Near-IR absorption saturation and mechanism of picosecond recovery dynamics of copper selenide nanostructured via alumina

Abstract

Absorption saturation at 1.064 μm wavelength in Cu2−xSe material nanostructured by means of an original method—formation and hosting in an array of electrochemically grown alumina voids—was investigated. Columnlike channels provide growth of copper selenide in a shape of nanowire with a fixed diameter. Experimental results obtained from measuring nanowires of various diameters (∅10, 15, 20, and 70 nm) revealed that the ∅20 nm case is most efficient for absorption saturation, manifesting highest optical modulation depth and lowest interlevel transition rate evaluated. A model to analyze the conditions for absorption saturation and absorption recovery dynamics was developed. Depending on pump intensity the nonmonotonous increase in recovery time for the highest applied values was interpreted as filling up of states at an intermediate energy level. From modeling, important material science parameters, such as concentration of resonant and trapping/recombination states, interlevel transition rate, capture time, characteristic for copper selenide, have been evaluated and compared for different samples. Finally, the consequence of the model to a working copper selenide energy level scheme was considered.

Effect of hydrogen doping on the loading of titania nanotube films with copper selenide species via alternating current deposition

“…It is reasonable to mention that similar solution has been suggested by us earlier for porous alumina coloring [11][12][13][14]. As seen, in this solution under the constant AC peak-to-peak voltage (U p-to-p ) mode, densely packed crystallites in size of from 60 to 160 nm appear to be deposited mainly at the TiNT film surface.…”

“…No reports, however, have been dedicated to the application of p-type selenide species that can be organized in both stoichiometric (CuSe, Cu 2 Se, CuSe 2 , Cu 2 Se 3 ) or non-stoichiometric (Cu 2-x Se) composition. As reported previously, copper selenide nanowired arrays encased in alumina matrices and glasses behave as a direct band gap of 2.2 to 2.4 eV and an indirect band gap of 1.1-1.7 eV light absorbers [11][12][13][14][15]. Therefore, in this study, we attempted to couple copper selenide species with TiO 2 by alternating current (AC) deposition from appropriate aqueous solution comprising Cu 2?…”

Picosecond absorption relaxation measured with nanosecond laser photoacoustics

“…In the transmission-based approach, the relaxation time is extracted by measuring pump-induced changes in probe-beam transmittivity ⌬T = T͑I p ͒ − T͑0͒, where T͑I p ͒ and T͑0͒ are the probe beam transmittivities with and without a pump of intensity I p . 9 In both approaches, the time resolution is limited by the pulse width of both the pump and the probe pulses. Hence, not only is an expensive picosecond or femtosecond laser required, but also the detection is susceptible to pulse broadening in dispersive media.…”

“…[5][6][7] Typically, relaxation times are studied via an ultrafast ͑femtosecond or picosecond͒ pump-probe technique by measuring either fluorescence in a reflection configuration or absorption in a transmission configuration. 8,9 In the reflection-based approach, the molecules are excited by a laser pulse through the transition ͉0͘ → ͉i͘. A probe pulse with a variable delay time relative to the pump pulse monitors the time evolution of the population density N i ͑t͒.…”

Nonlinear mechanisms in photoacoustics—Powerful tools in photoacoustic imaging

“…Absorption saturation-based nonlinearity can be employed to determine the absorption relaxation time [ 23 ], which is a significant parameter in understanding the transient relaxation energy transfer processes as it relates to many photophysical and photochemical reactions, such as photosynthesis [ 62 ], photolysis [ 63 ] and transient changes in the molecular structure [ 64 ]. is a picosecond-scale parameter and generally measured using the femto/picosecond pump-probe technique [ [65] , [66] , [67] , [68] , [69] ], which is not only costly but also susceptible to pulse broadening in dispersive media. Danielli et al [ 23 ] applied the nonlinear mechanism to quantify for the first time, where is extracted by fitting the theoretical PA– F curve ( Fig.…”