kHz Linewidth Research Articles

Tunable laser with partial reflectors

This paper describes the theory, modelling and design of a simple tunable laser with a 15–20 nm quasi-continuous tuning range, 30 dB side mode suppression ratio, 400 kHz linewidth and low variation in output power. Prototype fabrication has used focussed ion beam etching to modify standard Fabry–Perot structures. The laser has four electrically isolated sections separated by reflection/scattering sites with power reflectivity of about 1%. Tuning is achieved by changing the currents to each section and hence altering the refractive indices.

Structure and Properties of Acidic Protons in Anhydrous Dodecatungstophosphoric Acid, H3PW12O40, As Studied by Solid-State 1H, 2H NMR, and 1H−31P Sedor NMR

The binding position and the electronic properties of acidic proton in anhydrous dodecatungstophosphoric acid, H3PW12O40, were studied by means of 1H, 2H NMR, and 1H−31P spin−echo double resonance (SEDOR) NMR techniques. 1H broad line NMR spectrum showed a bell-type resonance line shape with 4.7 kHz line width and MAS NMR spectrum has a single resonance peak, suggesting that the hetero-polyanion PW12O403- provides a single site to the acidic proton. 2H NMR spectrum leads to the quadrupole coupling constant (QCC) of 210 kHz and the asymmetry parameter of the electric-field-gradient tensor (η) of 0.15. The value of QCC suggests that the deuterons are bonded to oxygen atoms in the hetero-polyanion very rigidly, and that any motion of the hetero-polyanion does not take place. A remarkable decay of the 1H−31P SEDOR signal was observed, due to the dipolar interaction between the central 31P and three protons strongly bonded to the hetero-polyanion. The P−H distance was evaluated by simulating the decay behavior...

High-resolution, >1 GHz NMR in unstable magnetic fields.

Resistive or hybrid magnets can achieve substantially higher fields than those available in superconducting magnets, but their spatial homogeneity and temporal stability are unacceptable for high-resolution NMR. We show that modern stabilization and shimming technology, combined with detection of intermolecular zero-quantum coherences (iZQCs), can remove almost all of the effects of inhomogeneity and drifts, while retaining chemical shift differences and J couplings. In a 25-T electromagnet (1 kHz/s drift, 3 kHz linewidth over 1 cm(3)), iZQC detection removes >99% of the remaining inhomogeneity, to generate the first high-resolution liquid-state NMR spectra acquired at >1 GHz.

An advanced technology for a new generation of Cold Atom Space Clock (Pharao)

In 1994, the CNES initiated an ambitious Technology and Research Program in preparation of a new space clock development, the PHARAO project (PHARAO: Projet d'Horloge Atomique a̧ Refroidissement d'Atomes en Orbite). PHARAO has been selected by ESA to be flown on an external Express Pallet of the International Space Station during the early utilisation phase. PHARAO is one of the main components of the European payload called ACES (Atomic Clock Ensemble in Space). This Cesium clock, using specific laser technics for cooling the atoms, is able to reach levels of stability and accuracy in the range 10 −16 – 10 −17, which have never been achieved yet. But such performances do require an advanced technology, because off-the-shelf equipment would not fulfill the drastic specifications required for PHARAO. The paper presents the preliminary design of the PHARAO flight version which is currently based on new developments such as: • - an ultra-stable quartz oscillator at 10 MHz • - a low phase noise synthesis chain • - a laser with 100 KHz linewidth.

Narrowband Excitation of 2H Powder Pattern and Its Application to 2H 1D Exchange Sample-Turning NMR

Frequency-selective narrowband excitation of the 2H powder pattern was examined. Selection of a single spectral band with a linewidth of ca. 15 kHz was achieved by a narrowband 1H → 2H cross polarization by using the time-averaged precession frequency method. Further narrowing with a ca. 5 kHz linewidth is achieved by DANTE irradiation. The narrowband excitation was applied to transform a recently developed 2D spin-exchange method for obtaining structural information (Chem. Phys. Lett. 260, 159, (1996)) into its 1D analogue. The determination of the D–C–D bond angle was demonstrated for α-glycine-[2,2-d2]. Further, the intermolecular polarization transfer between two deuterons separated by 0.299 nm was detected with the mixing time of 500 ms.

A sideband-injection locked extended cavity diode laser for interrogating cold trapped Strontium ions

A simple optical sideband injection locking technique is demonstrated to frequency offset-lock a 674 nm slave extended cavity diode laser to a single frequency source. By injecting light from a master laser into either sideband of the frequency modulated extended cavity slave laser, it is shown that the carrier of the slave is frequency locked to the master laser with a relative linewidth much less than 10 Hz. The locking bandwidth is investigated to determine the largest capture range. An observation of the 674 nm 2 S 1/2– 2 D 5/2 transition in a single ion of 88 Sr + was performed using this laser system, yielding ≈1 kHz linewidth Zeeman structure, limited by the master laser linewidth. National Physical Laboratory

Highly efficient cw frequency doubling of 854 nm GaAlAs diode lasers in an external ring cavity

We report on 50% conversion efficiency for frequency doubling of a 854 nm GaAlAs diode laser using a potassium niobate crystal in an external ring cavity. Frequency stabilization of the diode laser is achieved by direct optical feedback from the doubling cavity or from a grating in Littrow configuration. We determine 200 kHz linewidth from the measured spectral density of the frequency noise and from a beat signal measurement of two independent diode lasers. The blue output power of 7.8 mW shows rms-fluctuations of less than 0.6% in 1 MHz bandwidth.

