NaK 22Σ+ → 11Σ+ band optically pumped laser near 1.02 μm

Optically pumped laser emission has been observed on the NaK 2(A)¹⁺ 1(X)¹⁺ electronic state transition. The emission occurs between 1.015 and 1.035 m when a sodium-potassium heat-pipe oven is pumped with 695–745 nm pulsed dye laser radiation. The laser emission occurs on many ro-vibrational transitions without the use of cavity mirrors. However, the addition of a simple cavity increases both the number of observed lasing transitions and the amplitude of the emission on each line. We report our results for the dependence of the emission intensity on pump laser power, oven temperature, and buffer gas pressure.     

К процессам в электро дных оБластях в силъноточных кратк овременных электрических разря дах

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On processes in electrode spaces of short-time high-intensity electric discharges

The conditions and causes of the interrupted emission of the vapours of the material of short-time high-intensity electric discharge electrodes are discussed on the basis of earlier and new observations.

     

Pulsed 532 nm laser wirestripping: Removal of dye-doped polyurethane insulation

Removal of rhodamine 6G doped polyurethane insulation coated onto 50 m diameter wire is shown to proceed efficiently and cleanly by irradiation with 532 nm Q-switched pulses from a Nd:YAG laser. The stripping action produced by this method is similar in quality to excimer laser wirestripping. Several experimental parameters were explored including fluence, pulse duration, dye concentration, and the number of incident pulses. Acceptable stripping conditions were obtained for a 3–5 s exposure at 10 Hz, using a dye concentration of 10% by weight, and 12 n pulses at 650 mJ/cm². Nearly 0.5 m/pulse is removed at this fluence, which exceeds the threshold fluence of 600 mJ/cm² by only 50 mJ/cm². The measured 532 nm absorption coefficient of the 10% dye-doped polyurethane was 4×10⁴ cm^–1. Lower fluences and/or dye concentrations produced inadequate stripping, while shorter duration pulses caused unacceptable melting of the thin gold layer which covered the copper core of the wire. Pulse-by-pulse photographs of the stripping action clearly show melting of the dye/polymer insulation, and thermal rollback of the insulation near the stripped end. Regardless, excellent edge definition is obtained by this method.     

Effects of Buffer Gas N2 on Miniature Optically Pumped NH3 Submillimeter Wave Cavity Laser Emission at 67.2 μm

The effect of buffer gas N₂ on miniature optically pumped NH₃ submillimeter wave (SMMW) cavity laser emission at 67.2m was studied theoretically and experimentally. It has been found that: 1. N₂ had a positive effect on laser output of 67.2m, 2. sharp absorption in laser spectrum under certain gases mixture pressure corresponded to the threshold of 'bottleneck effect.     

Light absorption in laser-heated cavities

The absorption of laser light in 0.25–1 mm diameter gold cavities, irradiated for the purpose of generating high-temperature blackbody radiation with intense laser radiation of either =0.44 m or =1.3 m wavelength, was investigated. For =0.44 m radiation the absorption exceeded 0.9 for all conditions, but dropped to only 0.3 for the smallest cavities irradiated at =1.3 m. Entrance hole and cavity filling with plasma seems important for the understanding of the observations.     

A free-electron laser pumped by the soliton laser

We propose a scheme for building a free-electron laser in the soft X-ray region pumped by the soliton laser. Making use of soliton laser wave evolution shape and single-pass small signal analysis, we find that this laser has two special advantages over the previous electromagnetic wave undulator free-electron lasers. One is a very small mass-shift effect because of the special characteristics of soliton laser; the other is that it has an additional frequency tuning effect based on the conventional free-electron laser's tunability. We also obtain the small signal gain and present some discussion.     

Radiation losses in completely ionized plasma

The losses caused by bremsstahlung during electron-ion and electron-electron collisions in a completely ionized plasma (in Born's approximation) are calculated. The calculation can be carried out analytically for a sufficiently dilute plasma (plasma with infinitely large Debay-Hückel radius). This assumption is satisfied very well by the known classification to actual controlled thermonuclear reaction. A dependence of the formI=an ². (1+3/2), wherea=0·73×10^–16 MeV.cm³.sec^–1,n is the number of ions per cm³ and =kT/mc ², is determined for the amount of energy radiated from 1 cm³ of plasma per sec. In the relativistic temperature regionkTmc ² the influence of electron-electron collisions begins to predominate. A number of important results concerning radiation losses in relativistic plasma will be published in a later paper.

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, ( ). ( -). . , I=an ². (1+3/2), =0,73. 10^–16 MeVcm²s^–1,n — =kT/mc ². kTmc ² . , .

