Characteristics of a cw monolithic optical parametric oscillator

4 as a nonlinear crystal and obtained a pump threshold of 7 mW and an output power of 6 mW for a pump power of 40 mW. The OPO operated in a single longitudinal mode pair of a signal and an idler, over 1 h without mode hopping in the free-running condition. The signal and the idler wavelengths were tunable by 1 nm by changing the crystal temperature by 20 °C. The continuous tuning of the beat frequency between the signal and the idler was achieved by temperature tuning (slow control, 80 MHz/K) and E-field tuning (fast control, 0.75 MHz/V). We demonstrated the feasibility of frequency control by phase locking the beat frequency. The beat frequency could be successfully phase locked to a signal generated by a synthesizer through the electrooptic effect of the crystal. The phase locking could be maintained over 1 h. Received: 27 January 1998/Revised version: 9 March 1998     

Frequency measurement of130Te2 resonances near 467 nm

Precision spectroscopy on molecular tellurium is performed by measuring the frequency difference between the observed lines and an eigenfrequency of a high-finesse cavity mode. The mode frequency is derived from a measurement of the cavity's free spectral range taking into account the cavity dispersion due to phase shifts in the dielectric mirror coatings. The experimental technique is based on dual frequency modulation and is applied to determine the transition wavenumbers of several lines in¹³⁰Te₂ near 467 nm with an uncertainty of 2 × 10^–8.     

Improved resolution in VUV isochromat spectroscopy

The energy resolution of a VUV isochromat spectrometer employing the traditional energy selective Geiger counter can be significantly improved. The variance of the optical resolution function with the usual CaF₂ entrance window is (240 meV)². With SrF₂ we obtain (113 meV)² at room temperature and (73 meV)² at 70°C. A direct confirmation of these data, which were derived from a moment analysis of the threshold behaviour of an Au isochromat is provided by a measurement of image potential states at Cu(001).     

Observation of the first vibrations of the newly born Cs-CH CN complex

The femtosecond photodissociation of CsI in the CsI-CH₃CN complex has been studied. Recurrences are observed in the detection of the Cs⁺-CH₃CN ion complex. They are assigned to the first vibrations of the Cs-NCCH₃ bond formed after the CsI dissociation. This result is in good agreement with calculations on the similar NaI-CH₃CN system which predict a linear structure for the ground state complex. Received 27 October 1999     

Cationic Rydberg states observed in resonantly enhanced electron spectra of CS2

The inner valence electron spectrum of the CS₂ molecule has been investigated in the binding energy range between 18.6 and 26.3 eV using synchrotron radiation for ionisation. Photon energies in the range from 67 to about 167 eV have been used, with particular focus on 166.70, 166.89 and 167.09 eV for which S2p electrons are resonantly transferred into Rydberg orbitals close to the ionisation threshold. From there, autoionisation takes the molecule into various cationic states characterized by two valence holes and a Rydberg spectator electron. Many new bands are observed which contain vibrational progressions with spacings around 120 meV in most cases. These are assigned as excitations of the totally symmetric stretching ν₁ mode in the cationic state. The new bands reflect states in the cation that are close to the electronic states of the dication and assignments are made by comparison to double ionisation electron spectra.     

Probing Wave Packet Dynamics of I2- Anions with Pump--Probe Femtosecond Spectroscopy

The wave packet dynamics of I2^- anions is studied by using the time-dependent wave packet method. Two conclusions can be drawn from the calculations. First, the period of the total photoelectron signal oscillating with the propagation of delay time is about 750fs. Second, the photoionization of I2^- anions begin at the time 600 fs, and the time needed for the population of the electronic state of I2 neutral molecule to reach the maximum becomes shorter with the increasing delay time.     

Photodetachment of HF- in an Electric Field

Photdetachment of a negative HF^- ion in an electric field is studied by using the two-centre model and the closed orbit theory. An analytic formula is presented for the electron flux of HF^- in the presence of an electric field. The results show that the oscillation in the electron flux distribution is caused by the rescattering effect of the molecular ion core and the interference between the two nuclei. In addition, the interference between the orbits passing through the given spatial point also plays an important role in the electron flux distribution. This study provides a new understanding of the photodetachment of polar molecules in the presence of external field.     

Microwave Magnetic Properties of Nd2Fe17N3-δ with Planar Anisotropy

Microwave magnetic properties are studied for rhombohedral structure Nd2Fe17N3-δ with planar magnetic anisotropy. Its resin composites show the permeability μ＇0 = 4.15 at low frequency, the natural resonance frequency fT = 1.71 GHz and the resonance bandwidth 6.66 GHz. The calculated static permeability of Nd2Fe17N3-δ reaches 133. The microwave magnetic properties are determined by the c-axis anisotropy field, basal plane anisotropy field and high saturation magnetization. Based on microwave measurement and theoretical fitting on complex permeability spectra, Nd2Fe17N3-δ may be a promising microwave absorber with bandwidth wider than traditional hexaferrites materials in GHz ranges.     

Theoretical Investigation of Femtosecond-Resolved Photoelectron Spectrum of NaI Molecules

The time-resolved photoelectron spectra （TRPES） of NaI molecules are calculated by using the time-dependent wave packet method. Two different potential energy curves （adiabatic and diabatic） are adopted in the simulation. The third peak of the photoelectron spectra presented in the adiabatic calculation is induced by the reflection of the wave packet. The oscillating of the wave packet onto the diabatic energy curve is a decreasing process. The comparison of the photoelectron spectra between the two different calculations （adiabatic and diabatic） is presented.     

Preparation of nano-sized Al-substituted yttrium iron garnets by the mechanochemical method and investigation of their magnetic properties

The polycrystalline Y₃Fe_5−xAl_xO₁₂ compounds with x=0.5, 1.0, 1.5 and 2.0 were prepared by the mechanochemical method. The samples were milled for 40 h in a high-energy planetary mill and then calcined at different temperatures from 1300 to 1100 °C. The minimum calcination temperature to get a single phase garnet decreases by increasing Al concentration. X-ray diffraction patterns reveal that the structures of nano-powders are bcc and the garnet phase has been obtained after calcining. Also, the lattice constant of the samples decreases by increasing Al concentration ,which is discussed based on the substitution of smaller aluminum ions instead of iron ions. The average crystallite sizes are in the range 24-35 nm using Scherrer's formula. The Curie temperature of single phase samples was found to decrease by increasing Al concentration, which can be discussed upon the reduction of magnetic interactions per magnetic ion. When more Al³⁺ is added, the magnetization is reduced because of the reduction of superexchange interactions in crystal lattice.