Velocity Measurement of Free Jets Using Nuclear Hyperfine Structure of I2.

Axial velocity distribution in an I2-seeded Ar free jet is investigated by the laser-induced fluorescence(LIF)technique using a ring dye laser with 500 kHz line width. Since the translational temperature in the flow region is low, the hyperfine structure due to the nuclear spin of I2 molecules is observed in the spectrum of I2 B-X bands. The spectrum shape is explained by the quantum mechanical theory and the simulated spectra coincide with our measurements. First, the possibility of the translational temperature measurement based on the hyperfine spectrum shape is discussed. Then, axial velocity measurement is performed and the results are found to be in good agreement with those of Ashkenas & Sherman. The applicability and the velocity resolution limit of our measurement technique are also discussed.

Velocity Measurement of Free Jets using Nuclear Hyperfine Structure of I2.

Axial velocity distribution in an I2-seeded Ar free jet is investigated by the laser-induced fluorescence (LIF) technique using a ring dye laser with 500 kHz linewidth. Since the translational temperature in the flow region is low, the hyperfine structure due to the nuclear spin of I2 molecules is observed in the spectrum of I2B3II+ouhX1Σ+g bands. The spectrum shape is explained by the quantum mechanical theory and the simulated spectra coincide with our measurements. First, the possibility of the translational temperature measurement based on the hyperfine spectrum shape is discussed. Then, axial velocity measurement is performed and the results are found to be in good agreement with those of Ashkenas & Sherman. The applicability and the velocity resolution limit of our measurement technique are also discussed.

Fast imaging in liquids and solids with the Back-projection Low Angle ShoT (BLAST) technique

A simple fast imaging scheme is proposed, which is applicable to solid- and liquid-like materials. It is based on low angle pulse excitation in combination with back-projection reconstruction and proper data handling and is called Back-projection Low Angle ShoT (BLAST) technique. The sequence is applied to grape as a biological sample and to a jellibaby (2 kHz linewidth at half intensity) for demonstration of the applicability to solid objects.

Acyl chain orientational order in large unilamellar vesicles: comparison with multilamellar liposomes: a 2H and 31P nuclear magnetic resonance study

Large unilamellar vesicles (LUVs) composed of 1-[2H31]palmitoyl-2-oleoyl phosphatidylcholine (POPC-d31), with diameters of approximately 117 +/- 31 and 180 +/- 44 nm, were prepared by extrusion through polycarbonate filters with pore sizes of 0.1 and 0.2 microns, respectively. The 2H nuclear magnetic resonance (NMR) spectra obtained at 21 degrees C contain two components: a broad component (approximately 17 kHz linewidth) corresponding to the methylene groups and a narrower component originating from the methyl groups. Spectra with increasing powder pattern characteristics were obtained by reducing the rate of phospholipid reorientations by addition of glycerol (to increase the solvent viscosity) and by lowering the temperature. Full powder spectra, characteristic of liquid-crystalline bilayers, were obtained for both LUV samples at 0 degrees C in the presence of 50 wt% glycerol. Individual quadrupolar splittings were not resolved in these spectra, due to broader linewidths in the LUVs, which have significantly shorter values for spin-spin relaxation time T2 measured from the decay of the quadrupolar echo (90 microseconds) than the multilmellar vesicles (MLVs; 540 microseconds). Smoothed order parameter profiles (OPPs) were obtained for these samples by integration of the dePaked spectra. The OPPs were very similar to the OPP of POPC-d31 MLVs in 50 wt% glycerol at the same temperature, indicating that orientational order in MLVs and LUVs with a diameter of > or = 100 nm is essentially the same. The presence of 80 wt% glycerol was found to have a disordering effect on the vesicles.

Integrated all optical fibre source of multigigahertz soliton pulse train

A 59.1 GHz train of 2.2 ps solitons with low phase noise (<5×10−5) is generated by a novel, passive, all optical fibre source. The technique is based on transformation of a dual frequency beat signal generated by a 16 kHz line width erbium fibre DBR laser having a selectable and highly stable frequency separation, into a soliton train in a comblike dispersion profiled fibre, a novel fibre design which uses conventional optical fibres.

