A robust and compact blue optical frequency reference within blue region was designed. A 40-mW tellurium-stabilized single-frequency blue diode laser in external cavity was designed with an absorption spectroscopy method based on tellurium molecular transitions. Furthermore, the uncertainty of the frequency stabilization can be pushed to 2 x 10(-9) at a 10-s integration time. In addition, the correspondence frequency instability was 1.3 MHz when the laser wavelength was 445.75 nm. This study indicates that high-stability frequency reference within the blue region can be achieved with an external cavity diode laser as opposed to the diode-pumped frequency-doubled solid-state laser.

We designed a single-frequency green laser system that can deliver a 60-mW frequency-tunable single-longitudinal-mode laser beam, having a 6.5 MHz linewidth at around 519 nm. An external cavity diode laser can provide a wavelength-tunable single frequency laser beam, but its output power is limited. Therefore, an injection-locked laser was designed with a Fabry-Perot type green InGaN laser diode in an external Littrow-type cavity as the master laser and another laser diode of the same model as the slave laser. Injection locking can effectively enhance the output power and narrow the linewidth of the master laser. We found that the injection locking occurred at longitudinal mode matching between the master laser and slave laser diodes, which is located at a specific frequency for a periodical applied current. The side peaks of the injection locking due to the transverse mode mismatching were recorded and analyzed.

We theoretically investigate the four-wave mixing (FWM) characteristics in a Xi-V type atomic system. The generated FWM is obtained by utilizing the density matrix formalism and solving the master equation. Interesting discrimination in the number of emerged peaks due to the chosen laser scanning schemes was pointed out. The dressed state picture is employed to elucidate the number of peaks emerged as well as the peak positions in the spectra. The dependence of the generated FWM signal accordingly to the change of parameters, such as Rabi frequencies and frequency detunings of the applied fields, are presented and well explained in the simplified dressed state picture. A prominent increase in FWM intensity is obtained when the Rabi fre-quencies of the coupling and driving field are approximately equal. The frequency detuning of the applied fields causes the shift in the peak positions, peak shape, and even brings about the FWM intensity enhancement.

In this study, the B1Π excited state of NaH has been experimentally studied for the first time. Pulsed laser-induced fluorescence excitation spectroscopy was used to investigate the B1Π electronic state of NaH. A total of 48 ro-vibronic transitions were observed, including within the B–X (0–0) and B–X (0–1) transition bands. Only one B-state vibrational level was identified, and a series of PQR lines, with eight e-parity and eight f-parity sublevels (v′ = 0, J′ = 1–8), were assigned. The level assignment was supported by a comparison of the experimental line positions with the ab initio calculations, the dispersed laser-induced fluorescence spectrum of the NaH B1Π → X1∑+ emission, and the V-type optical–optical double resonance spectra. The Dunham-type coefficients, the mean internuclear distance, the harmonic vibrational frequency ω, and the dissociation energies D0 and De of the B1Π state were determined.

The effect of polarization on the ladder-type electromagnetically induced transparency (EIT) spectra of 133Cs atoms at room temperature for the transitions 62P1/2-62P3/2-112S1/2 is experimentally studied. The entire spectra with additional peaks arising from the Doppler effect are observed. As the relative angle between the probe’s and coupling’s plane of polarization arranges at 0°, 45°, and 90°, the peak height ratio of 44′3" to 44′4" increases by more than 7 times with corresponding values of 0.19, 0.69, and 1.4. Meanwhile, that of 45′4" to 44′4" are found to be 0.61, 0.87, and 1.23 (doubled), respectively. A theoretical model built to explain the experimental results with the considerations of optical pumping effect, two-photon transition probability, dephasing rate, and integration all over the velocity distribution. The simulation and experimental results are well-agreed.

The effect of polarization on the ladder-type electromagnetically induced transparency (EIT) spectra of 133Cs atoms at room temperature for the transitions 62P1/2-62P3/2-112S1/2 is experimentally studied. The entire spectra with additional peaks arising from the Doppler effect are observed. As the relative angle between the probe's and coupling's plane of polarization arranges at 0°, 45°, and 90°, the peak height ratio of 44'3" to 44'4" increases by more than 7 times with corresponding values of 0.19, 0.69, and 1.4. Meanwhile, that of 45'4" to 44'4" are found to be 0.61, 0.87, and 1.23 (doubled), respectively. A theoretical model built to explain the experimental results with the considerations of optical pumping effect, two-photon transition probability, dephasing rate, and integration all over the velocity distribution. The simulation and experimental results are well-agreed.

