Frequency measurements of saturated-fluorescence-stabilized CO2 laser lines: comparison with an OsO4-stabilized CO2 laser standard

4 frequency grid, to test the performance of the saturated fluorescence method for CO₂ laser frequency stabilization. The Allan variance for the saturated-fluorescence-stabilized CO₂ laser reached 60 Hz for an integration time of 300 s. We also performed three absolute measurements of CO₂ laser frequencies stabilized by the saturated fluorescence method, with a sub-kHz accuracy. We obtained a 1.7 kHz redshift of the CO₂ saturated fluorescence lines, which we attribute essentially to pressure. This is in contradiction with the previous observation of a blueshift [K.L. SooHoo, C. Freed, J.E. Thomas, H.A. Haus: Phys. Rev. Lett. 53, 1437 (1984)]. Furthermore, significant deviations of the measured frequencies from the data of Maki et al. [A.G. Maki, C.-C. Chou, K. Evenson, L.R. Zink, J.T. Shy: J. Mol. Spec. 167, 211 (1994)] demonstrate the need for a new calibration of the CO₂ frequency grid. Received: 1 December 1997     

Electronic and optical properties of Cd1-xZnxS nanocrystals

We report a numerical simulation of the conduction and valence band edges of Cd_1-xZn_xS nanocrystallites using a one — dimensional potential model. Electron — hole pairs are assumed to be confined in nanospheres of finite barrier heights. Optical absorption measurements are used to fit the bandgap of the Cd_1-xZn_xS nanocrystal material. A theoretical analysis is also made to calculate the energy location of bound excitons and the oscillator strength of interband transitions as a function of zinc composition. The aim of the latter study is to investigate the optical behavior of Cd_1-xZn_xS nanocrystals. An attempt to explain all the results is presented.     

Backward Wave Oscillator Based THz Spectroscopy, Diatomic Formalism and Optically Pumped Lasers

In this paper the Backward Wave Oscillator (BWO) based spectroscopy technique and its application to molecular spectroscopy especially to diatomic molecules have been discussed. This is a new and electronically controlled technique with enormous capabilities most of which are yet to be exploited. This paper also presents a part of the culmination of the collective efforts in developing a cohesive and consolidated enunciation of the spectroscopic parameters and their relationship to effective molecular Hamiltonians for diatomic formalism, linear four- atomic formalism & quasi-linearity, Watson Hamiltonian and the complexities in symmetric and asymmetric top spectral structures and its relationship to optical pumping and / or interstellar space. All these considered together present a beautiful and consistent picture of molecular spectroscopy and THz Electromagnetic sources.     

Investigation of polarisation effects in injection locked lasers

Received: 14 June 1996/Revised version: 6 November 1996     

Proton polarization in the p(e,e′p)π0 reaction and the measurement of quadrupole components in the N to Δ transition

The recoil proton polarization in the π⁰ production off the proton with longitudinally polarized electron beam has been studied as a means to measure quadrupole components in the N to Δ transition. On top of the Δ resonance a high sensitivity to a possible Coulomb quadrupole excitation is found in parallel kinematics. The ratio of S ₁₊/M ₁₊ multipole amplitudes can be determined from the ratio of the two in-scattering-plane recoil proton polarization components. Avoiding the absolute measurement of the polarizations, such a ratio allows small experimental uncertainties. Furthermore, the electron helicity independent proton polarization component enables the characterization of resonant and non-resonant pieces. Received: 3 November 1997     

Evidence for spontaneous interlayer phase coherence in a bilayer quantum Hall exciton condensate

Recent experimental work on the quantized Hall state at total filling factor ν_T=1 in bilayer 2D electron systems has revealed a number of striking phenomena, including a giant and sharply resonant enhancement of the interlayer tunneling conductance at zero bias. The tunneling enhancement is a compelling indicator of spontaneous interlayer phase coherence among the electrons in the system. Such phase coherence is perhaps the single most important attribute of the excitonic Bose condensate which describes this remarkable quantum Hall state.     

RF generator for compact CO2 waveguide lasers

This letter reports the fabrication and testing of a compact Radio Frequency Generator (Oscillator-Amplifier) for its integration in a CO₂ waveguide laser. The circuit uses a common source MOSFET transistor that has been modified for self-sustained oscillations impedance-matched to 50 Ω. RF power is supplied to the laser resonant cavity made of a ceramic-metal slab which is placed between a negative branch unstable optical resonator.     

The refractivity of CO2 gas in the region of 10 μm

The refractivity of the CO₂ gas is measured with an experimental error of 2% in the 10-m region, using 10.4-m band CO₂ laser line. The frequency of the CO₂ laser is swept through the Doppler profile of the laser line. The experiment is achieved using a 0.63-m He–Ne/10.6-m CO₂-laser interferometer with a 2-m long vacuum cell. From the result, it is found that the Koch's formula also holds for the wavelengths in the 10-m region within an accuracy of 2%.     

Self pulsing properties of optically pumped FIR NH3 lasers

We report on measurements of periodic and chaotic self-pulsing beyond the second threshold of far-infrared NH₃ lasers. While the instabilities of the 81 m¹⁴NH₃ laser follow a simple pattern, for the 374 m¹⁵NH₃ laser different pulsing properties are found in different parameter ranges.Pulses under conditions of high pumping power are measured in detail, in view of possible applications of these coherent, high-repetition rate far-infrared pulsed lasers.     

Condensation of 5-aminobenzimidazoles with β-ketoester

In the present work, we report the condensation of 5-aminobenzimidazoles with β-ketoesters leading to some new imidazo-[4,5-f]-quinoline derivatives. Based on the open chain intermediates obtention, the structure of the obtained imidazo-[4,5-f]-quinoline product has been discussed.