E. Steveler

Direct and indirect excitation of Nd3+ ions sensitized by Si nanocrystals embedded in a SiO2 thin film

The luminescence properties of Nd-doped SiOx layers containing silicon nanocrystals (Si-ncs) were investigated by steady state, time-dependent and power-dependent photoluminescence spectrometry and photoluminescence excitation experiments. Both direct and indirect excitation processes of Nd3+ ions have been evidenced. The energy transfer mechanism between Si-ncs and Nd3+ ions is favored by the overlap between the emission spectrum of confined excitons in Si-ncs and the Nd3+ absorption from the ground state to 4F5/2 electronic level. The more intense Nd-related emission was obtained in samples containing 0.5 at. % of Nd and characterized by an indirect excitation cross section equal to 8 × 10−15 cm2.

Optical index measurement of InAs/GaSb type-II superlattice for mid-infrared photodetection at cryogenic temperatures

The complex optical index n (=n + i κ) of InAs/GaSb type-II superlattice (T2SL) was determined in the 1–6 μm range from reflectivity measurements of resonant structures at 80 K. Several air/superlattice/gold cavities of various thicknesses were fabricated and their reflectivity was measured. As the large variations induced by the cavity resonances in the studied range can be accurately modeled, we were able to determine the complex optical index n of InAs/GaSb T2SL with an error of only a few percent. We found that the in-plane refractive index n of the T2SL lies between 3.65 and 3.77 in the mid-infrared wavelength range, and the absorption coefficient κ decreases from 0.23 to 0.001 as the wavelength increases from 1.25 to 5.65 μm. The subtractive Kramers-Kronig relation allowed us to verify our determination of n.

Resonant metallic nanostructure for enhanced two-photon absorption in a thin GaAs p-i-n diode

Degenerate two-photon absorption (TPA) is investigated in a 186 nm thick gallium arsenide (GaAs) p-i-n diode embedded in a resonant metallic nanostructure. The full device consists in the GaAs layer, a gold subwavelength grating on the illuminated side, and a gold mirror on the opposite side. For TM-polarized light, the structure exhibits a resonance close to 1.47 μm, with a confined electric field in the intrinsic region, far from the metallic interfaces. A 109 times increase in photocurrent compared to a non-resonant device is obtained experimentally, while numerical simulations suggest that both gain in TPA-photocurrent and angular dependence can be further improved. For optimized grating parameters, a maximum gain of 241 is demonstrated numerically and over incidence angle range of (−30°; +30°).

Indirect excitation of Er3+ ions in silicon nitride films prepared by reactive evaporation

Er-doped silicon nitride films were obtained by reactive evaporation of silicon under a flow of nitrogen ions and were annealed at temperatures up to 1300 °C. Samples were studied by infrared absorption and Raman spectrometries and by transmission electron microscopy. The 1.54 μm Er-related photoluminescence (PL) was studied in relation with the structure with pump excitation at 488 and 325 nm. Steady-state PL, PL excitation spectroscopy, and time-resolved PL were performed. The results demonstrate that Er3+ ions are indirectly excited both via silicon nanocrystals and via localized states in the silicon nitride matrix.

INFRARED LUMINESCENCE AT 1010 nm AND 1500 nm IN LiNbO3:Er3+ EXCITED BY SHORT PULSE RADIATION AT 980 nm

Luminescence of LiNbO3:Er3+ crystal at a wavelength of 1010 nm and 1500 nm under pulsed excitation of different power at a wavelength of 980 nm are experimentally and theoretically studied. It is revealed, that the main part of the absorbed energy gives rise to the luminescence at 1500 nm. Considered concentrations of Er3+ impurity ions allow to exclude cooperative processes in the impurity subsystem. The experimental results are interpreted in the framework of a three electronic levels system, assuming that the population of the higher lasing level 4I13/2 in the crystal under study is caused by relaxation processes from the excited level. It is shown that for obtaining of a laser radiation at about 1500 nm one can effectively use a pulse-pumping at 980 nm with a power density in a range of 50 ÷ 60 MW/cm2.

Enhanced two-photon-absorption using sub-wavelength antennas

Degenerate two-photon absorption (TPA) is investigated in a 186 nm thick gallium arsenide (GaAs) p-i-n diode embedded in a resonant metallic nanostructure. The full device consists in the GaAs layer, a gold subwavelength grating on the illuminated side, and a gold mirror on the opposite side. For TM-polarized light, the structure exhibits a resonance close to 1.47 μm, with a confined electric field in the intrinsic region, far from the metallic interfaces. A 109 times increase in photocurrent compared to a non-resonant device is obtained experimentally, while numerical simulations suggest that both gain in TPA-photocurrent and angular dependence can be further improved. For optimized grating parameters, a maximum gain of 241 is demonstrated numerically and over incidence angle range of (−30°; +30°). This structure paves the way towards low-noise infrared detection, using non-degenerate TPA, involving two photons of vastly different energies in the same process of absorption in a large bandgap semiconductor material.