We report the saturation spectroscopy of carbon dioxide inside a hollow glass waveguide (GW) using a tunable mid-infrared difference frequency generation (DFG) source. This DFG source was generated in a periodically poled lithium niobate crystal with a tuning range from 3.97 to 4.71μm. Saturated spectroscopy was performed on the R(60) transition of CO20001 ← 0000 band at 4.2μm inside a hollow GW of diameter 300μm and length 1 m. The saturation dip signal was found with a pump power as low as 0.18 mW inside the hollow GW. The linewidth of the dip was determined to be 4.40 MHz.

We present a 445-nm InGaN blue diode laser in wavelength-tunable Littrow-type external cavity with a single longitudinal mode output, and a linewidth of 4.7 MHz. Its tuning range was estimated at 4 nm. The maximum output power was up to 20 mW, and the slope efficiency was approximately 0.36 W/A. The external cavity-diode laser linewidth was measured as 4.7 MHz with a lasing threshold to 8.1 MHz at higher applied current. The slope of the linewidth broadening with applied currents was calculated as 57 kHz/mA. And the wavelength tuning range was approximately 4.3 nm at low applied current and narrowed to approximately 2.6 nm at high applied current. A blue external cavity diode laser can deliver a single frequency beam within entire operation range.

The mode evolution of an InGaN blue laser diode with operating current and diode temperature was investigated. The spectra of a 445-nm InGaN blue laser diode with operating currents and diode temperatures was recorded using an ultrahigh resolution spectrometer and a scanning Fabry-Perot interferometer. The blue laser diode can deliver a mW-level single frequency beam with about 20 MHz linewidth at nearly above the lasing threshold. And the temperature-dependent wavelength drift was estimated as 0.31 nm for single longitudinal mode operation region. The spectra showed the number of the longitudinal modes increased with raising operating current. Analysis of the mode evolution of a blue laser diode with operating current and diode temperature is important when how to choose the laser diode for specific applications.

The 2 1Π state of NaH has been observed up to the last bound vibrational level using pulsed optical-optical double resonance fluorescence depletion spectroscopy. A total of 20 rovibrational energy levels ( v = 2-4 and J = 1-9) were assigned to this electronic state by means of comparing the successive rovibrational spectra to the eigenvalues of the ab initio potential energy curve. The decrease of background fluorescence near the atomic asymptotic limit Na(3d) + H(1s) is an indication of reaching the dissociation limit of the NaH 2 1Π state. Unobserved rovibrational levels ( v = 0 and 1) are due to poor Franck-Condon overlap of 2 1Π ← A 1Σ+ transition within the accessible rovibrational levels of intermediate A 1Σ+ state of this work.

Vibrational levels (v = 6-42) of the NaH C 1Σ+ state including the inner and outer wells and the near-dissociation region were observed by pulsed optical-optical double resonance fluorescence depletion spectroscopy. The absolute vibrational quantum number is identified by comparing the vibrational energy difference of this experiment with the ab initio calculations. The outer well with v up to 34 is analyzed using the Dunham expansion and a Rydberg-Klein-Rees (RKR) potential energy curve is constructed. A hybrid double-well potential combined with the RKR potential, the ab initio calculation, and a long-range potential is able to describe the whole NaH C 1Σ+ state including the higher vibrational levels (v = 35-42). The dissociation energy of the NaH C 1Σ+ state is determined to be De(C) = 6595.10 ± 5 cm-1 and then the dissociation energy of the NaH ground state De(X) = 15 807.87 ± 5 cm-1 can be derived.

Quantum turbulence associated with wave and vortex dynamics is numerically investigated for a two-dimensional trapped atomic Rydberg-dressed Bose-Einstein condensate (BEC). When the coupling constant of the soft-core interaction is over a critical value, the superfluid (SF) system can transition into a hexagonal supersolid (SS) state. Based on the Gross-Pitaevskii equation approach, we have discovered a new characteristic k−13/3 scaling law for wave turbulence in the SS state, that coexists with the waveaction k−1/3 and energy k−1 cascades commonly existing in a SF BEC. The new k−13/3 scaling law implies that the SS system exhibits a negative, minus-one power energy dispersion (E ~ k−1) at the wavevector consistent with the radius of the SS droplet. For vortex turbulence, in addition to the presence of the Kolmogorov energy k−5/3 and Saffman enstrophy k−4 cascades, it is found that large amount of independent vortices and antivortices pinned to the interior of the oscillating SS results in a strong k−1 scaling at the wavevector consistent with the SS lattice constant.

