Dye Laser Frequency Research Articles

A linewidth-narrowed and frequency-stabilized dye laser for application in laser cooling of molecules.

We demonstrate a robust and versatile solution for locking the continuous-wave dye laser for applications in laser cooling of molecules which need linewidth-narrowed and frequency-stabilized lasers. The dye laser is first stabilized with respect to a reference cavity by Pound-Drever-Hall (PDH) technique which results in a single frequency with the linewidth 200 kHz and short-term stabilization, by stabilizing the length of the reference cavity to a stabilized helium-neon laser we simultaneously transfer the ± 2 MHz absolute frequency stability of the helium-neon laser to the dye laser with long-term stabilization. This allows the dye laser to be frequency chirped with the maximum 60 GHz scan range while its frequency remains locked. It also offers the advantages of locking at arbitrary dye laser frequencies, having a larger locking capture range and frequency scanning range to be implemented via software. This laser has been developed for the purpose of laser cooling a molecular magnesium fluoride beam.

Signatures of coherent propagation of blue polaritons in Cu2O

Double resonant sum-frequency generation (SFG) is demonstrated in Cu${}_{2}$O. The $1S$ yellow orthoexciton-polariton is resonantly excited by a single frequency dye laser (quadrupole transition) and coupled to the blue $1S$ exciton-polariton by a single frequency infrared laser (dipole transition). Sum-frequency (SF) spectra as a function of the energy of the infrared laser are measured for the two pump laser beams parallel and antiparallel. In the antiparallel configuration, pronounced oscillations are observed with a period scaling inversely with the crystal length. The origin of these oscillations is discussed in detail and attributed to a phase-matching effect. The appearance of phase matching can be understood if the blue polaritons---generated by SFG---move coherently through the crystal. This observation is very surprising, since blue exciton-polaritons excited in a one-photon transmission experiment exhibit an absorption length of only $100\phantom{\rule{4.pt}{0ex}}\text{nm}$ due to strong scattering.

Lifetime measurements of odd-parity high-excitation levels of Sm ii by time-resolved laser spectroscopy

Natural radiative lifetimes of 53 odd-parity highly excited levels of singly ionized samarium in the energy range 26 599.08–36 107.66 cm −1 have been measured by the time-resolved laserinduced fluorescence technique in an ionic plume produced by laser ablation. The fundamental frequency and second harmonic of a dye laser have been adopted as the tunable exciting source (308–650 nm), and a fast detection system has been used to record fluorescence signals. The lifetime values obtained in this paper are in the range 10.5–271 ns. A good agreement between the present results and the previously published values was achieved. This work will be useful for investigating the composition of chemically peculiar stars.

Four‐photon laser spectroscopy of fused quartz and crown glass at 0–60 GHz

AbstractThe low wavenumber spectra of fused quartz and crown glass K8 in the range 0.1–2 cm−1 at room temperature were measured by the four‐wave mixing technique. The experimental scheme is based on using both second harmonics of a neodynium‐doped yttrium aluminium garnet (Nd:YAG) pulsed laser and dye laser as a tuning source. The pulse‐to‐pulse deviation of the dye laser frequency is used to obtain the derivative spectra as an additional data source. It was established that the spectra contain a number of narrow (⩽0.1 cm−1) lines. The data could be fitted only by assuming that the Brillouin resonances on longitudinal and transverse sound, as well as the distinct resonances at ∼1.5 cm−1, which can be attributed to hydroxyl (OH) molecular rotations, were involved in the four‐photon scattering process. The fine structure of the Rayleigh wing scattering in fused quartz was observed for the first time. The detected lines, 0.165 cm−1 and 0.26 cm−1 (5.0 and 7.8 GHz, respectively), are attributed to the spheroidal modes ν20 and ν30 of SiO2 spheres with a diameter 880 ± 30 nm. The closely lying eigen modes ν00, ν10 and ν12 are unresolved with a central peak at ± 0.1 cm−1. The 0.4 cm−1 resonance lines in crown glass is attributed to be a manifestation of four‐photon scattering from a second sound phonon. Copyright © 2007 John Wiley & Sons, Ltd.

