Two photon ionization of alkali atoms

Two photon ionization cross-sections of the alkali atoms have been calculated by using Hartree-Fock-Slater wavefunctions and the results are compared with those obtained by Bebb using quantum defect method.     

Two photon magnetooptic effects

The theory of two photon magnetooptic effects such as polarization rotation and circular dichroism is developed. An effect which has not been previously discussed, the optical analog of the Hanle effect, is proposed.     

Triple ionization of lithium-like ions by photon impact

Within the framework of sudden approximation, the non-relativistic cross sections for the triple ionization of Li-like ions caused by absorption and Compton scattering of high-energy photons are calculated. The ratios of the triple-to-single and triple-to-double ionization cross sections are obtained. For neutral lithium atom, our predictions for σ3+/σ⁺ and σ3+/σ2+ are compared both with available experimental and theoretical results.     

Resonant two photon ionization of H and D atoms

H and D atoms have been ionized with tunable VUV + UV laser light by two-photon absorption, resonantly through the 2² P_{$\text{1}\text{2}$}, 2²P_{$\text{3}\text{2}$} fine structure doublet, with total energies very close to the ionization potential. Experiments have been carried out in the ionization chamber of a quadrupole massfilter, in a crossed atomic-laser beam configuration with sub- Doppler resolution of ～ 10 GHz. The sensitivity is ? 2.5 x 10⁵ atoms per cm³.     

Partitioning of the linear photon momentum in multiphoton ionization

The balance of the linear photon momentum in multiphoton ionization is studied experimentally. In the experiment argon and neon atoms are singly ionized by circularly polarized laser pulses with a wavelength of 800 and 1400 nm in the intensity range of 10(14)-10(15) W/cm2. The photoelectrons are measured using velocity map imaging. We find that the photoelectrons carry linear momentum corresponding to the photons absorbed above the field free ionization threshold. Our finding has implications for concurrent models of the generation of terahertz radiation in filaments.     

Two photon absorption spectrum ofp-dichlorobenzene

Two photon absorption spectrum ofp-dichlorobenzene has been studied in the spectral region 497–552 nm (one photon wavelength). Bands involving several frequencies of the excited electronic state not detected in the one photon absorption are seen. The observed two photon spectrum indicates that the electronic transition retains, to a large extent, the salient features of the two photon absorption spectrum of benzene and thus confirms chlorine as weak perturber (in the sense of Goodman and Rava [1]).     

Control scheme for two photon ionization of condensate atoms

The efficient photoionization of a Bose-Einstein condensate requires the creation of ions with the smallest possible transfer of atoms from the condensate into the thermal phase. The spontaneous decay from excited states into atomic states with momentum different from the initial one should be reduced. We investigate theoretically two-photon ionization of a rubidium condensate using near resonant excitation to the 6P state and second photon at 421 or 1002 nm into the continuum. Different ionization schemes with coherent control of the first excitation and reduction of the spontaneous decay are presented.     

Influence of light statistics on the many photon resonance ionization

We study the influence of laser temporal coherence on the width and shape of induced resonances in the many photon ionization.     

Two photon width of $\eta_c$

We discuss the measured partial width of the pseudoscalar charmonium state into two photons. Predictions from potential models are examined and compared with experimental values. On including radiative corrections, it is found that present measurements are compatible both with a QCD type potential and with a static Coulomb potential. The latter is then used to give an estimate on the decay into two photons. Results for are also compared with those from data through the NRQCD model. Received: 25 October 2001 / Revised version: 7 March 2002 Published online: 30 August 2002     

Inner-shell ionization of atoms by electron,positron and photon impacts

Plane wave Born approximation with Coulomb, relativistic and exchange corrections is employed to obtain L1-, L2- and L3-subshell ionization cross sections of several atoms due to electron and positron impacts for projectile energy varying from the threshold of ionization to 60 times the threshold energy. Photoionization cross sections for all the three L-subshells of the atoms are also calculated using the hydrogenic approximation for the atomic wave functions. For L3-subshell the present cross sections due to electron impact are in good agreement with a number of experimental data for different atoms over the entire energy range investigated. For L1- and L2-subshells the present calculations yield qualitative agreement with the experimental data. The agreement between the present results and the limited experimental data for positron impact is also satisfactory. The hydrogenic approximation for the L-subshell photoionization is found to be good at small photon energies but it underestimates the cross sections at large photon energies.     

Three photon ionization of alkali atoms at the ruby laser frequency

Three-photon ionization cross sections of alkali atoms for linearly and circularly polarized light have been calculated using the Green's function and the quantum defect methods. The results are compared with the values experimentally obtained by Cervenan et al.     

Cascade Two-photon Correlated-emission Optical Bistability

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Two photon absorption characteristics of bulk GaTe crystal

We have investigated the structural and optical properties of bulk GaTe crystal grown by vertical Bridgman method. Two photon absorption (TPA) properties of GaTe crystal have been investigated by the open aperture Z-scan technique under 1064 nm wavelength with 4 ns or 65 ps pulse durations. The TPA coefficients are greater in ns regime than that of ps regime. Upon increasing intensity of incident light from 5.02×10⁷ W/cm² to 1.07×10⁸ W/cm², the TPA coefficients increased from 3.47×10^?6 cm/W to 8.53×10^?6 cm/W for nanosecond excitation. Similarly, when intensity of incident light was increased from 6.81×10⁸ W/cm² to 9.94×10⁸ W/cm² the TPA coefficients increased from 3.53×10^?7 cm/W to 6.83×10^?7 cm/W for picosecond excitation. Measured TPA coefficient of GaTe crystal is larger than that of GaSe and GaS layered crystals.