Measurement of the velocity distribution of neutral atoms using laser-induced fluorescence

Laser-induced fluorescence has been used to measure the Doppler-shifted emission spectra in the atomic beam of gadolinium. The velocity distribution of gadolinium atoms that was deduced from these spectra shows good agreement with a Maxwellian distribution. Based on this good agreement, temperatures of the evaporating source have also been estimated. A new experimental method has been devised in our measurements, which can also be used for other multiline systems similar to gadolinium. This method allows one to effectively eliminate the distorting interference present in Doppler profile measurements for the multiline systems mentioned above. The text was submitted by the authors in English.     

An optical conveyor belt for single neutral atoms

Using optical dipole forces we have realized controlled transport of a single or any desired small number of neutral atoms over a distance of a centimeter with sub-micrometer precision. A standing wave dipole trap is loaded with a prescribed number of cesium atoms from a magneto-optical trap. Mutual detuning of the counter-propagating laser beams moves the interference pattern, allowing us to accelerate and stop the atoms at preselected points along the standing wave. The transportation efficiency is close to 100%. This optical ‘single-atom conveyor belt’ represents a versatile tool for future experiments requiring deterministic delivery of a prescribed number of atoms on demand. Received: 6 July 2001 / Published online: 23 November 2001     

Quantitative two-photon laser-induced fluorescence of hydrogen atoms in a 1 kW arcjet thruster

Received: 19 February 1998/Revised version: 31 March 1998     

An efficient method for measuring atomic and molecular lifetimes using a modulated or deflected CW dye laser beam

By pulse modulating or deflecting a CW dye laser beam, cascade-free lifetime determinations at high spectral resolution can be performed with the decayed-coincidence technique using measuring times of about 1 minute. The method is illustrated by lifetime measurements for the $\text{7}{}^2\text{P}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext><mtext>1</mtext><mtext>2</mtext>}}$ levels of cesium.     

Time domain measuring system of molecular fluorescence with real-time monitor and control of pulsed dye laser

A computer controlled system is presented for a high-precision, time-domain measurement of molecular fluorescence induced by a pulsed dye laser field. In this system three intelligent functions are assembled by the system controller: they are an automatic wavelength control of pulsed dye laser to 0.45 GHz resolution, a digital wavelength meter of 10^–7 precision, and a high-speed waveform digitizer with 10 ps inherent resolution. Then the system achieves a unique capability such as to record real-time data of fluorescence decay in the nanosecond regime under an on-line monitor and control of the laser wavelength to milliangstrom precision. The basic constitution and practical performance of the system are described with particular emphasis on its high precision and multi-task capability.     

High resolution fluorescence spectroscopy by use of a CW dye laser

The hyperfine structure of the Na D₂-line was investigated in a fluorescence experiment involving a narrow band tunable dye laser and a highly collimated atomic beam. The observed linewidth was less than 16 MHz (natural line-width 10 MHz). All hyperfine components were resolved.     

Possible excitation of a fast sodium beam by laser irradiation

We present results of model calculations concerning the fraction of excited atoms obtained by laser irradiation of a fast sodium atom beam (100–400 eV kinetic energy). We calculated relative absorption probabilities as a function of the intersection angle between the two beams, the atom-beam energy, the atom-beam energy spread and the atom-beam divergence. The fraction of excited atoms that can be obtained at 300 eV is at least a factor of 5 smaller than in the case of a thermal beam, due to the divergence and energy spread of the fast atom beam giving rise to a large Doppler broadening.     

A subpicosecond dye laser pumped by a xenon ion laser

A pulsed xenon ion laser has been used to pump a rhodamine 6G dye laser utilizing a ring resonator. The dye laser has been passively mode-locked; a pulsewidth of 0.5 ps and a 50 kW peak power have been obtained.Work partly supported by Italian C.N.R.     

Active mode locking of a high pressure CW waveguide CO2 laser

In this paper, we report on a new concept for active mode locking of lasers. It has been successfully applied to a cw waveguide CO₂ laser and pulse widths as short as 2 ns have been obtained.     

Achievement of laser fusion of biological cells using UV pulsed dye laser beams

This paper reports a successful achievement of laser-induced biological cell fusion using an excimer laser excited dye laser. To our knowledge, we examined for the first time the dependence of fusion rate on laser pulse energy, number of laser pulses, and laser wavelength. Maximum fusion rate of approximately 50% was obtained by this laser fusion technology.     

Schlieren diagnostics of the plasma focus using a mode-locked dye laser

By means of schlieren techniques the discharge characteristics of a 1 kJ plasma focus device were investigated. Different inner electrodes were used with diameters ranging from 4 mm to 10 mm and the working gases were hydrogen and neon. A spatial resolution in the m region and a temporal resolution in the ps region could be achieved using a mode-locked dye laser as schlieren light source. During the run-down and collapse phase of the discharge the spatially and temporally resolved electron density was determined from the schlieren pictures by means of numerical simultations of the beam deflection by the plasma. During the focus phase the temporal development of the plasma could be observed.     

