Theory of two-photon lasers II

In order to treat two-photon laser action including noise close to threshold the Fokker-Planck equation is used and its steady state solution determined. It allows us to discuss the stable, unstable, and metastable states of the two-photon laser.     

Theory of two-photon lasers III

We treat the semiclassical equations and the Fokker-Planck equation of a two-photon laser with one or two injected signals and treat both the degenerate and nondegenerate case. The resulting behaviour in the two-photon laser is discussed by means of potential functions which allows one to determine the stable, unstable, and metastable states.     

Generalized coherent states and the statistics of two-photon lasers

Stimulated two-photon emission is proposed as a possible mechanism for the generation of “generalized coherent states”, which have useful quantum properties not available in ordinary coherent states.     

Theory of coherent two-photon absorption

An exact solution for the propagation of two ultrashort pulses through a two-photon near resonant absorbing medium is obtained under the condition that the initial number of photons/s cm² in the two pulses are the same. High-power pulses develop sharp peaks as they propagate through the medium.     

Theory of multiple-pass two-photon Doppler-free spectroscopy

Electron stimulated desorption (ESD) of CO on Ru (001) leads to emission of CO⁺ and O⁺ ions from the same adsorption states. Following earlier work on this system, a correlated study of its ESD behaviour together with LEED, Δϕ, and TPD measurments has been carried out. The filling of the two states found earlier can be seen in ESD also. The dividing line between the high and low energy states is different in room temperature adsorption on the one hand, and desorption or equilibrium measurements at elevated temperatures on the other, which is explained by incomplete attainment of equilibrium in the layer under the first condition. The behaviour of the ESD ion currents with coverage showstthat part of the molecules occupying high energy sites in the ordered layer of intermediate coverage are shifted to less favourable sites at higher coverage, so that the full layer consists of a mixture of states due to the occupation of different sites in the compressed layer, possibly accompanied by lateral interactions. ESD also suggests that the high energy sites are the on-top sites rather than the threefold sites.     

A comparison between degenerate paramagnetic oscillators and two-photon correlated-spontaneous-emission lasers

The degenerate parametric oscillator (DPO) is analyzed with the nonlinear material treated quantum mechanically. The source of squeezing in the DPO is the same as in the two-photon correlated-spontaneous-emission laser (CEL) — the level coherence. In this sense, they are similar. The amount of squeezing in DPO is the same as in the two-photon CEL at two-photon resonance, but the gain in DPO is usually much smaller than that in the two-photon CEL at two-photon resonance.     

强激光场下的双光子自电离理论

本文研究了包括二阶离化过程的强激光场下的双光子自电离。导出了光电子谱的解析表达式,并对一些特殊情况下的光电子谱进行了分析。     

Theory of lasers using free-free transitions

An equation is derived that gives the evolution in the radiation intensity of a laser using free-free transitions in the case of scattering of a relativistic beam of electrons by a spatially periodic magnetic field. The first two perturbation orders are considered. Expressions are obtained for the linear gain and the saturation coefficient. The results are analyzed numerically.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 79–84, August, 1980.     

Theory of synchronously pumped dye lasers

An analysis of cw synchronously pumped dye lasers is presented. Under the assumption that the cavity (tuning element) bandwidth is much wider than the bandwidth of the transform limited pulses generated, the pulse forming dynamics is rigorously treated. It is shown that for a finite mismatch between the lengths of the dye and the pump lasers, a steady-state pulse develops in the dye laser cavity with a conserved pulseshape. The characteristics (energy, shape, peak power, duration) of these pulses of ultimate width are quantitatively determined as a function of cavity mismatch. An analytical solution for the pulse envelope is determined, which yieldsI(t)∝Sech²(t/t _p ) to a good approximation.     

Theory of transient two-photon resonant up-conversion with non-synchronized excitation

The theory of the two-photon resonant up-conversion process (ω_a + ω_a) + ω_c ? ω_d is developed for short pulse excitation. Prominence is given to the case where the pulse at frequency ω_c is not time-synchronized with the pulse ω_a but travels immediately behind it. Not only is the conversion efficiency thereby maximized, but the associated theoretical simplification enables several analytical formulae to be derived which provide new insight into the mechanism of resonant non- linear interactions. In particular, an expression is derived for the maximum useful energy per unit area of the pulse at ω_c. Exceeding this value is of little or no advantage in the non-synchronized case and is positively detrimental when the a- and c-pulses are coincident. The results are supported by computer solutions.     

Theory of coherent,degenerate two-photon absorption and emission

The theory of the coherent, two-photon resonant interaction of a monochromatic field with N atoms is given. It is seen that the dynamics of the atom-field system can be completely determined when the field is “strong”. Two specific examples are given: (i) two-photon absorption by atoms in ground state, and (ii) stimulated two-photon emission by fully excited atoms, assuming a coherent field in both cases. In case (ii), the field shows photon-antibunching after the decay of half of the atoms. The merits of our approach are shown by comparing with other treatments. Our results can also be applied to certain degenerate four-wave mixing processes which are described by a similar Hamiltonian.     

Theory of passively mode-locked cw dye lasers

The circulation of an ultrashort light pulse in a continuously pumped modelocked dye laser with a linear cavity configuration containing the active dye, the saturable absorber and a bandwidth-limiting elements is treated. The steady-state condition that the pulse shape reproduces after each cavity round-trip leads to a nonlinear integro-differential equation for this pulse shape. An approximate method for the solution of this equation not limited to the case of low laser gain and small pulse energies is given. The stable single pulse region and characteristic pulse parameters, as energy, duration, intensity and asymmetry, are considered in dependence on the laser parameters.