Coherent two-photon emission from hydrogen molecules excited by counter-propagating laser pulses

Abstract

We observed two-photon emission signal from the first vibrationally excited state of parahydrogen gas coherently excited by counter-propagating laser pulses. A single narrow-linewidth laser source has roles in the excitation of the parahydrogen molecules and the induction of the two-photon emission process. We measured dependences of the signal energy on the detuning, target gas pressure, and input pulse energies. These results are qualitatively consistent with those obtained by numerical simulations based on Maxwell-Bloch equations with one spatial dimension and one temporal dimension. This study of the two-photon emission process in the counter-propagating injection scheme is an important step toward neutrino mass spectroscopy.

QED background against atomic neutrino process with initial spatial phase

“…It turns out that the twophoton absorption process, |g + γ + γ → |e , is appropriate to prepare the initial state of the RENP with nonvanishing e|ρ a |g . We note that this scheme of coherence generation has already been realized for para-hydrogen [8]. As is described in Ref.…”

“…As a proof-of-concept of the macrocoherent amplification, the QED two-photon process in which a photon substitutes for the neutrino pair of RENP, |e → |g + γ + γ, has been studied both theoretically [4] and experimentally [5,6,7,8]. In a series of experiments, the rate enhancement of O(10 18 ) was observed.…”

Superradiant searches for dark photons in two stage atomic transitions

“…(Indeed, even continuous gigawatt lasers as powerful as we require have been demonstrated in recent years [53].) The left panel assumes experimental detuning δ = 100 MHz, as achieved in recent counter-propagating pulsed laser experiments [33]. The right panel assumes δ = 10 MHz, a linewidth that has been achieved in solid parahydrogen [51].…”

“…In the case of the first vibrationally excited state of pH 2 , the total lifetime has been observed to be T 1 ∼ 10 µs at ∼ 10 K temperatures [47][48][49], which will be appreciably longer than the decoherence time of the first pH 2 vibrational excitation at these temperatures, where this decoherence time will be of order ∼ 1 − 100 ns [50]. In more detail, the decoherence time (T 2 ) of pH 2 has been studied extensively for a variety of temperatures and densities [33,36,40,50]. In some regimes, it is accurate to use the mean interaction time of hydrogen atoms as an estimate of the decoherence time resulting from pH 2 collisions at number density n,…”

“…For pH 2 Raman linewidth measurements ∆ν dec , the decoherence times are estimated as T 2 ∼ 1 ∆ν dec . In the case of References [33,38], the decoherence time is an estimate using results from Ref. [50].…”