     

Calculation of the force-dipole tensor for hydrogen in palladium and platinum

The force-dipole tensorP , also known as the elastic dipole and the double-force tensor, is calculated for hydrogen dissolved in palladium and platinum, using a microscopic model for the interaction potentials; the so-called effective medium theory. The force-dipole tensor describes the long range displacement field induced by hydrogen dissolved in the host metal lattice in the dilute limit. It can be related to the mean elastic hydrogen-hydrogen interaction energy and the critical temperatureT _c for the gas-liquid phase transition observed in systems such as PdH _x and NbH _x . Comparison show a fair agreement between theoretical and experimental values for the force-dipole tensor.     

Set theory and physics

Inasmuch as physical theories are formalizable, set theory provides a framework for theoretical physics. Four speculations about the relevance of set theoretical modeling for physics are presented: the role of transcendental set theory (i) in chaos theory, (ii) for paradoxical decompositions of solid three-dimensional objects, (iii) in the theory of effective computability (Church-Turing thesis) related to the possible solution of supertasks, and (iv) for weak solutions. Several approaches to set theory and their advantages and disadvatages for physical applications are discussed: Canlorian naive (i.e., nonaxiomatic) set theory, contructivism, and operationalism. In the author's opinion, an attitude of suspended attention (a term borrowed from psychoanalysis) seems most promising for progress. Physical and set theoretical entities must be operationalized wherever possible. At the same time, physicists should be open to bizarre or mindboggling new formalisms, which need not be operationalizable or testable at the lime of their creation, but which may successfully lead to novel fields of phenomenology and technology.     

Diode-pumped passively Q-switched Nd : YAG laser at 1123 nm

A diode-pumped Nd:YAG laser at 1123 nm is passively Q-switched by using a low doping concentration Cr⁴⁺:YAG crystal as a saturable absorber. When pumped by a 1.5-W laser diode, the laser produces pulses of 50-ns duration with a pulse energy of as much as 15 J and a peak power of 300 W at a pulse-repetition rate of 10 kHz. PACS 42.60.Gd; 42.55.Rz; 42.55.Xi     

On noise and fluctuations in a synchronously mode-locked cw laser system

A single-shot and synchronously-scanned streak camera, autocorrelation and noise spectrum analysing techniques are utilized to study the output characteristics of synchronously mode-locked cw lasers. Four main conclusions are drawn: (i) the pulse train from a synchronously-pumped dye laser reveals, besides phase jitter, considerable pulse shape fluctuations; (ii) autocorrelation measurements may be highly misleading when actual pulse shapes are considered; (iii) both the phase jitter and pulse shape fluctuations of the dye laser output are caused by the phase fluctuations of the pumping ion laser pulse train; (iv) the phase jitter of the ion laser proceeds from the fluctuations in the cavity roundtrip time with a characteristic time of about 5 s. Under optimum conditions the rms noise of the dye laser output was 2% and the phase jitter with respect to the rf sine drive of the acousto-optical mode-locker, 30 ps. A qualitative explanation fo the noise properties is given.     

Synthesis and spectroscopic studies of 4-Formyl-4′-N,N-dimethylamino-1,1′-biphenyl: The unusual red edge effect and efficient laser generation

The synthesis and photophysics of 4-formyl-4-N,N-dimethylamino-1,1-biphenyl are reported. The emission spectrum in various solvent polarities demonstrates solvatochromism, indicating that the fluorescence originates from an electronically excited species with a strong charge transfer character. The change in [ _max(absorption) – _max(emission)] varies from 1500 cm^–1 inn-heptane to as much as 7500 cm^–1 in acetonitrile. In protic solvents, the unusual excitation energy-dependent steady-state emission (red edge effect), resulting from solvent dielectric relaxation, was observed in media with a low viscosity. The large Stokes-shifted and high-yield fluorescence led to the observation of the efficient lasing action. The frequency tunability of the laser output is strongly solvent dependent, generating a new charge transfer laser dye in the blue-green region.     

Lasers without photons — or should it be lasers with too many photons?

Expanding the fields of a laser cavity in a set of orthonormal modes is a standard technique in laser theory. Expansion in a normal mode set is also the basis of the concept of photons. A substantial number of practical lasers do not, however, support any kind of normal or orthogonal cavity modes, and thus, their fields cannot be represented (at least not easily) in terms of normal modes, or photons. This leads to a number of unusual results, including situations in which the lowest-order mode of a cavity can contain substantially more energy than the total energy in the cavity, as well as enhanced quantum spontaneous emission far stronger than the single extra photon level characteristic of an ordinary laser oscillator. We review the theoretical origins of these unusual effects and present experimental confirmation of greatly enhanced Schawlow-Townes fluctuations in an unstable-resonator laser with a Petermann-noise enhancement factor of several hundred times.Dedicated to H. Walther on the occasion on his 60th birthday     