Sodium UV modeless laser excitation for PLGS

In the framework of Laser Guide Star projects and more particularly of VASAO project of the Canada France Hawaii Telescope, we have developed a modeless laser at 330 nm and we have carried out photometry experiments in laboratory, in order to evaluate the feasibility of the sodium atom excitation at 330 nm. Our modeless laser is a DCM dye laser frequency doubled by a BBO crystal. A high efficiency acousto-optical crystal assures the modeless property. We present the experimental results of sodium atom excitation of 3S1/2 4P3/2 transition at 330.24 nm and 3S1/2 3P3/2 transition at 589 nm. The rate equation model gives a good interpretation of the experimental results.

Generation of 125 mW frequency stabilized continuous-wave tunable laser light at 295 nm by frequency doubling in a BBO crystal

We have frequency doubled 589 nm laser light from a commercial ring dye laser in an external power enhancement cavity utilizing a BBO crystal. With ∼820 mW of input, 125 mW of UV light at 294.5 nm was produced. By offset locking the fundamental dye laser to an iodine hyperfine transition, we have stabilized the dye laser frequency to better than 50 kHz. This laser has been developed for the purpose of laser cooling an atomic gallium beam.

Compact 2.5-W 10-kHz Nd:YLF-pumped dye laser.

A 10-kHz pulse repetition frequency dye laser, end pumped by a Nd:YLF laser, is reported. This laser was tunable from 590 to 655 nm, and up to 2.55 W of output power was obtained at the 609-nm peak tuning wavelength. By inserting an etalon into the dye laser cavity and frequency doubling using a beta-barium borate crystal, we obtained up to 125 mW of 308-nm single-etalon-mode output, which shows potential for the performance of airborne measurements of tropospheric hydroxyl radical concentrations.

Excitation spectrum of the A0+(5 3P1), B1(5 3P1)←X0+(5 1S0) transitions in the CdHe van der Waals molecule: Spectroscopic characterization of the X0+, A0+, and B1 electronic energy states

The first observation of an excitation spectrum of the A0+(5 3P1), B1(5 3P1)←X0+(5 1S0) transitions in the CdHe van der Waals molecule is reported. A continuous molecular-jet-expansion beam of CdHe seeded in helium was crossed with a pulsed-laser beam produced by a Nd:YAG laser-pumped-dye laser. The dye laser frequency was doubled using a KDP-C crystal and tuned to a frequency in the vicinity of the 5 3P1↔5 1S0 resonance transition in atomic cadmium (λres≈3262.0 Å). The assignment of vibrational bands was obtained with the aid of rigorous computer simulation of the A0+←X0+ and B1←X0+ transitions. The analysis of the excitation spectrum yielded potential parameters of the molecule: De″(X0+)=14.2 cm−1, ωe″(X0+)=9.6 cm−1, ωe″xe″(X0+)=1.63 cm−1 for the ground state, and De′(A0+)=41.2 cm−1, ωe′(A0+)=20.0 cm−1, ωe′xe′(A0+)=2.4 cm−1 as well as De′(B1)=6.1 cm−1, ωe′(B1)=3.6 cm−1, and ωe′xe′(B1)=0.53 cm−1 for the excited states. From a simulation procedure the differences between equilibrium internuclear separations ΔR=Re″(X0+)−Re′(A0+)=−1.50 Å and ΔR=Re″(X0+)−Re′(B1) =+0.12 Å were also obtained. The results were subjected to the LeRoy–Bernstein method to evaluate the C6/R6 long-range potential parameters for the X0+ and A0+ energy states.

Diode laser cavity ring down spectroscopy

We recently demonstrated how in cativy ring down spectroscopy (CRDS) a CW single frequency dye laser may be conveniently employed in place of the pulsed laser of standard CRDS. Here we extend this result to external cavity tunable diode lasers. Compact spectroscopic devices with extreme sensitivity (2 × 10 −10/cm) become a reality. To demonstrate the instrumental resolution we obtained high quality NO 2 spectra in a supersonic slit jet, with a residual Doppler width of about 250 MHz.

