In this work, we developed and investigated a random laser based on rhodamine6G (Rh6G) in ethylene glycol (EG) solution with varying cellulose nanocrystalline (CNC) needles as scatterers in the lasing media. Besides the suspension-in-cuvette scheme, an alternative configuration was also employed: a dye-CNC flexible self-supported thick-film (70 µm) random laser made by drop casting of the C N C s + R h 6 G + h y d r o x y p r o p y l cellulose suspension. In relation to conventional scatterers, the biodegradable cellulose nanocompounds showed a comparable reduction in both the spectral full width at half-maximum and the energy threshold values, with an optimal concentration of 5 mg [CNC]/ml[EG] in suspension. Its performance was also compared with other cellulose-based random lasers, presenting advantages for some parameters. The flexible film configuration showed similar results, but contained 10% less Rh6G than the suspension.

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The focused signal obtained by the time-reversal or the cross-correlation techniques of ultrasonic guided waves in plates changes when the medium is subject to strain, which can be used to monitor the medium strain level. In this paper, the sensitivity to strain of cross-correlated signals is enhanced by a post-processing filtering procedure aiming to preserve only strain-sensitive spectrum components. Two different strategies were adopted, based on the phase of either the Fourier transform or the short-time Fourier transform. Both use prior knowledge of the system impulse response at some strain level. The technique was evaluated in an aluminum plate, effectively providing up to twice higher sensitivity to strain. The sensitivity increase depends on a phase threshold parameter used in the filtering process. Its performance was assessed based on the sensitivity gain, the loss of energy concentration capability, and the value of the foreknown strain. Signals synthesized with the time–frequency representation, through the short-time Fourier transform, provided a better tradeoff between sensitivity gain and loss of energy concentration.

Resumo-Monitorar o nível de deformação é crucial em diversas aplicações. Sinais de ultrassom em meios reverberantes podem ser utilizados para esse fim através da observação do valor de pico do sinal obtido pela técnica de reversão temporal ou pela correlação cruzada. Neste artigo, apresentamos uma modificação dessa técnica em que um sinal de referência é alterado a partir de um processo de filtragem utilizando a transformada de Fourier de tempo curto, a fim de aumentar a sensibilidade do sinal à deformação. Essa técnica foi avaliada em sinais experimentais e foi capaz de fornecer um aumento de sensibilidade à deformação de até cerca de cinco vezes. Palavras-Chave-Monitoramento de deformação, sinais de ultrassom, STFT