Diffusion and spatially resolved NMR in Berea and Venezuelan oil reservoir rocks

Conventional and spatially resolved proton NMR and relaxation measurements are used in order to study the molecular motions and the equilibrium and nonequilibrium diffusion of oils in Berea sandstone and Venezuelan reservoir rocks. In the water-saturated Berea a single line with T 2 ∗ ⋍ 150 μ sec is observed, while the relaxation recovery is multiexponential. In an oil reservoir rock (Ful 13) a single narrow line is present while a distribution of relaxation rates is evidenced from the recovery plots. On the contrary, in the Ful 7 sample (extracted at a deeper depth in a different zone) two NMR components are present, with 3.5 and 30 KHz linewidths, and the recovery plot exhibits biexponential law. No echo signal could be reconstructed in the oil reservoir rocks. These findings can be related to the effects in the micropores, where motions at very low frequency can occur in a thin layer. From a comparison of the diffusion constant in water-saturated Berea, D ⋍ 5 × 10 −6 cm 2/sec , with the ones in model systems, the average size of the pores is estimated around 40 Å. The density profiles at the equilibrium show uniform distribution of oils or of water, and the relaxation rates appear independent from the selected slice. The nonequilibrium diffusion was studied as a function of time in a Berea cylinder with z axis along H 0, starting from a thin layer of oil at the base, and detecting the spin density profiles d( z, t) with slice-selection techniques. Simultaneously, the values of T 1's were measured locally, and the distribution of the relaxation rates was observed to be present in any slice. It turns out that water is diffusing at a fast rate, while oil diffuses three orders of magnitude slower. The continue source diffusion does not follow a simple Fickian law, while the finite source diffusion shows a pluglike propagation.

Optical generation, distribution, and control of microwaves using laser heterodyne

Demonstrated is the optical generation and transmission of a microwave signal by the mixing of two high-quality optical signals from diode-laser-pumped Nd:YAG ring lasers, resulting in a narrow microwave line width (less than 5 kHz line width at 3 dB and less than -115 dBc/Hz at 300 kHz from line center) and broad microwave tunability (DC to 52 GHz). A III-V semiconductor waveguide with a doping superlattice active region is used to optoelectronically provide 20 dB of amplitude control and up to 5 pi of phase shift. This approach can be straightforwardly implemented using integrated optics and fiberoptic links for control of phased-array antenna elements. >

Travelling-wave erbium fibre ring laser with 60 kHz linewidth

Operation of an erbium-doped-phospho-alumino-silicate-fibre ring laser in a unidirectional travelling-wave configuration enables narrow linewidth, single frequency emission to be obtained at a wavelength of 1.555 mu m. A 60 kHz linewidth has been measured. >

Optically stabilized narrow linewidth semiconductor laser for high resolution spectroscopy

A narrow bandwidth tunable semiconductor laser system operating near 780 nm is described. The commercial laser diodes are frequency stabilized by optical feedback from an external, confocal Fabry-Perot resonator. The feedback phase is electronically stabilized to improve the frequency stability. A beat signal with 30 kHz linewidth between two identical, independent systems is recorded. The performance of this system is demonstrated in a laser cooling experiment with rubidium.

Wavelength-tunable single-frequency and single-polarisation er-doped fibre ring-laser with 1.4 kHz linewidth

A narrow linewidth of 1.4 kHz with single frequency operation is demonstrated in an Er-doped fibre ring-laser. A stable lasing spectrum can be achieved using a single polarisation fibre-cavity. An optical bandpass filter incorporated in the ring-cavity makes the lasing wavelength tunable, and a 2.8 nm tuning range is demonstrated.

Spectral linewidth broadening in Er-doped-fibre amplifiers measured with less than 1.4 kHz linewidth light source

Spectral linewidth broadening in Er-doped-fibre amplifiers is measured by utilising a delayed self-heterodyne interfero-meter with 1.4 kHz resolution in the 1550 nm range. Though the noise floor is broadened, no broadening is observed at the 3 dB down point.

Infrared absorption and microwave–infrared double resonance studies of Ne⋅OCS molecular beams

Infrared absorption spectra for molecular beams of Ne⋅OCS have been observed with a diode laser for the vibrational transition near 2062 cm−1 correlating with the monomer ν3 mode. The linewidths were ∼150 MHz (FWHM), giving rotationally resolved spectra and allowing the upper and lower vibrational state A, B, and C rotational constants to be determined along with the frequency of the band origin. No broadening in excess of that expected from Doppler effects and laser linewidth was observed, setting a lower limit of 10−9 s on the lifetime of the upper state. Rotational transitions for the vibrational ground state were observed by microwave–infrared double resonance experiments. The ∼150 kHz linewidths in these experiments increased the precision of the rotational constants and permitted the quartic centrifugal distortion constants for the ground state to be determined. The effective structure of the Ne⋅OCS complex was calculated from the rotational constant data. The vibrational frequency and structural results are discussed in relation to similar work on other rare gas–OCS complexes.

Fibre Bragg reflector for mode selection and line-narrowing of injection lasers

A surface-relief grating on a side-polished single-mode fibre acts as an external Bragg reflector for standard, multilongitudinal-mode 1.3 μm injection lasers. With 2 m fibre length, single-mode, 60 kHz linewidth operation at 1 mW is obtained.