arXiv subjects

Noboru Sasao

Publications and source records attributed to Noboru Sasao.

29 records · Page 2Linked to original sources

arXiv2018

Geometry-dependent spectra and coherent-transient measurement of nearly degenerate four-wave mixing using two-photon resonance

We study nearly degenerate four-wave mixing using a two-photon-allowed vibrational transition of parahydrogen. A signal photon is generated by a trigger photon and coherence among parahydrogen, which is prepared by two counterpropagating pump pulses. The dependence of the signal pulse energy on the trigger frequency are investigated. The measured spectra vary depending on the geometry. They shift depending on the direction of the signal pulse and on the small angle formed by the counterpropagating pump pulses. Furthermore, the dependence of signal pulse energy on the incident time of the trigger pulse is investigated. The measured signal pulse energy is high if the trigger pulse is slightly delayed with respect to the pump pulses. We demonstrate that these geometry-dependent spectra and coherent-transient response can be explained by using simple models.

physics.atom-ph↗

arXiv2017

Effects of initial spatial phase in radiative neutrino pair emission

We study radiative neutrino pair emission in deexcitation process of atoms taking into account coherence effect in a macroscopic target system. In the course of preparing the coherent initial state to enhance the rate, a spatial phase factor is imprinted in the macroscopic target. It is shown that this initial spatial phase changes the kinematics of the radiative neutrino pair emission. We investigate effects of the initial spatial phase in the photon spectrum of the process. It turns out that the initial spatial phase provides us significant improvements in exploring neutrino physics such as the Dirac-Majorana distinction and the cosmic neutrino background.

hep-ph↗

arXiv2017

Towards Background-free RENP using a Photonic Crystal Waveguide

We study how to suppress multiphoton emission background in QED against radiative emission of neutrino pair (RENP) from atoms. We purse the possibility of background suppression using the photonic band structure of periodic dielectric media, called photonic crystals. The modification of photon emission rate in photonic crystal waveguides is quantitatively examined to clarify the condition of background-free RENP.

physics.optics↗

arXiv2017

Injection seeded tunable mid-infrared pulses by difference frequency mixing

We report on the generation of nanosecond mid-infrared pulses having frequency tunability, a narrow linewidth, and a high pulse energy. These pulses are obtained by frequency mixing between injection-seeded near-infrared pulses in potassium titanyl arsenate crystals. A continuous-wave external cavity laser diode or a Ti:sapphire ring laser is used as a tunable seeding source for the near-infrared pulses. The typical energy of the generated mid-infrared pulses is in the range of 0.4-1 mJ/pulse. The tuning wavelength ranges from 3142 to 4806 nm. A narrow linewidth of 1.4 GHz and good frequency reproducibility of the mid-infrared pulses are confirmed by observing a rovibrational absorption line of gaseous carbon monoxide at 4587 nm.

physics.optics↗

arXiv2016

Vibrational two-photon emission from coherently excited solid parahydrogen

We report observation of two-photon emission from coherently excited vibrational state of solid parahydrogen, known as one of quantum solids. The coherent state between the ground and the excited states is prepared by stimulated Raman scattering using two visible laser pulses. The two-photon emission is triggered by another mid-infrared laser pulse. The observed two-photon emission persists even when the trigger pulse is injected long after the excitation. The observed phenomenon is due to a long decoherence time of the vibrational states of solid parahydrogen, which is attributed to special nature as quantum solid. Dependence of the decoherence on target temperature and residual orthohydrogen concentration are studied along with its time evolution. It is found that the emission intensity increases even after the excitation pulses pass through the target completely. The coherence development is highly suppressed at high target temperature and high residual orthohydrogen concentration. Effects of target annealing and laser-induced damage on the target are also observed.

physics.chem-ph↗

arXiv2015

Externally triggered coherent two-photon emission from hydrogen molecules

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 two-photon 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.

physics.atom-ph↗

arXiv2014

Simultaneous measurements of super-radiance at multiple wavelengths from helium excited states: (I) Experiment

In this paper, we report the results of measurements of the intensities and delays of super-radiance decays from excited helium atoms at multiple wavelengths. The experiment was performed using extreme ultraviolet radiation produced by the free electron laser at the SPring-8 Compact SASE Source test accelerator facility as an excitation source. We observed super-radiant transitions on the $1s3p \to 1s2s$ ($λ=$502 nm), $1s3d \to 1s2p$ ($λ=$668 nm), and $1s3s \to 1s2p$ ($λ=$728 nm) transitions. The pulse energy of each transition and its delay time were measured as a function of the target helium gas density. Several interesting features of the data, some of which appear to contradict with the predictions of the simple two-level super-radiance theory, are pointed out.

