157 research outputs found
Radiative lifetimes of GdI and GdII
Natural radiative lifetimes of 25 even-parity levels in Gd i (4f(7) 5d(2) 6p, 4f(7)5d6s6p and 4f(8)5d6s configurations) and 13 even-parity levels in Gd it (4f(7)5d6p and 4f(7)6s6p configurations) have been measured using the time-resolved laser-induced fluorescence technique in a laser-induced gadolinium plasma. The Gd I and Gd it levels range in energy from 26 866 to 36 395 cm(-1), and 25 960 to 42 746 cm(-1), respectively. In the measurements, stimulated Brillouin scattering techniques were employed to produce I ns laser pulses to enable accurate measurements of short-lived states. The uncertainty of the radiative lifetimes is, with a few exceptions. about +/-5%
Lifetime measurements in neutral and singly ionized vanadium
Radiative lifetimes of ten odd-parity levels of V I belonging to the 3d(3)4s4p and 3d(4)4p configurations and of 11 odd-parity levels of V II belonging to the 3d(3)4p configuration are reported. The lifetimes were measured with use of single-step excitation and time-resolved fluorescence spectroscopy. The neutral and singly ionized vanadium atoms were produced in a laser-induced vanadium plasma. (c) 2006 Optical Society of America
Impulsive rotational Raman scattering of N2 by a remote "air laser" in femtosecond laser filament
We report on experimental realization of impulsive rotational Raman
scattering from neutral nitrogen molecules in a femtosecond laser filament
using an intense self-induced white-light seeding "air laser" generated during
the filamentation of an 800 nm Ti: Sapphire laser in nitrogen gas. The
impulsive rotational Raman fingerprint signals are observed with a maximum
conversion efficiency of ~0.8%. Our observation provides a promising way of
remote identification and location of chemical species in atmosphere by
rotational Raman scattering of molecules.Comment: 4 pages, 4 figure
High-brightness switchable multi-wavelength remote laser in air
Remote laser in air based on amplified spontaneous emission (ASE) has
produced rather well-collimated coherent beams in both backward and forward
propagation directions, opening up possibilities for new remote sensing
approaches. The remote ASE-based lasers were shown to enable operation either
at ~391 and 337 nm using molecular nitrogen or at ~845 nm using molecular
oxygen as gain medium, depending on the employed pump lasers. To date, a
multi-wavelength laser in air that allows for dynamically switching the
operating wavelength has not yet been achieved, although this type of laser is
certainly of high importance for detecting multiple hazard gases. In this
Letter, we demonstrate, for the first time to our knowledge, a harmonic-seeded
switchable multi-wavelength laser in air driven by intense mid-infrared
femtosecond laser pulses. Furthermore, population inversion in the
multi-wavelength remote laser occurs at an ultrafast time-scale (i.e., less
than ~200 fs) owing to direct formation of excited molecular nitrogen ions by
strong-field ionization of inner-valence electrons, which is fundamentally
different from the previously reported pumping mechanisms based either on
electron recombination of ionized molecular nitrogen or on resonant two-photon
excitation of atomic oxygen fragments resulting from resonant two-photon
dissociation of molecular oxygen. The bright multi-wavelength laser in air
opens the perspective for remote detection of multiple pollutants based on
nonlinear spectroscopy.Comment: 18 pages, 5 figure
Lifetimes along perturbed Rydberg series in neutral thallium
Radiative lifetimes of 15 Tl I levels belonging to the 6s(2)ns(2)S(1/2) (n = 7-14) and 6s(2)nd(2)D(3/2) Rydberg series (n = 6-12) have been measured using a time-resolved laser-induced fluorescence technique. All the measured levels have been excited from the ground state 6s(2)6p(2)P(1/2)(0) (odd parity) with a single-step excitation process. The general perturbation of the ns series by the 6s6p(2) configuration and the corresponding modification of the lifetimes are adequately reproduced by a theoretical model including core-polarization effects and combined with a least-squares fit to the observed energy levels. The general behaviour of the lifetime values for the 6s(2)np odd levels along the Rydberg series is also well reproduced. The use of the multiconfiguration quantum defect theory has allowed us to obtain lifetime values along the 6s(2)ns(2)S(1/2) series up to levels with n = 31
Remote creation of strong and coherent emissions in air with two-color ultrafast laser pulses
We experimentally demonstrate generation of strong narrow-bandwidth emissions
with excellent coherent properties at ~391 nm and ~428 nm from molecular ions
of nitrogen inside a femtosecond filament in air by an orthogonally polarized
two-color driver field (i. e., 800 nm laser pulse and its second harmonic). The
durations of the coherent emissions at 391 nm and 428 nm are measured to be