Characteristics of a pressure‐tuned single‐mode dye laser oscillator pumped by a copper vapor laser

Frequency tuning based on pressure control is demonstrated on an etalon-narrowed Littrow-type single-mode dye laser oscillator pumped by a copper vapor laser. The oscillator is installed in a pressure vessel and the frequency is scanned by controlling the refractive index of the air inside the vessel. To scan the dye laser frequency continuously without mode hopping, the cavity length is also controlled in addition to the pressure change. The frequency stability of the oscillator in a pressure vessel is within 100 MHz/1.5 hr and the oscillator can be scanned with a frequency range of 29 GHz at a scan rate of around 2.5 GHz/min.

A technique for mapping three-dimensional number densities of species in laser produced plumes

The potential of a diagnostic technique to provide quantitative three-dimensional (3D) density distributions of species in a low temperature laser-produced plume is shown. An expanded, short pulse, tunable dye laser is used to probe the plume at a set time during the expansion. Simultaneous recording of two-dimensional in-line absorbance maps and orthogonal recording of laser induced fluorescence permits the 3D density mapping by scanning the dye laser frequency. Preliminary data, supported by a simple model, is presented for the case of Ba II ions in a YBCO plume heated by a KrF laser.

Laser spectroscopy of even parity Rydberg series of krypton

An optogalvanic detection method has been combined with either CW monomode dye laser excitation or frequency doubled pulsed dye laser excitation, to investigate the even parity spectra of atomic krypton from levels of the 4p54d and 4p55s configurations. The energies of 81 levels belonging to 45nf (J=1 to 5) Rydberg series and 61 levels belonging to 4p5np (J=1 to 3) Rydberg series have been determined. Most of these levels had never been observed previously. A multichannel quantum defect theory treatment of J=1 and J=2 even parity spectra has been performed, completing previously similar studies on odd parity spectra. The first ionization limit position has been redetermined. Taking into account the more recent values of krypton resonance line wavenumbers, this position results in: I32/=112914.41+or-0.02 cm-1; it is in good agreement with previous determinations.

Effect of Laser Characteristics On Thorium Isotopic Ratios Measured By Resonance Ionization Mass Spectrometry

ABSTRACT: We describe our development of resonance ionization mass spectrometry (RIMS) using continuous-wave lasers toward the measurement of isotopic ratios important in geochemistry and geochronology. Specifically, we compare the precision and accuracy of 230Th/232Th isotopic ratios measured by cw RIMS using both broad-band and narrow-band lasers. We also discuss the effectiveness of frequency-stabilizing techniques, i.e., external frequency locking of a broad-band dye laser and computer-controlled frequency centering of a narrow-band Ti:sapphire laser.

Investigations of the precision and accuracy of 2-λ cars and its application in temperature measurements in turbulent flames

The precision and accuracy in temperature measurements made using 2-λ CARS, where two narrow-band dye laser frequencies are used instead of one broad-band profile, are presented. Experimental results from single-shot referencing are presented, together with a brief theoretical analysis. The paper is concluded with a description of results from a practical demonstration of the technique in a premixed bluff body stabilized flame simulating an afterburner in a jet engine.

Frequency locking a dye laser to the central optical Ramsey fringe in a Ca atomic beam and wavelength measurement

The frequency of a dye laser is stabilized to the 3P1–1S0 intercombination line of 40Ca through use of the first-derivative signal of the Ramsey fringes detected in a Ca atomic beam. The long-term stability of the frequency of the Ca-stabilized dye laser is estimated to be a few kilohertz from the servo error signal. The wavelength of the Ca-stabilized dye-laser beam is measured by comparison with that for an I2-stabilized He–Ne laser, which is one of the current wavelength standards. The measured wavelength is evaluated to be 657.4594396 nm with an uncertainty of better than 1 × 10−9.

