While in the visible range single-photon detection techniques are relatively well established [6], microwave photon counters have been reported only recently [7,8,9,10,11,12,13,14]. As a matter of fact, the detection of microwave photons is extremely challenging due to their small energy. Considering frequencies in the 1GHz1mm, the equivalent energy results 4μeV
Micro Ondes Combes Pdf 17
(a) Noise detection scheme based on quantum dots (QDs). The quantum point contact (QPC), which is capacitively coupled to the double quantum dot, acts both as a source of microwave photons and as a charge sensor that probes the configuration of the DQD. (b) Scheme of the different paths that the DQD system can take after photon absorption. Γrel shows the relaxation path, where the electron returns to the ground state, emitting a phonon/photon in the process. ΓS followed by ΓD shows the charging with an additional electron through tunneling from the source contact. In the two-electron state, tunneling out of the device is permitted: this returns the system to the initial configuration. (c) Typical time trace of the detector signal. The peaks correspond to entering and leaving of the additional electron in the DQD.
Time-resolved detection of single PAT transitions requires sensitive and fast detection. QPCs would play this role but they are themselves source of microwave photons [40,42]; in a photon detector this would increase dark counts unless the detection frequency is set beyond the cut-off frequency of the QPC noise generator [40]. Moreover, QPCs typically show a response much slower than the relaxation rate of DQDs. In this respect, rf reflectometry would perform better, given that charge sensing with bandwidth up to 1.5 MHz [53] has been reported for GaAs and gate sensing with 1 μs integration time has been reported for InAs DQDs [62]. The reflectometry technique has been recently implemented also for Si/SiGe DQDs, demonstrating single-shot singlet-triplet readout with an integration time of 0.8μs [58]. For Si/SiGe DQDs, the charge relaxation time was shown to vary over four orders of magnitude as a function of detuning and interdot tunneling parameters, with a maximum value T1=45μs [74]. These results indicate that rf reflectometry can be implemented to sense the DQD at rates faster than the charge relaxation times, thus opening a way to the realization of efficient DQD based microwave photon detectors.
In this work, we present the results of a new approach of atmospheric microwave plasma torch (MPT), measuring the excitation temperature of the plasma. The new system consists of a cylindrical resonant cavity and a microwave source, a magnetron operating at a frequency of 2.45 GHz and power of 880 W, which is used to generate plasma inside a quartz tube, mounted coaxially along the cavity, with a diameter of 7 mm. The cylindrical cavity excites a dominant electric transverse mode TE111, in which surface waves transporting energy reach up to levels of 100 W/m3sr. The magnetron generator converts the input energy into plasma, in which the absorbed power is the result of the balance between the incident power and reflected power, but it depends on source losses in the cavity, the connection of the cavity, and the existence of other microwave harmonics. We use the optical emission spectroscopy to measure the excitation temperature, determined by Boltzmann plot method, based on the detection of several plasma emission lines, resulting in an excitation temperature of (3400 500)K.
At atmospheric pressure, the plasma is very near of the partial pLTE justifying the use of equilibrium equations of the Boltzmann equation for the those populations of excited states for ionization [3,4]. The justification consists of the fact that they have a high degree of ionization and the processes are dominated by electrons-ions collisions. Plasmas produced by microwaves are generally obtained from magnetron valves and have higher energies than those obtained in DC or RF plasmas, so the process is intensified [5,6].
where c is the speed of light, ωpe is the electron frequency radians per seconds, v is the momentum collision frequency in Hertz and ω is microwave frequency in radians per seconds [8].
A simplified design of a resonant cavity is illustrated in Figure 1. The system consists of a cylindrical stainless-steel tube with an internal diameter of 100 mm and length of 210 mm. The cavity is set to house a magnetron, the same used in conventional microwave ovens, in the center of the cylinder. Discharge forms in a quartz tube with an internal diameter of 7 mm and length of 250 mm. The quartz tube is aligned with the magnetron to allow plasma formation throughout its length. The experiment was carried out to study the emission spectrum of argon in a resonant cavity, and plasma was generated inside a quartz tube by microwaves (Figure 1). For the formation of the plasma at the exit of the quartz tube, an argon flow of 1 L/min is required.
The result obtained in this study, an excitation temperature of about 3400 K, is similar to those of plasmas generated in the same conditions, i.e., atmospheric pressure, and same source of energy, (microwaves); in this case, it was not necessary to use a waveguide for its formation. The critical point in the construction of the resonant cavity is the distance between the side covers, which, being movable, allows its precise adjustment in the determination of the exact length in order to activate the plasma, as a variation of tenths of millimeters enables the adjustment of resonance. Another relevant point is the simplicity of the construction of the chamber, which consists of a metal cylinder with movable covers. Another important point in the formation of the plasma torch is the argon flux, at about 1 L/min. The quartz tube, responsible for conducting the gas, can also be combined in different diameters because, in the side cover, there is a pre-support responsible for fixing the tube and is adjustable for different diameters, allowing for other applications and studies. Again, with respect to the excitation temperature, the experiment proves effective in the yield of energy, as the magnetron of 800 W allows high temperatures. 2ff7e9595c
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