~2.4 ps and ~7.8 ps respectively, both of which are much longer than the
duration of the pump and its second harmonic pulses. Furthermore, the measured
temporal decay characteristics of the excited molecular systems suggest an
"instantaneous" population inversion mechanism that may be achieved in
molecular nitrogen ions at an ultrafast time scale comparable to the 800 nm
pump pulse.Comment: 19 pages, 4 figure
Sub-10-fs population inversion in N2+ in air lasing through multiple state coupling
Laser filamentation generated when intense laser pulses propagate in air has been an attractive phenomenon having a variety of potential applications such as detection and spectroscopy of gases at far distant places. It was discovered recently that the filamentation in air induces ‘lasing’, showing that electronically excited N2+ is population-inverted, exhibiting marked contrast to the common understanding that molecular ions generated by intense laser fields are prepared mostly in their electronic ground states. Here, to clarify the mechanism of the population inversion, we adopt few-cycle laser pulses, and experimentally demonstrate that the lasing at 391 nm occurs instantaneously after N2+ is produced. Numerical simulations clarify that the population inversion is realized by the post-ionization couplings among the lowest three electronic states of N2+. Our results shed light on the controversy over the mechanism of the air lasing, and show that this post-ionization coupling can be a general mechanism of the atmospheric lasing.UTokyo Research掲載「レーザーが空気中で増幅される機構を解明」 URI: http://www.u-tokyo.ac.jp/ja/utokyo-research/research-news/mechanism-of-air-lasing.htmlUTokyo Research "Mechanism of air lasing" URI: http://www.u-tokyo.ac.jp/en/utokyo-research/research-news/mechanism-of-air-lasing.htm
Hyperfine structure and homogeneous broadening in Pr3+: KY(WO4)(2)
As part of a search for suitable materials for coherent quantum operations, relaxation times and hyperfine structure of the D-1(2)(1)-H-3(4)(1) transition in Pr3+:KY(WO4)(2) (0.29 at. %) at 4 K have been obtained using photon-echo and spectral hole burning techniques. The homogeneous linewidth and the effect of excitation-induced dephasing were measured using two-pulse photon-echo techniques. Linewidths of 23.4+/-1.0 and 17.6+/-0.9 kHz were obtained in the absence and presence of an external magnetic field of about 9 mT. The radiative lifetime (T-1) of the D-1(2) state was measured to be 43+/-2 mus using time-resolved laser-induced fluorescence and three-pulse photon-echo measurements. The transmission hole spectra were measured and directly yielded the quadrupole level splitting in the D-1(2) (3.77+/-0.03 and 4.58+/-0.04 MHz) and H-3(4) (17.1+/-0.1 and 33.2+/-0.3 MHz) states. The spectral hole lifetime due to population redistribution between the ground-state nuclear levels was also determined to be 70+/-10 ms. A strong dipole-dipole interaction observed in this crystal opens for potential applications in quantum computing schemes for performing quantum logic operations, but the short dephasing time makes it less useful in data storage applications
Self-induced white-light seeding laser in a femtosecond laser filament
We report, for what we believe to be the first time, on the generation of
remote self-seeding laser amplification by using only one 800 nm Ti:Sapphire
femtosecond laser pulse. The laser pulse (~ 40 fs) is first used to generate a
filament either in pure nitrogen or in ambient air in which population
inversion between ground and excited states of nitrogen molecular ions is
realized. Self-induced white light inside the filament is then serving as the
seed to be amplified. The self-induced narrow-band laser at 428 nm has a pulse
duration of ~2.6 ps with perfect linear polarization property. This finding
opens new possibilities for remote detection in the atmosphere.Comment: 18 pages, 5 figure
Harmonic-seeded remote laser emissions in N2-Ar, N2-Xe and N2-Ne mixtures: a comparative study
We report on the investigation on harmonic-seeded remote laser emissions at
391 nm wavelength from strong-field ionized nitrogen molecules in three
different gas mixtures, i.e., N2-Ar, N2-Xe and N2-Ne. We observed a decrease in
the remote laser intensity in the N2-Xe mixture because of the decreased
clamped intensity in the filament; whereas in the N2-Ne mixture, the remote
laser intensity slightly increases because of the increased clamped intensity
within the filament. Remarkably, although the clamped intensity in the filament
remains nearly unchanged in the N2-Ar mixture because of the similar ionization
potentials of N2 and Ar, a significant enhancement of the lasing emission is
realized in the N2-Ar mixture. The enhancement is attributed to the stronger
third harmonic seed, and longer gain medium due to the extended filament.Comment: 10 pages, 5 figure
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