We investigate quantum turbulence in a two-dimensional trapped supersolid and demonstrate that both the wave and vortex turbulence involve triple rather than dual cascades, as in a superfluid. Because of the presence of a second gapless mode associated with translation symmetry breaking, a new k^-13/3 scaling law is predicted to occur in the wave turbulence. Simultaneous fast vortex-antivortex creation and annihilation in the interior of the oscillating supersolid results in a k^-1 scaling law in the vortex turbulence. Numerical simulations based on the Gross-Pitaevskii equation confirmed the predictions.

Stimulated emission pumping with fluorescence depletion spectroscopy is used to determine the NaD X 1Σ+ ground-state dissociation energy and its isotopic shift. A total of 230 rovibrational levels in the range 9 ≤ v″ ≤ 29 and 1 ≤ J″ ≤ 11 are observed, where v″ = 29 is about 50 cm-1 below the dissociation limit. Analysis of the highest five vibrational levels yields the dissociation energy De = 15 822 ± 5 cm-1 with a vibrational quantum number at dissociation vD = 31.2 ± 0.1. The energy difference in the well depth of this isotopologue with respect to that of NaH is δDe = De(NaH) - De(NaD) = -7 cm-1. A new set of Dunham coefficients is derived to fit all the observed energy levels to within the experimental uncertainty.

Based on mean-field Gross-Pitaevskii and Bogoliubov-de Gennes approaches, we investigate excitations of a one-dimensional soft-core interacting ultracold Bose gas under the effect of an optical lattice. It is found that no matter how deep the lattice is, at q -> 0 the lowest mode corresponds to a gapless phonon, omega(2)(1) = nu(2)(1)q(2), whereas the second lowest mode corresponds to a gapped optical phonon, omega(2)(2) = Delta(2) +/- nu(2)(2)q(2). Determination of the velocities nu(1), nu(2), the gap Delta, and the possible sign change in omega(2) upon the change of lattice depth can give decisive measures to the transitions across various supersolid and solid states. The power law nu(1) similar to (f(s))(1/2) with f(s) the superfluid fraction is identified in the present system at the tight-binding regime.

We investigate the intrinsic-to-extrinsic supersolid (SS) transition in a lattice ultracold Bose gas with strong long-range interaction. When changing the depth of the periodic lattice potential, the transition is shown to manifest in the ground-state wave function and energy, the change of superfluid fraction ${f}_{s}$, and a roton instability. Near the transition in the extrinsic SS phase, due to the competition between the long-range interaction and the periodic potential, we show that there exist a variety of stable fractionally modulated states (FMSs) upon the change of the effective length of the long-range interaction. Consequence of the transition across different FMSs is discussed.

Ladder-type electromagnetically induced transparency (EIT) and two-photon absorption (TPA) under a low-light level of probe (0.2 mu W/cm(2)(0.06 Gamma(2))) and weak coupling power for a cesium atom at room temperature are investigated. Reduction of the fluorescence on the TPA in a three-level system via EIT interference is clearly observed and analyzed under the low probe Rabi frequency of about 0.30 MHz to avoid the affects from the vicinity of intermediate hyperfine states. The transparency ratio of EIT derived from the reduction of fluorescence is about 25%. Additionally, the EIT linewidth observed can be as narrow as 2.64 MHz, while the coupling Rabi frequency is around 2.66 MHz. By solving the steady-state optical Bloch equations, the numerical simulation spectra are in good agreement with EIT and TPA. According to our investigations, the Doppler velocity averaging effect over the thermal atoms reducing the linewidth of the EIT signal proves the advantage of observing the EIT in the room-temperature cell. (C) 2014 Optical Society of America

New scheme of a real-time all-optical switching (AOS) was demonstrated as the fluorescence signal of cesium two-photon transition (TPT) with the control field. This work explored the optical phenomenon of the TPT with the control field that shares a common excited state, in which the TPT fluorescence is quenched under the control field intensity. The strong stimulated emission due to the control laser suppresses the TPT fluorescence, working as an optical switch. A “NOT gate” is generated for realization of AOS. The power spectrum of the intensity range, which can be used for the AOS, is determined.