D. Ohlmann

Reverse saturable absorption in C60-doped porous glasses studied by single- and double-pulse pump–probe experiments

We investigate the nonlinear absorption of C60-doped porous sol-gel glasses by single- and double-pulse pump–probe experiments. We find that the reverse saturable absorption (RSA) of these samples can be explained in the frame of a five level system as it is commonly used for C60 solutions. We observe a strong saturation of the RSA at high fluences, especially if the molecules are prepared in the triplet state. In a double-pulse pump–probe experiment we measure the triplet quantum yield for C60 solutions (0.8) and doped glasses (0.25) and the singlet and triplet absorption cross sections. In the first excited singlet state (S1) lifetimes of 1 ns and 65 ps are determined in solutions and glasses, respectively. We find that the dynamics of both depopulation processes, direct S1–S0 relaxation, and intersystem crossing is faster in glasses than in the case where C60 is in solution in a liquid aromatic solvent. We tentatively explain these findings by the absence of a stabilizing solvent and a perturbation of ...

Linear and nonlinear optical properties of ZnCdTe monocrystals

Abstract The linear optical properties of Zn 0.87 Cd 0.13 Te are characterized at liquid helium and at room temperatures. When an electron-hole plasma is created by a strong light pump pulse, important optical nonlinearities show up at room temperature in “pump and test” measurements. They lead to an induced absorption and to pulse deflection, which are determined separately. We find for the real Δ n ′ eh and imaginary Δ n ″ eh parts of the nonlinear index of refraction per electron-hole pair Δ n ′ eh = -4.4 × 10 -19 cm 3 and Δ n ″ eh = 2.2 × 10 -21 cm 3 , respectively. The dynamics of both nonlinear effects is studied as a function of the time delay between the pump and test pulses and a decay time of 9 ns is found, which is attributed to the lifetime of the plasma.

Preparation of Optical Quality ZnCdTe Thin Films by Vacuum Evaporation.

A procedure to make optical quality thin films of Zn(x)Cd(1-x)Te by use ofvacuum evaporation of the ternary compound has been developed. Thestarting point was the preparation of the compound that was then usedas the source in a simple vacuum evaporation system. Thecharacteristics of a film containing 85% ZnTe (x =0.85) are presented. Electron microscope, atomic forcemicroscope, x-ray and optical spectral measurements were made. Theindex of refraction was determined at room temperature fromtransmittance measurements in the range of from 580 to 800 nm and wasfound to agree within 1% with values found by others for singlecrystals. We did this by assuming a Sellmeier equation and a knownindex of refraction at infinite wavelength. The calculation alsoyielded the roughness of the film.

Tunable optical nonlinearities in Cd1−xZnxTe ternary alloys

Bulk Cd1−xZnxTe ternary compounds are studied through nonlinear optical pump and probe experiments for different zinc concentrations x. These measurements, similar to excitation spectra, enable us to determine the frequency dependence of the optical nonlinearity. It is attributed to the presence of impurity levels in the material. The two-photon absorption through these states gives rise to a high induced absorption.

Structural and Optical Properties of Cd1—xZnxTe Epilayers Grown on GaAs (001) by Pulsed Laser Deposition

Epilayers of Cd 1-x Zn x Te on GaAs (001) substrates were grown by a pulsed laser deposition technique, using either polycrystalline or cold-pressed targets. The composition and structural quality of these epilayers were investigated by energy dispersive X-ray analysis, and X-ray diffraction. A large and widely tunable induced optical absorption has been observed in these CZT epilayers.

Optical nonlinearities of ZnCdTe at room temperature

Abstract We have observed unusually strong optical nonlinearities in Zn0.87Cd0.13Te at room temperature. By measuring the time-resolved spatial deflection of a test pulse when the sample is inhomogeneously excited by a pump pulse, absorptive and dispersive nonlinear contributions can be separated and the lifetime of the electron-hole plasma determined. These important index changes associated with low linear absorptions can be used to perform optical logic gates or other opto-electronic devices of very high contrast and with a nanosecond response time.

Dynamics of beam defocusing and induced absorption in CdZnTe alloys

We study the optical nonlinear properties of bulk Cd0.13Zn0.87Te monocrystals at room temperature near the band gap. In time‐resolved test and pump experiments, they manifest themselves by a defocalization and an induced absorption of the test beam in the presence of the pump beam. By measuring the spatial intensity profile of the test pulse transmitted through the sample, we determine the real and the imaginary parts of the refractive index as functions of the photon energy and time delay between pump and test pulses.

Optical nonlinear properties of Cd1−xZnxTe epilayers grown on (100) GaAs by pulsed laser deposition

Abstract This paper reports induced absorption in Cd 1− x Zn x Te thin films epitaxially grown by pulsed laser deposition on (100)-oriented GaAs substrate. The high optical nonlinearity is adjustable in the visible over a wide spectral region as the concentration x is varied.

Adjustable optical nonlinearities in Cd1−xZnxTe alloys

Abstract This paper reports observed induced absorption in bulk Cd 1− x Zn x Te compounds in pump and probe experiments. The results are compared to the numerical simulation of a three-level system. The high nonlinearities, attributed to impurity levels in Cd 1− x Zn x Te, are tunable over a wide spectral region.

Dynamics of optical nonlinearities in CdZnTe at room temperature

Abstract Bulk Cd 0.13 Zn 0.87 Te monocrystals are studied by nonlinear optical experiments at room temperature near their absorption edge. Time-resolved test and pump experiments allow us to determine separately the refractive index and absorption changes induced by the pump pulse by measuring the spatial intensity distribution of the test pulse.