Stimulated emission in silicon nanocrystals: gain measurement and rate equation modelling

Luca Dal Negro, Lorenzo Pavesi, Georg Pucker +2 more

Syed Iftekhar Ali

Kateřina Dohnalová, Karel Žídek, Lukáš Ondič +3 more

In this paper we present time-resolved optical gain spectroscopy using the variable stripe length technique in combination with the shifting excitation spot technique under pumping with nanosecond laser pulses. Measurements reveal positive optical gain on a nanosecond time scale at 430 nm (F-band), accompanied by spectral narrowing and a threshold behaviour of the amplified spontaneous emission as a function of the excitation intensity. We show that the presence of the slow-red (S-band) emission component critically influences the observation of stimulated emission from the F-band.

Mile Ivanda, W. Kiefer, Carl W. White +1 more

Luca Dal Negro, M. Cazzanelli, Beniamino Danese +4 more

Net optical gain in silicon nanocrystals (Si-nc) has been measured by pump and probe transmission experiments. Si-nc active layers have been produced by plasma enhanced chemical vapor deposition on transparent quartz substrates. Continuous and pulsed pump and probe transmission measurements have shown clear evidences of net probe amplification with fast (nanosecond) response time. Transfer matrix and rate equations modeling of the nonlinear signal transmission allowed to extract the gain spectra for different pump intensities yielding good qualitative agreement with the experimental data. Gain cross sections per nanocrystals of the order of 3×10−16cm2 have been deduced. The physical origin of the optical amplification is interpreted within a four level recombination model describing the dynamics of strongly localized excitons at the Si-nc∕SiO2 interface.

Stefano Bottacchi

Introduction In this chapter we will present the theory of spectral gain in optical amplifiers and the related optical power distribution. The concepts are general, as they apply to every optical amplifier configuration, independent of the specific architecture and implementation technology. We will configure the optical amplifying medium as a traveling-wave device, where the optical field undergoes optical amplification as it propagates from the input to the output sections. Generally speaking, optical amplification is achieved by a net stimulated emission process. Referring to a generic section z of infinitesimal thickness dz , optical gain is determined by the imbalance between net stimulated emission and cavity losses, including extrinsic absorption, reflection and radiated fields. As we know from the theory of light amplification in the three-level atomic system presented in Chapter 5, stimulated absorption of photons is governed by the same transition rate as stimulated emission, and is included in the net stimulated emission process. With this in mind, we note the identity between stimulated emission and the stimulated absorption rates, Γ 12 = Γ 21 , and the net stimulated photon term Γ[ j 2 ( t ) – j 1 ( t )] p ( t ) in the rate equation. In order to develop the traveling-wave model, the photon density becomes a function of the longitudinal position 0 ≤ z ≤ L along the amplifier medium. Accordingly, we will set p ( t , z ) as the relative density of stimulated photons per unit volume (0 ≤ p ( t , z ) ≤ 1) at time t and section z . When photons with appropriate energy proceed along the amplifying medium, they are amplified by means of net stimulated emission. At some section z = z 0 , the steady-state photon density P ( z ) can approach the saturation density P sat ( z ).