Random laser emission from whole blood as the active medium.

We introduce a proof of concept for multimode random laser (RL) emission with fresh whole blood (WB) as the active medium. The experimental principle is adapted from RL emission using rhodamine 6G (R6G). We achieved conditions for fresh WB to fluoresce with stochastic amplification of stimulated emission of radiation. The random conditions are placed with SiO2 particles, suspended in isotonic solvent. The results we report are for: (1) R6G-RL, with 2 nm bandwidth centered at 567 nm, and (2) RL emission for WB at 969 nm and 437 nm, of sub-3 nm bandwidth. For validation purposes, we show that the pumping energy threshold for RL emission from blood is consistent with R6G-RL.

Frequency analysis for an extended photoacoustic transport model.

In photoacoustic imaging, the signal attenuation is a well-known source of artifacts over the image reconstruction. It is recognized that this is caused by optical absorption effects and by the ultrasound broadband scattering. However, the sound dispersion is generally neglected, although it appears notably in thick or heterogeneous tissues. In the present Letter, we give an experimental example in which both attenuation and sound dispersion are dealt with as relevant features to be taken into consideration. An analytic perspective of these perturbations leads us to a waveform transport-model extension that provides a linear description of the induced acoustic effects. We find a near match between the theoretical predictions and the experimental results in the frequency domain. These outcomes approximate projection data that represent forward solutions in photoacoustic image reconstruction.

Angular distribution of random laser emission.

We present an experimental analysis of the angular distribution of the emission of a random laser (RL) operating in the diffusive regime (∼1% volume fraction of scatterers). The RL ensemble was made of silica particles suspended in a 1:1 methanol:water matrix with Rhodamine 6G dye as the active medium. We found that, for specific pumping-energy-dependent scattering strength, the RL spectrum reached stable features that were angularly preserved. From the analysis, we propose that this defines a novel parametric condition that may well be the equivalent of the RL critical volume, as proposed by Letokhov.