Rotationally resolved vibrational overtone spectroscopy of hydrogen peroxide at chemically significant energies

An infrared–optical double resonance scheme simplifies the room temperature 6νOH vibrational overtone spectrum of hydrogen peroxide and prepares highly excited reactant molecules in single rotational states for unimolecular reaction studies. First, an optical parametric oscillator excites the OH asymmetric stretch (ν5) and selects a single or small subset of rotational states. A visible dye laser pulse then promotes molecules from vOH=1 to vOH=6 where they subsequently dissociate to produce two OH fragments. A third laser detects the dissociation products via laser induced fluorescence. The rotationally resolved vibrational overtone spectra of hydrogen peroxide generated by scanning the visible dye laser frequency are assignable to a parallel band of a near prolate symmetric top. Linewidths of the individual rovibrational features range from 1–3 cm−1 but show no systematic dependence upon the rotational quantum numbers and are attributed predominantly to anharmonic coupling of the zeroth-order bright state to dark background states. The assignability of the double-resonance vibrational overtone spectra to J and K quantum numbers implies that K is conserved for at least a time determined by the linewidth of a single zeroth-order rovibrational feature.

Four-wave mixing in CO via the C 1?+ (??=0) state

Coherent vacuum ultraviolet (VUV) radiation was generated by four-wave difference frequency mixing (ωVUV=2ω1−ω2) of pulsed dye laser radiation in carbon monoxide (CO). The frequency ω1 was tuned to the C 1Σ+(υ′=0)←X 1Σ+(υ″=0) two-photon transition, while the dye laser frequency ω2 was scaned around 17650 cm−1 which corresponds to the A 1Π(υ=7)«C 1Σ+(υ′=0) transition energy. The VUV intensity was found to be strongly wavelength dependent. The analysis of the spectrum revealed (i) that the VUV intensity was enhanced by the rotational levels of the A 1Π(υ=7) state and (ii) that the off-resonance excitation in the C 1Σ+(υ′=0)←X 1Σ+(υ″=0) two-photon transition greatly contributed to the present four-wave mixing process. The effects of pumping laser detuning, saturation and foreign gases are briefly discussed.

Two-photon resonant processes in atomic barium vapour

Two-photon resonant or nearly resonant optical processes have been investigated in atomic barium vapour ( approximately 1017 cm-3) with a pulse dye laser (frequency omega L) covering the range 735-415 nm. These interactions result in strong coherent emissions emitted either forward and backward, or forward only. The optical processes responsible for these coherent emissions have been identified. Seventy five lines (frequency omega ES) emitted from 1000 to 360 nm are due to optically pumped stimulated emissions or stimulated electronic hyper-Raman scattering. Twenty eight lines (frequency omega sigma ) observed from 795 to 250 nm are generated through four-wave-mixing parametric processes with omega sigma =2 omega L+or- omega ES, and nine- (795-260 nm) through six-wave-mixing parametric processes with omega sigma =2 omega L- omega ES1- omega ES2+or- omega ES3.

Stabilization of a single mode dye laser to a HeNe laser using magnetic modulation of a three-level neon system

We describe a simple stabilization method where a tunable single mode (594.5 nm) cw dye laser is locked to a stabilized (633 nm) HeNe laser via the 1s 5-2p 4-3s 2 Ne transitions. By using longitudinal Zeeman modulation of the absorber and a circularly polarized HeNe laser beam derivative signals are obtained. Utilization of routine lock-in techniques produces a dye laser frequency stability comparable with that of the reference HeNe laser.

Collisions of metastable Ne*, He* atoms with ground-state He, Ne atoms studied by atomic beam and laser techniques

A crossed nozzle-beam experiment is used to investigate thermal energy collisions: Ne*(2p53s,3P0, 2)+He(1s2,1S0), almost purely elastic, and He*(1s2s,1, 3S)+Ne(2p6,1S0), in which inelastic excitation transfers occur. State and velocity selection of the scattered Ne* atoms is performed using a tunablecw dye laser frequency locked on a definite Zeeman component of the transition 1s5→2p6 (λ=614.3 nm) of20Ne or22Ne. In the purely elastic case, this technique allows the selection of one of the two final velocities, and then an unambiguous LAB-CM transformation. The differential cross section at 62 meV tallies on accords with a calculation using a single effective potential. In He* on Ne collisions, the main inelastic processes are endothermic excitation transfers from He*(21S). Experimental results obtained at different energies (62, 95, 109, 124 meV) show that the transfers essentially result in levels 3s and 4d of Ne.