Recent developments in X-UV optics and X-UV diagnostics

Metrology of XUV beams (X-ray lasers, high-harmonic generation and VUV free-electron lasers) is of crucial importance for the development of applications. We have thus developed several new optical systems enabling us to measure the optical properties of XUV beams. By use of a Michelson interferometer working as a Fourier-transform spectrometer, the line shapes of different X-ray lasers have been measured with a very high accuracy (/10^-6). Achievement of the first XUV wavefront sensor has enabled us to measure the beam quality of laser-pumped as well as discharge-pumped X-ray lasers. A capillary discharge X-ray laser has demonstrated a very good wavefront allowing us to achieve an intensity as high as 3×10¹⁴ Wcm^-2 by focusing with a f=5 cm mirror. The sensor accuracy has been measured using a calibrated spherical wave generated by diffraction. The accuracy has been estimated to be as good as /120 at 13 nm. Commercial developments are underway. At Laboratoire dOptique Appliquée, we are setting up a new beamline based on high-harmonic generation in order to start the femtosecond, coherent XUV optic . PACS 07.85.Nc;32.70.Jz;41.50.+h;42.15.Dp;42.55.Vc;52.70.La     

Замечание К теории по степенного возникновения подви жных слоев в плазме инертных газов

[1] t _B , t _B . , t _B , . .

---

A note on the theory of the successive production of moving striations in the plasma of inert gases

Approximate expressions are derived on the basis of Pekárek's theoretical paper [1] for the period of the maximum t_B of a wave packet produced by the passage of a wave of stratification before the aperture of a photomultiplier, and for its time width in the half-height t_B. The relaxation time of a wave of stratification, following from the theory [1], can thus be calculated by means of the experimentally measured velocity of motion of the maximum of a wave packet u and its width t_B. The calculation is supplemented by numerical data on the magnitude of errors committed by using approximate expressions.

     

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.

---

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

     

Pulse shortening to 25 ps in a cw mode-locked Nd: YAG laser by introducing an intracavity etalon

The gain spectrumG(v) of a cw mode-locked Nd:YAG laser is flattened by a properly designed intracavity etalon. The increase in amplification bandwidth allows the generation of very stable trains of pulses shorter than that of standard systems. A reduction of the pulse width from 70 to 25 ps is observed by incorporating a BK 7 platelet of 420 m thickness in the resonator. The properties of the laser are investigated as a function of the thickness and the orientation angle of the etalon. The laser performance is found to be considerably influenced by the fact that the Nd³⁺ laser transition at 1.064 m consists of a line doublet.     

Polarization switching in a ring cavity with resonantly drivenJ=1/2 toJ=1/2 atoms

We have solved within the mean field limit for the steady state behaviour of a gas ofJ=1/2 toJ=1/2 model atoms in a ring cavity excited by an incident laser field of arbitrary polarization. Results are presented for the case of zero applied magnetic field and exact resonance between the laser frequency, the atomic transition and a cavity resonance (pure absorptive case). We find that the behaviour of the polarization switching between ⁺ and ^– outputs depends on the values of the upper and lower state collisional relaxation rates, expressed via a single parameter . The case of linearly polarized input is of particular interest since optical bistability is found to occur for 2, being pre-empted by polarization switching for >2. The results are discussed in terms of an atomic feedback mechanism coupling the ⁺ and ^– modes.     

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.     

Gas kinetic studies using a table-top set-up with electron beam excitation: quenching of molecular nitrogen emission by water vapour

A table-top set-up for studying gas kinetic processes in dense gases via time resolved optical spectroscopy is presented. The set-up uses low energy electron beams for gas excitation. A thin silicon nitride membrane separating the electron source and the gas cell allows to use electron energies as low as 10–15 keV. The electron source is operated in a fast pulsing mode with a pulse width of 5 ns and repetition rates up to 30 kHz. Light emission from the target gas sample is studied and time resolved photon counting is used to measure decay times and collisional rate constants for specific excited states. The experimental concept is applied to measure the rate constants for quenching of molecular nitrogen in the C 3u state (vibrational levels 0 and 1) by water vapour. Quenching rate constants of (7.1 ±0.7)×10-10 s-1 cm3 and (6.7 ±0.7)×10-10 s-1cm3 were obtained for the C 3u (v = 0) and C 3u (v = 1) vibrational levels, respectively.     

The phonon spectrum of high energy heat pulses generated in thin metal films

The phonon spectrum of high energy heat pulses (10⁴W/cm²) generated by current pulses in thin evaporated metal films was studied in ruby by time resolved optical spectroscopy. The experiments show that the population temperature of the phonon states rises with rising phonon energies in accordance with theoretical predictions of Perrin and Budd [1, 2]. The thermalization of the phonon spectrum needs a time of approximately 900 µs in ruby flushed with cold helium gas.This work was supported by the Deutsche Forschungsgemeinschaft, SFB65     

The second-order effects in the “rotating disk” experiment

We find the second-order inv/c effects in the four different modifications of the rotating disk experiment whose first-order effects have been analyzed and the experimental results obtained by us reported in another paper. The differences between our absolute space-time theory and the Newtonian ether theory are within effects of second order inv/c. We propose experiments for the measurement of the second-order effects on the rotating disk that can be considered asexperimenta crucis between both theories.     

