"Stark-state resonances induced by low-frequency elliptically polarized fields" https://iopscience.iop.org/article/10.1088/0953-4075/30/18/007
"We analyze the effect of a low-frequency elliptically polarized electric field on an excited hydrogen atom using classical dynamics. It is shown that at particular frequencies the ionization probability is a non-monotonic function of the field strength and that at these frequencies the classical ionization probabilities agree well with those of experiment. We show that this unusual behaviour is produced by resonance between Stark states and the driving field near the circularly polarized limit."
Microwave radiation is non-ionizing radiation. However, under certain conditions a microwave frequency can induce ionization. Can you elaborate and specifically mention which frequency is this?
Enhanced ionization of hydrogen can occur, if a static electric field is combined parallelly with a microwave field [1]. The static electric field shifts the energy level of the electron (Stark shift) to specific new levels. Resonances may be established between these and the microwave field thereby leading to ionization. A tunneling mechanism may be involved which allows the electron to overcome an energetic barrier. Transitions may take place simultaneously at several frequencies due to resonances [2].
The ionization may be dependent on the strength of the static field. It can occur on a narrow range of static field strengths and can be sensitive to small changes of strength [6]. The polarization of the microwave may also significantly influence the ionization. Notable results are reported for circularly and elliptically polarized microwaves [1] and a specific interest has been demonstrated for low-frequency elliptically polarized microwaves which show enhanced hydrogen ionization at specific frequencies [3].
What is the microwave frequency that ionizes hydrogen? The scientists report results that they obtained using microwaves of 8.105 GHz ([1] and cited therein Galvez et al 2005) and 3.5539 GHz (Schlultz 2003 referenced by [1]). Also, 9.904 GHz is used by [3] and cited therein Bellermann et al (1996, 1997).
The lowest frequency of the above is a microwave which is just over the UHF limit of 3 GHz. The 3 to 30 GHz band represents the Super High Frequency (SHF) range which has the notable feature of being used for most RADAR transmitters.
Initial experiments in this scientific area were studying the ionization of hydrogen either under the effect of the static electric field or under the effect of the microwave field [4]. In the last case, indicative frequencies of 9.92 GHz and 36.02 GHz are cited [4]. Also, it is mentioned that typical experimental conditions in these experiments are represented by the use of 10 GHz [3].
Note: Scientists may mention that they use a microwave cavity of the specified frequency.
References
[1] Richards, D. (2005). The effect of parallel static and microwave electric fields on excited hydrogen atoms. New Journal of Physics, 7, 138. https://doi.org/10.1088/1367-2630/7/1/138 (pdf available)
[2] Oks, E., & Uzer, T. (2000). Multifrequency resonance transitions in the ionization of hydrogen by a single-frequency microwave field. Journal of Physics B, 33(11), 1985–1995. https://doi.org/10.1088/0953-4075/33/11/301 (pdf on deepdyve - free 14 day trial)
[3] Richards, D. (1997). Stark-state resonances induced by low-frequency elliptically polarized fields. Journal of Physics B: 30(18), 4019–4047. https://doi.org/10.1088/0953-4075/30/18/007 (pdf on deepdyve - free 14 day trial)
[4] Heppenheimer T.A. NSF Periodical “Mosaic” Vol. 20, No 2, 1989 p.2 https://bit.ly/3nlZUD4
[5] Shepelyansky, D. (2012). Microwave ionization of hydrogen atoms - Scholarpedia. http://www.scholarpedia.org/article/Microwave_ionization_of_hydrogen_atoms
[6] Yiwu, D., Menya, Y., Weike, A., & Chunshan, H. (1999). A One-Dimensional Model of Hydrogen Molecular Ion. Communications in Theoretical Physics, 31(1), 27–32. https://doi.org/10.1088/0253-6102/31/1/27