Ivan L. Stefanov

Ion-implanted polymethyl methacrylate beam splitter/coupler for 1.55 μm applications

The applicability of layers of ion-implanted polymethyl methacrylate (PMMA) for beam splitting of laser light at the telecommunications wavelength of 1.55 mum is examined. Bulk PMMA is studied, subjected to low-energy (50 keV) silicon ion implantation at various ion fluences in the range from 10(14) to 10(17) cm(-2). The formed ultrathin near-surface ion-implanted layer of a thickness of about 100 nm, buried in a depth of approximately 100 nm, can be used to split (or combine) laser beams at 1.55 microm with a low absorption loss.

Interference effects between raman and parametric stimulated emission

The interaction between stimulated electronic Raman scattering and four wave parametric emission in potassium has been studied on the basis of common real states and emission channels. The modified intensity Stokes dependence and higher saturation pump intensity have been accounted for by the model developed. Two tunable pump waves are used to initiate the two steps, involving a dipole forbidden 4S − 3D transition.

Four-wave mixing in potassium involving quadrupole excitation and emission

The stimulated 331.1-nm emission in the K(5D → 4S) quadrupole transition has been studied after excitation by two tunable dye laser waves, one of which is in the K(4S → 3D) quadrupole transition. A four-wave mixing mechanism has been shown to be responsible for the UV emission based on intensity, temperature, and spectral measurements. The measured conversion efficiency is compared with the calculated value.

Efficient red stimulated emission enhanced by quadrupole Raman scattering

Abstract An efficient 6S-4P and 4D-4P stimulated emission in K is reported in a two-step process, involving dipole forbidden stimulated electronic Raman scattering. The Raman gain has been used to measure the quadrupole matrix element μ 4S,3D =5.1 X 10 -4 au.

Laser-induced thermo-lens in ion-implanted optically-transparent polymer

A strong laser-induced thermo-lens (LITL) effect is found in optically-transparent ion-implanted polymer upon irradiation by a cw laser with a power up to 100 mW (λ = 532 nm). The effect is observed in bulk polymethylmethacrylate (PMMA) implanted with silicon ions (Si+). A series of PMMA specimens is examined, subjected to low-energy (50 keV) Si+ implantation at various dosages in the range from 1014 to 1017 ions/cm2. The thermo-lensing is unambiguously attributed to the modification of the subsurface region of the polymer upon the ion implantation. Having a gradient refractive-index in-depth profile, the subsurface organic-carbonaceous layer produced in the polymer by ion implantation, is responsible for the LITL effect observed in reflection geometry. The LITL occurs due to optical absorption of the ion-implanted layer of a thickness of about 100 nm buried in a depth ~ 100 nm, and subsequent laser-induced change in the refractive index of the Si+-implanted PMMA. Being of importance as considering photonic applications of ion-implanted optically-transparent polymers, the LITL effect in Si+-implanted PMMA is studied as a function of the implant dose, the incident laser power and incidence angle, and is linked to the structure formed in this ion-implanted plastic.

Stimulated emission by hybrid transitions via a heteronuclear molecule

Abstract A stimulated red emission is studied by hybrid transitions involving the NaK heteronuclear molecule. The excitation channels in NaK and K are identified and the mechanisms of the stimulated emission are discussed.

K(6S-4P) parametric emission excited by bound-bound transitions of NaK

The authors have studied extensively the stimulated emission at 691.1 nm and 693.9 nm identified as 6S-4P1/2, 3/2 transitions in potassium. The origin of the emission is thought to be four-wave parametric emission induced by hybrid transitions. The stimulated emission is enhanced by cascading transitions, the presence of nearby atomic states, stimulated electronic Raman scattering and molecular background signal. Excitation, absorption and emission measurements indicate that bound-bound NaK(X-B) transitions play a dominant role. The rate of energy transfer NaK to K is evaluated as kET approximately=2.3*10-9 cm3s-1.

The luminescence response of Eu(III)-thenoyltrifluoroacetonate complexes upon preresonant excitation with femtosecond laser pulses.

The luminescence of thenoyltrifluoroacetonate (TTA) coordination complexes of trivalent europium ion (Eu(III)) in aqueous solutions and in solid-state polymeric films is probed upon single- and two-photon preresonant excitation with Ti:sapphire femtosecond laser. Particularly, diamine-liganded Eu(III)(TTA)(3) and poly(oxyethylene phosphate)tris(beta-diketonate)Eu(III) complexes are examined aiming their possible applications as luminescent labels for sensing and imaging of biological molecules. Even at a pre-resonance, the excitation of these compounds with high-intensity, broadband light of frequency-doubled Ti:sapphire femtosecond laser centered around 400 nm results in a luminescence response suitable for fluorometric applications.

Observation of forbidden five-wave mixing in potassium vapor

Abstract A coherent emission corresponding to the K(6P-4S) transition at 344 nm has been observed under two-wavelength excitation of potassium atomic vapor. The nonlinear origin of the signal is confirmed by divergence, forward-to-backward and temporal measurements. The analysis shows that a five-wave mixing process is responsible, involving additional Stokes waves, generated in the medium.

Optical six-wave mixing via two forbidden transitions in the potassium atom

Optical six-wave mixing via two forbidden transitions has been studied in the potassium atom by resonant interaction with two tunable dye lasers. Despite the two quadrupole resonances, one in excitation and one in emission, the non-linear optical susceptibility responsible is significantly enhanced. Comparison is made with other forbidden non-linear schemes, realized by the same two-wavelength resonant excitation.