Comparative study of spectral narrowing of a pulsed Ti:Sapphire laser using pulsed and CW injection seeding

We report a comparative study of a pulsed as well as continuous-wave (cw) injection seeding of a Ti:Sapphire laser pumped by aQ-switched frequency-doubled Nd³⁺:YAG laser for achieving narrow spectral bandwidth. The results have indicated that the Ti:Sapphire laser using either a pulsed or a cw injection seeding could achieve efficient energy extraction in a narrow spectral bandwidth. In the case of pulsed injection seeding, the injection energy required for the complete injection seeding critically depended upon the timing of the Ti:Sapphire laser with respect to the delayed onset of the slave laser. On the other hand, in the case of cw injection seeding, the spectral bandwidth of the Ti:Sapphire laser was efficiently narrowed down to approximately 0.01 cm^–1 with an injection power of less than 1 mW. In both types of injection seeding, characteristics observed experimentally were compared with those obtained by a numerical simulation code based on the one-dimensional rate-equation model.     

High-speed machining of glass materials by laser-induced plasma-assisted ablation using a 532-nm laser

+ :YAG laser (532 nm). The plasma generated from a silver (Ag) target by the laser irradiation effectively assists in ablation of the fused quartz substrate by the same laser beam, although the laser beam is transparent to the substrate. A grating with a cross-sectional shape like a square-wave (period ≈ 20 μm) is achieved using the mask projection technique. The ablation rate reaches several tens nm/pulse. In addition, LIPAA is applied to high-speed hole drilling (700 μm in diameter) of fused-quartz (0.5 mm thick) and Pyrex glass (0.5 mm thick). Received: 25 May 1998/Accepted: 19 June 1998     

Statistical properties of laser-induced fluorescence signals

We point out the influence of the different noise sources which occur in the detection of the fluorescence signal induced by a laser in an atomic beam. We have developed a theoretical model which takes account of the atomic shot noise, photon noise, laser-frequency noise and a partition noise linked to the imperfect detection of the fluorescence photons. The calculations have been performed for two- and three-level atomic systems. We detail the own contribution of each noise source and give some predictions concerning the value of the fluorescence signal to noise ratio. We determine predominance domains of each noise source which depend on the values of key parameters such as the atomic flux intensity and the laser spectral linewidth. We particularly show that the laser-frequency noise, which induces a coupling between the emission of fluorescence photons by various atoms, leads to a saturation of the S/N ratio for intense atomic fluxes. Moreover, we point out that the optical pumping process associated with a three level atomic system leads to an interesting laser-noise filtering effect.     

Coherence and beam geometry of a superradiant dye laser

This paper reports the observation of a well defined radiation mode emitted from a superradiant dye laser pumped by a pulsed nitrogen laser. Beam geometry and spatial coherence of the dye laser are studied in connection with the pumping geometry. It is shown that under favorable pumping conditions most of the excited molecules radiate into the same spatial mode by stimulated emission. The associated mode structure is also calculated based on a model of a properly phased dipole distribution. The calculated emission pattern reproduces the observed far field pattern closely. Work supported in part by CNPq and FINEP.     

Direct absorption spectroscopy using a rapidly tunable CW dye laser

Using a recently developed electronically tunable cw dye laser, the spectrum of an absorption sample could be obtained and repeatedly scanned every 10 μsec. The system is potentially capable of monitoring spectral changes in times as short as 10^?7 sec.     

Frequency locking of a dye laser using adsorbed atoms

Frequency locking of a dye laser to atomic lines is obtained by using atoms adsorbed on an intracavity glass surface. This effect is attributed to the selective transmission of the interface due to anomalous refractive index.     

Simultaneous two-line operation of a CW CO laser with arbitrary choice of laser transitions

An experimental scheme is discussed, by which we can operate a CO laser at two individually selectable lines from the same gain tube. There are virtually no restrictions on the wavelength separation of the two lines within the manifold of the available lasing transitions. Experimental verifications of this scheme are described and the mutual influence of the simultaneous laser operation is discussed.Dedicated to Professor Siegfried Penselin on the occasion of his 60th birthday     

Calibration of imaging laser-induced fluorescence measurements in highly absorbing flames

It has been described earlier that imaging measurements of laser-induced fluorescence (LIF) in flames can be calibrated to number densities with an integrated absorption measurement provided the integrated absorption is small. In this paper a method is presented that extends the technique to flames with substantial absorption, improves the number density determination and allows the experimental parameters to be chosen more freely. The method is based on an iterative computer procedure that reconstructs the 1-D spatially resolved absorption profile from laser measurements of the 1-D spatially resolved LIF and the integrated absorption of the laser beam. The technique is experimentally demonstrated by measurements of OH number densities in atmospheric flames. It is potentially a single-pulse method. Other applications of the iterative procedure are mentioned.     

A novel picosecond distributed feedback dye laser arrangement for excimer laser pumping

A distributed feedback dye laser arrangement is described which can generate pulses at the subharmonic wavelengths of the main excimer laser lines (308 nm, 248 nm, 193 nm, etc.). The laser can be pumped with broadband lasers, such as the XeCl^* laserpumped dye laser with competing cavities. The laser is designed to be used as a part of a femtosecond, terawatt excimer laser system.