physics.atom-ph↗

arXiv2014

Observation of coherent two-photon emission from the first vibrationally-excited state of hydrogen molecules

In this paper, we describe an experiment which was conducted to explore the macro-coherent amplification mechanism using a two-photon emission process from the first vibrationally-excited state of para-hydrogen molecule. Large coherence in the initial state was prepared by the adiabatic Raman population transfer method, and the lowest Stokes sideband was used as a trigger field. We observed the coherent two-photon emission consistent with the expectation of the paired super-radiance master equation.

physics.atom-ph↗

arXiv2013

I$_{2}$ molecule for neutrino mass spectroscopy: ab initio calculation of spectral rate

It has recently been argued that atoms and molecules may become good targets of determining neutrino parameters still undetermined, if atomic/molecular process is enhanced by a new kind of coherence. We compute photon energy spectrum rate arising from coherent radiative neutrino pair emission processes of metastable excited states of I$_2$ and its iso-valent molecules, $|Av \rangle \rightarrow |Xv' \rangle + γ+ ν_iν_j$ and $|A'v \rangle \rightarrow |Xv' \rangle + γ+ ν_iν_j$ with $γ$ an IR photon and $ν_{i(j)}$ $i(j)-$th neutrino mass eigenstates, and show how fundamental neutrino parameters may be determined. Energies of electronically excited states of I$_2$, including the effect of spin-orbit couplings were calculated by the multiconfigurational second order perturbation (CASPT2) method. Summation over many vibrational levels of intermediate states is fully incorporated. Unlike atomic candidate of a much larger energy difference such as Xe, I$_2$ transitions from a vibrational level $A(v=0)$ to $X(v' = 24)$ give an opportunity of determination of the mass type (Majorana vs Dirac distinction) and determination of Majorana CPV (charge-conjugation parity violating) phases, although the rate is much smaller.

hep-ph↗

arXiv2012

Neutrino Spectroscopy with Atoms and Molecules

We give a comprehensive account of our proposed experimental method of using atoms or molecules in order to measure parameters of neutrinos still undetermined; the absolute mass scale, the mass hierarchy pattern (normal or inverted), the neutrino mass type (Majorana or Dirac), and the CP violating phases including Majorana phases. There are advantages of atomic targets, due to the closeness of available atomic energies to anticipated neutrino masses, over nuclear target experiments. Disadvantage of using atomic targets, the smallness of rates, is overcome by the macro-coherent amplification mechanism. The atomic or molecular process we use is a cooperative deexcitation of a collective body of atoms in a metastable level |e> emitting a neutrino pair and a photon; |e> -> |g> + gamma + nu_i nu_j where nu_i's are neutrino mass eigenstates. The macro-coherence is developed by trigger laser irradiation. We discuss aspects of the macro-coherence development by setting up the master equation for the target quantum state and propagating electric field. With a choice of heavy target atom or molecule such as Xe or I_2 that has a large M1 x E1 matrix element between |e> and |g>, we show that one can determine three neutrino masses along with the mass hierarchy pattern by measuring the photon spectral shape. If one uses a target of available energy of a fraction of 1 eV, Majorana CP phases may be determined. Our master equation, when applied to E1 x E1 transition such as pH_2 vibrational transition Xv=1 -> 0, can describe explosive PSR events in which most of the energy stored in |e> is released within a few nanoseconds. The present paper is intended to be self-contained explaining some details related theoretical works in the past, and further reports new simulations and our ongoing experimental efforts of the project to realize the neutrino mass spectroscopy using atoms/molecules.

hep-ph↗

arXiv1999

Development of a Laser Wire Beam Profile Monitor (I)

A conceptual design work and a basic experimental study of a new beam profile monitor have been performed. The monitor will be used to measure emittance of an electron beam in the ATF damping ring at KEK, in which the transverse beam size of about 10 micron is expected. It utilizes a CW laser and an optical cavity, instead of a material wire, to minimize interference with an electron beam. A laser beam with a very thin waist is realized by employing the cavity of nearly concentric mirror configuration while the intensity is amplified by adjusting the cavity length to a Fabry-Perot resonance condition. We built a test cavity to establish a method to measure important parameters such as a laser beam waist and a power enhancement factor. Three independent methods were examined for the measurement of the beam waist. It was found that the cavity realized the beam waist of 20 micron with the power enhancement factor of 50.

hep-ex↗