oral Dosimeter. Tooth enamel is only material that records the accumulated radiation exposure dose in the past in a human body. An equipment for rapid dosimetry of teeth without their extraction was fabricated upon demand by Chernobyl medical doctors to judge whether immediate medical care such as spinal transplantation is necessary.97 A portable test apparatus of in vivo human tooth dosimeter consists of a resonator cavity with an aperture and a permanent magnet of Nd-B-Fe alloy (Neomax). The sensitivity is not sufficient due to the low Q factor and non-uniform magnetic field at the tooth. 

Cavities. The sample is contained in a resonant cavity, which is a structure capable of supporting a standing-wave pattern. The cavity is analogous to a tuned circuit (e.g., a parallel RLC combination) used at lower frequencies and must be matched to the klystron frequency range. A measure of the quality of the cavity is its Q or Q factor, which is defined as... 

In a Q-switched laser, the population inversion, usually produced in the same way as CW operation, builds up by making the cavity quality factor Q unfavorable for lasing. Then, when the pump energy stored in the laser medium is at the desired level, the Q is suddenly adjusted (electro- or acousto-optically) to release the pulse. This results in high peak powers. 

Where f is the frequency of the incident microwave radiation and Q is the dimensionless cavity quality factor. Thus for a typical cavity Q of 20,000 at 10 GHz the operational bandwidth is on the order of 0.5 MHz. Therefore a typical rotational spectrum that covers 7.5-18.5 GHz must be stepped in 500 kHz step sizes over that spectral range. The result is a recording device that must take 22,000 steps to record an 11 GHz spectral region leading to data acquisition times that can take upwards of 14 hours. This analysis time can be reduced to minutes if spot checks are performed by tuning the cavity only to the rotational transition of a known species, however, in tliis mode of operation, only the species of interest will be detected, i.e., molecular species with transitions outside the spectral window being monitored will not be detected. 

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