Enhancement of activated decay of metastable states by resonant pumping

We consider the effect of a high-frequency pumping cost on the escape rate of a classical underdamped Brownian particle out of a deep potential well. The energy dependence of the oscillation frequency(E) is assumed to be weak on the scale of thermal energy,_E(0)T(0)T/V₀ (0)[_E(0) is the derivative of(E) atE= 0,V ₀ is the barrier height,V ₀ T]. The quadratic-in- contribution to the decay rate is calculated in two different regimes: (1) for the case of resonance of the pumping frequency with the nth harmonic of the internal motion at an energye, when = n(e); (2) for a rollout region of the basic resonance near the bottom of the potential well, when ¦-(0)¦ and is the damping coefficient. In the latter case the absorption spectrum and the enhancement of the decay rate are calculated as functions of two reduced parameters, the anharmonicity of the potential,v _E (0)T/, and the resonance mismatch, [ —(0)]/. It is shown that the effect of the pumping increases with diminishing ¦v¦ and at small v is proportional tov ^–1. In this regime, the dependence on is stepwise: the pumping contribution is large for v > 0 and small for v < 0. In the frame of our theory, the decay rate is invariant against the simultaneous alternation of the signs of andv. The spectrum of the energy absorption has the standard Lorentzian shape in the absence of anharmonicity,v=0, and with increasing of ¦v¦ shifts and widens retaining its bell-shape form.     

Temporal confinement of the harmonic emission through polarization gating

We show experimentally that a simple optical setup is able to reduce the duration of the harmonic emission generated by long (many optical cycles) laser pulses. By controlling the time-dependent ellipticity during the laser pulse, one can confine the harmonic emission to a narrow temporal window where the polarization is quasi-linear. The results obtained and their comparison with a simple model show a shortening of a factor 2 for harmonics located in the plateau region. Using shorter laser pulses of 15-20 fs duration should make it possible to isolate a single attosecond pulse.Received: 25 November 2002, Published online: 8 July 2003PACS: 42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation - 32.80.Wr Other multiphoton processes     

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     

High-power source of coherent picosecond light pulses tunable from 0.41 to 12.9 μm

We report a high-power source of coherent picosecond light pulses based on optical parametric generation and amplification in LiB₃O₅ and AgGaS₂ crystals. The spectral range of this continuously tunable source covers the visible, near-infrared and medium-infrared spectrum from 0.41 to 12.9 m. An optical parametric generator and amplifier, consisting of two type-I phase-matched LiB₃O₅ crystals and a diffraction grating, is pumped by the third harmonic of a picosecond Nd:YAG laser and provides spectrally narrow, high-power pulses from 0.41 to 2.4 m. Energy conversion efficiencies up to 16 percent are achieved. The pulse duration is about 14 ps, the bandwidth between 10 and 30 cm^–1. The tuning range is extended to 12.9 m by mixing the infrared output between 1.16 and 2.13 m with the fundamental of the Nd:YAG laser in type-I-phase-matched AgGaS₂ crystals. Up to 25 percent of the pulse energy at 1.064 m is converted into parametric infrared pulses. Bandwidths between 3 and 8 cm^–1 and a pulse duration of approximately 19 ps are measured for these pulses. We also observe a retracing behaviour in the tuning curve of AgGaS₂ not reported before.     

Generation of 320 fs pulses with a distributed feedback dye laser

A new achromatic distributed feedback dye laser (DFDL) arrangement is described. The experimental conditions for subpicosecond pulse generation with the new device were investigated. For the first time, stable generation of subpicosecond pulses (350 fs) at 616 nm was achieved with a DFDL. The simultaneous spectral and autocorrelation measurements showed that the amplified DFDL pulses are nearly transform limited, having a pulse form close to the sech² shape.     

ПОГЛОЩЕНИЕ И РАССЕЯНИЕ МОНОКРИСТАЛЛОВ NaCl ∶ Ni

NaCl Cd [10]. , NaCl Ni , .

---

Absorption and dispersion on NaCl Ni crystals

The results of measuring the absorption and dispersion of light on NaCl Cd crystals were compared with the X-ray diffraction measurements by Toman [10]. The comparison showed that under certain conditions micro-regions of segregated impurities are produced in NaCl Ni crystals, apparent in an increased dispersion of light in the ultra-violet region.

     

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.     

ИЗОТОПЫ ФТОРА F19 И F21 В МОДЕЛИ НИЛЬССОНА

Energy levels and electromagnetic properties of fluorin isotopes in the Nilsson's model with Coriolis mixing are investigated. Position of the F¹⁹ levels is satisfactorily explained up to the energy of 4·5 MeV. Concerning the F²¹ it seems that the shell model will better correspond to the F²¹ nucleus.

---

---

. , .     

Dark body and black hole horizons

The formula for the horizon of a Newtonian dark body is given and compared to that of a relativistic black hole: a Newtonian dark body has at least one hair.     

Intersubjectivity,relativistic covariance,and conditionals: response to C. I. J. M. Stuart

A misunderstanding persists between Stuart and me, which I do my best to clarify. Bayesian inverse subjectivities versus relativistic covariance and physical intersubjectivity are discussed. A joint number of chances formalism taking care of the propagation of the probability of causes is proposed.     

Contribution to the theory of single-mode laser modulation II. Conduction modulation

The problem of conduction modulation of laser radiation is considered. It is shown that acoustic wave interacting with photon field in active medium causes a periodic modulation of the number of quanta in the single-mode gas laser. The problem of modulation is solved quantum mechanically and it is shown that dielectric and conduction modulation give similar results.