I.M. Catalano

Optical gain in GaSe due to exciton-exciton recombination☆

Abstract Measurements of the optical gain spectrum in high quality GaSe are reported. The mechanism for light amplification has been investigated, giving evidence that the exciton-exciton scattering process is responsible for stimulated emission.

Stimulated emission of GaN under high one and two quantum excitation

Abstract Stimulated emission at 3.435 eV in GaN at 80 K is reported. This emission is attributed to a cooperative excitonic process and is observed only in undoped samples. One and two photon optical pumping has been used and optical gain of about 103 cm-1 has been measured.

Two-photon absorption coefficient spectrum in CdSSe nanocrystals by nonlinear luminescence technique

Abstract Low-temperature two-photon absorption measurements on semiconductor doped glasses containing CdS 1− x Se x particles of various average sizes have been reported. Such experimental results have been shown to be in good agreement with the effective-mass-approximation calculations in which the contributions of the different valence sub-bands have been taken into account. Furthermore, the two-photon absorption coefficient has been experimentally measured and the imaginary part of the third-order susceptibility has also been evaluated.

Second harmonic generation in InSe

Abstract Experimental evaluation of non-linear susceptibility coefficient d22 for InSe, which is responsible for second harmonic generation in this material at 1.06 and 10.6 μm, is reported and the value compared with GaSe. At the CO2 laser frequency of oscillation, phase matching has been observed and a value of d22 almost equal to d15 for CdSe has been found. The InSe high transparency in the wavelength range 1.1–22 μm, the sizeable value of d22 and the possibility of reaching phase matching condition in the IR range make InSe a potential device for far IR frequency conversion.

Frequency dependence of interband two-photon absorption mechanisms in ZnS and CdI2

The transition mechanism changes involved in direct interband two-photon absorption (TPA) processes have been studied in two II–VI compounds:ZnO and ZnS. The experimental results have indicated that the transition mechanism nature changes when the excitation energy is varied. The transitions are of an allowed-allowed type near the energy gap and become of an allowed-forbidden type far from it. In particular, for ZnO when 2ħw-Ey > ~ 400 meV the first experimental evidence of a dominant mechanism of forbidden-forbidden type has been obtained. Furthermore, the spectral behaviour of the TPA coefficient (α(2)) has been well described by a parametric formula containing terms (with different energy dependences) related to the above-mentioned different transition mechanisms.

Non-parabolic band effect on two-photon absorption in ZnSe and CdTe

Abstract Absolute two-photon absorption coefficients have been measured in ZnSe and CdTe single crystals by means of the two-channel normalization technique. Comparison between TPA experimental and theoretical values shows that the TPA, for 2 h ω ⪢ E g , is oddly influenced both by non-parabolicity and degeneracy of the energy bands.

Excitonic properties in Zn1−xCdxSe/ZnSe multi‐quantum well structures by one‐ and two‐photon spectroscopy

A detailed investigation of excitonic states by means of one‐ and two‐photon absorption photoluminescence excitation spectroscopy in Zn1−xCdxSe/ZnSe multi‐quantum wells is reported. Ground state and excited heavy‐ and light‐hole excitons associated with the n=1,2 subbands have been selectively probed exploiting the different selection rules governing one‐ and two‐photon absorption processes. Experimental exciton transition energies are found to be in good agreement with theoretical predictions when strain and confinement effects are included. The comparison between experiments and theory allowed us to single out a well defined set of band parameters and to gauge the band‐offsets in these heterostructures. Furthermore, the absorption band edge clearly evident in the two‐photon absorption photoluminescence excitation spectra allowed us to directly measure excitonic binding energies with good accuracy.

Spectral behavior of three-photon absorption coefficient in II–VI compounds: ZnO, CdS and ZnSe

Abstract Three-photon absorption (3PA) spectra has been experimentally investigated in a large excitation energy range above the optical gap for three II–VI semiconductors (ZnO, CdS and ZnSe) with different band structures. The spectral behavior of 3PA coefficient has been demonstrated to be described by a parametric formula containing a varying number of different terms, whose energy dependence being predicted on the grounds of 3PA selection rules. A comparison between experimental and theoretical line-shapes has suggested that almost a linear k -dependence approximation for the optical matrix elements has to be always assumed in order to correctly describe the 3PA coefficient line shape.

Three-photon absorption coefficient in ZnSe and ZnO☆

Abstract Three-photon absorption coefficient (α (3) ) measurements have been carried out in ZnSe and ZnO single crystals by quantitative non-linear luminescence method by using both a neodymium—YAlG and a ruby laser. The comparison between the α (3) and α (3) α (2) experimental data and the numerical results of theoretical perturbative and non-perturbative approaches has been carried out.

Non-linear self-action effect and absolute two-photon absorption coefficient in CdS

Abstract The role of non-linear self-action (SA) effect on absolute two-photon absorption (TPA) coefficient measurements has been quantitatively evaluated in CdS. The SA-effect and the absolute TPA coefficient have been measured by “external SA” and “one-channel” method respectively, using a single mode ruby laser. When the SA-effect has been taken into account, a sensible variation in TPA coefficient evaluation has been found.