Externally triggered coherent two-photon emission from hydrogen molecules

Abstract

We report coherent enhancement of two-photon emission from the excited vibrational state of molecular hydrogen triggered by irradiating mid-infrared pulses externally. We previously observed the two-photon emission triggered by the internally generated fourth Stokes photons.By injecting independent mid-infrared pulses externally, it is possible to control experimental parameters and investigate the mechanism in more detail. In this article, we describe the twophoton emission using the external trigger pulses. Its spectrum and dependence on the energy and timing of the trigger pulse are presented along with numerical simulations based on the Maxwell-Bloch equations. The measured number of emitted photons is 6×10 11 photons/pulse and the resulting enhancement factor from the spontaneous emission is more than 10 18 . This value is three orders of magnitude higher than that of the previous experiment. External control of emission process is expected to be essential for observation of weaker process of radiative emission of neutrino pair.

Frequency dependence of coherently amplified two-photon emission from hydrogen molecules

“…Each data point represents a pulse energy averaged over 200 pulses. The measured dependence for each wavelength is represented by a linear function; this was behavior that we have observed previously [15]. It is consistent with a simulation using the Maxwell-Bloch equations in the case of low trigger energy.…”

“…Recently, we succeeded in coherently amplifying the TPE process from the first vibrationally excited state of the electronic ground state (X 1 + g ) of parahydrogen molecules (p-H 2 ) [14,15], the energy diagram of which is shown in Fig. 1.…”

“…In our previous paper [15], we fixed the frequency of the trigger pulse at roughly half the energy difference of the vibrational levels. In the present paper, in contrast, we vary the frequency of the TPE signal by changing the frequency of the trigger pulses.…”

“…The present paper reports measurements of the frequency dependence of coherently amplified TPE over the wavelength range of 5.048-10.21 μm, and also presents an optical generation procedure that differs from ordinary optical parametric processes in nonlinear crystals. Figure 2 shows the experimental setup, which is a modification of one described previously [15]. In the present experiment, the frequency of the trigger field can be tuned.…”

Propagation studies for the construction of atomic macro-coherence in dense media as a tool to investigate neutrino physics

“…The extremely small cross section of the process makes the photon analysis extremely challenging, being necessary lives times of the order of days to years [10]. However on one hand we can increase the signal yield by previously preparing the target in a maximum superposition of states -similarly to the process of superradiance suggested by Dicke in 1954 [11]-where the signal yield rather than scaling with N, which is clearly insufficient, scales with N methods and techniques that provide us with an exquisite control over the amplification mechanisms in previously prepared macroscopic targets [13][14][15]. According to this, it seems mandatory to develop robust laser-matter interaction techniques capable of inducing maximum coherence in macroscopic targets.…”