Regular and random output-power pulsations of a TEA CO2 laser with an intracavity nonlinear medium

The lasing dynamics of a pulsed atmospheric-pressure (TEA) CO₂ laser with a nonlinear medium (semiconductor InAs or InSb) inside the cavity is experimentally investigated. It is observed that introduction into the CO₂ cavity of nonlinear media having high nonlinear-absorption and a nonlinear refractive index leads, on the one hand, to a limitation of the emission intensity in the cavity and to an increase of the pulse duration (FWHM) from 0.1 sec to 2 sec, and on the other to appearance, on the output-power pulse envelope, of spikes having irregular amplitudes and durations, and separated by irregular intervals. It is established that the transition from the intermode-beat-induced regular pulsations to chaos has an emission-intensity threshold.Quantum Radiophysics Division, Lebedev Physics Institute. Translated from Preprint No. 136 of the Lebedev Physics Institute, Academy of Sciences of the USSR, 1989.     

The Optimum Operation of an Unified Mini-Optically Pumped NH3 Submillimeter Wave Laser

An unified miniature optically pumped NH₃ submillimeter wave laser (OPSMMWL), including a mini TEA-CO₂ pump laser, was developed. It lased successfully with coherent emission at 67.2m, 90.4m and 151.5m. The optimum operation of the unified mini-OPSMMWL was studied experimentally and the relations among SMMW laser output power, operating gas pressure, length and coupling condition of the cavity were measured. It has been found that buffer gas N₂ has significant effect on 67.2m and 151.5m emissions and very wide band SMMW laser emission was a common feature of the mini-OPSMMW cavity laser.     

Wide-range tunable sub-millimetre cyclotron resonance laser

The results of investigation of cyclotron type stimulated emission processes inp-Ge in strong crossedE B fields are presented. Using the optimumE,B field orientation the spectral range of continuous tuning of the emission line frequency was increased substantially. A tunable sub-millimetre laser with the tuning rangev = 25 to 95cm^–1 ( = 105 to 400m), output power 10 to 100mW and emission linewidthv 0.2cm^–1 is described.     

Quantum Theory of Self‐Phase Modulation of Ultrashort Light Pulses in a Medium with Inertial Electronic Nonlinearity

We develop a systematic quantum theory of formation of ultrashort light pulses in a squeezed state at selfphase modulation. The response time of the electronic Kerr nonlinearity of the medium is accounted for and the dispersion of linear properties of the medium is described in first approximation. The theory uses the approach based on the momentum operator for the electric field. The response function of the nonlinearity is contained in the interaction operator. The results obtained are valid when the pulse duration is far greater than the nonlinear response time and the carrier pulse frequency is offresonance. It is established that the instantaneous spectral distribution depends quasistatically on the pulse form. In the general case, the spectral distribution of the quadraturesqueezed component is defined by both the response time of the nonlinearity and the magnitude of the nonlinear phase addition. It is also shown that the frequency at which suppression of quantum fluctuations is greatest can be controlled by adjusting the phase of the initial coherent light pulse. It is found that, by registering the quadraturesqueezed pulse using a balanced homodyne detector, the squeezing effect can be efficiently measured if the timedependent phase of the heterodyne pulse obeys a specific dependence defined by the pulse form. The spectral photonnumber distribution of the quadraturesqueezed pulse is studied, and the photon antibunching effect is found for the photon number in a limited spectral band.     

The thickness dependence of the domain structure of magnetoplumbite

The changes in domain structure as a function of the thickness of the crystal are studied on artificial magnetoplumbite crystals. The thickness dependence of the width of the domains is also studied; up to thicknesses of about 10 it follows the theoretical halfpower law. Above 10 the exponent is 0·633. The energy density of the Bloch walls=4·82 erg cm^–2 and the exchange constantA=0·66×10^–6 erg cm^–1 are calculated on the basis of the above measurements.

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. , 10 . 0,633. = =4,82 erg m^–2 =0,66.10^–6 erg cm^–2.

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We thank Z. Málek and V. Janovec for discussions and some remarks.     

Uniaxial stress induced frequency shifts for muons in single crystal Fe

We report the first results on uniaxial stress-induced frequency shifts in an Fe single crystal. Stress was applied along the 100 axis, which was also the axis of magnetization induced by an external field. The observed frequency shift was –0.34±0.023 MHz per 100 microstrain, which corresponds to B/=+25.1±1.6 G/100. The positive sign arises from the negative sign of B itself. This result is interpreted as follows: The stress induces a statistical population shift between magnetically inequivalent sites. Extrapolations from the calculations of Sugimoto and Fukai from Nb and V to Fe yield order of magnitude agreement. The 4T(0) site system seems more likely.