Use of the quartz crystal microbalance for kinetic studies of thermal decomposition of solids

A quartz crystal microbalance has been proposed for studies on the temperature dependence of the linear rate of a reaction interface advance in topochemical reactions of the thermal decomposition of solids. A quartz crystal microbalance has been used in investigations of the CuSO₄ · 5H₂O dehydration. The data agree fairly well with those available in the literature. Advantages and disadvantages of the method proposed are discussed.     

Dynamics of photoluminescence in GaInNAs saturable absorber mirrors

Femtosecond time-resolved photoluminescence experiments have been used to study the nonlinear dynamics of novel monolithic GaInNAs/GaAs semiconductor saturable absorber mirrors at 1.08 and 1.55 m. The mirror structures were grown using molecular-beam epitaxy followed by Ni-ion implantation and thermal annealing. We present photoluminescence measurements showing the critical role of post-growth processing on the response time of GaInNAs/GaAs absorber mirrors. PACS 42.65.Re; 42.50.Nn; 42.70.Nq     

Self-starting stretched-pulse fiber laser mode locked and stabilized with slow and fast semiconductor saturable absorbers

A self-starting stretched-pulse mode-locked erbium-doped fiber laser that uses fast and slow semiconductor saturable absorbers is described. By using two absorbers, we obtained reliable operation at a fundamental repetition rate with 250 pJ of pulse energy without multiple-pulse breakup. External chirp compensation was used to compress the highly chirped pulses to durations of 135 fs.     

A possibility to determine the value and sign of the nuclear quadrupole constant of the 184-KeV state of <Superscript>67</Superscript>Zn in ZnO by the induced βγ-direction correlation

It is shown that the value and sign of nuclear quadrupole constant of the 184-keV state of ⁶⁷Zn in ZnO can be determined using one of perturbed angular correlations of nuclear radiations: the induced βγ-direction correlation (⁶⁷Cu $ \underline {\beta ^ - } $ \underline {\beta ^ - } ⁶⁷Zn decay). The electric field gradient in ZnO crystal has been calculated by the full-potential linearized augmented plane wave method using the generalized gradient approximation of the exchange-correlation potential to interpret the result.     

Investigation of cw injection laser with external dispersive cavity

Tunable single-frequency lasing with output power up to 9 mW was achieved in an injection laser with an external dispersive cavity. The bistable lasing mode was investigated theoretically and experimentally. It is shown that its presence is due to the laser-diode active-region optical nonlinearity. Investigation of equal-frequency fluctuation spectra of the output power has shown that only modes with differing transverse structures can be excited simultaneously. Suppression of weak modes by the field of a strong mode was observed. This increases the stability of the single-frequency lasing as the laser output power is increased.Translated from Trudy Ordena Lenina Fizicheskogo Instituta im. P. N. Lebedeva, Vol. 141, pp. 62–88, 1983.     

Mode-locked semiconductor disk lasers with weakly saturated absorbers

The effect of absorber saturation on pulse shaping was studied both numerically and experimentally in a semiconductor disk laser. It was found that steady-state mode locking can be achieved even with very weak saturation of the absorber when the pulse energy is well below the saturation energy of absorption. The study discloses for the first time the direct impact of absorber modulation depth on the pulse width. Numerical analysis confirms that partial bleaching of absorption is adequate for formation of stable mode locking in SDLs. The fast gain dynamics of the semiconductor medium approach the dynamics of a slow gain medium at low pulse energies and high repetition rates with a pulse period much shorter than the gain recovery time. The presented results are of practical importance for multigigahertz repetition rate lasers, indicating that sufficient pulse shaping can occur when the saturable absorber is not fully bleached.     

Absorption Spectra of Metal Atoms Adsorbed on the Surface of a Single Crystal

A method for obtaining the spectra of atoms adsorbed on a single crystal with an ion-covalent bond is suggested. A photostimulated burst of luminescence is used to record the spectra. The atoms are deposited in a vacuum by a mass-spectrometric technique. The absorption spectrum of silver atoms adsorbed on a silver chloride single crystal at concentrations comprising a millionth fraction of the surface monolayer has been obtained. It has been revealed that the optical ionization potential of an adsorbed silver atom is equal to 1.9 eV.     

Comparative study of single-crystal dehydration of LiCOOH.H2O and Li2SO4·H2O

The kinetics of isothermal dehydration of two crystal hydrates with equivalent water molecule sublattices (LiCOOH.H₂O and LiSO₄.H₂O) was investigated in vacuum with a quartz crystal microbalance, and the dynamics of structural reorganization of the substances was studied by the synchrotron radiation method. Differences were found both in the nucleation stage and in the stage of reaction interface advance. The results indicate that the kinetic behaviour of isothermal decomposition of solids is determined by the structural reorganization of a metastable intermediate.

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Zusammenfassung Die Kinetik der isothermen Entwässerung zweier Kristallhydrate mit gleichartigen Teilgittern der Wassermoleküle wurde untersucht mittels isothermer TG im Vakuum und Synchrotron-Röntgenbeugung. Unterschiede zwischen beiden Materialien werden sowohl in der Keimbildungswie- wei in der Ausbreitungsphase gefunden. Die Ergebnisse zeigen, dass die Kinetik der isothermen Zersetzung fester Stoffe durch die strukturelle Reorganisation eines metastabilen Zwischenprodukts bestimmt wird.

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HCOOLi.H₂O Li₂SO₄.H₂O . , — . , . , .

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The authors would like to thank N. Kosova for experimental assistance.     

On the applicability of the first-order equation for the reactions of solids

It is suggested that besides its traditional application to describe random nucleation, the first-order equation F1 can be used for the diffusion kinetics of gas-solid small particles reactions.

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, F1 - - .