The hybrid electronically addressable random (HEAR) laser is a novel type of random fiber laser that presents the remarkable property of selection of the fiber section with lasing emission. Here we present a joint analysis of the correlations between intensity fluctuations at distinct wavelengths and replica symmetry breaking (RSB) behavior of the HEAR laser. We introduce a modified Pearson coefficient that simultaneously comprises both the Parisi overlap parameter and standard Pearson correlation coefficient. Our results highlight the contrast between the correlations and presence or not of RSB phenomenon in the spontaneous emission behavior well below threshold, replica-symmetric ASE regime slightly below threshold, and RSB phase with random lasing emission above threshold. In particular, in the latter we find that the onset of RSB behavior is accompanied by a stochastic dynamics of the lasing modes, leading to competition for gain intertwined with correlation and anti-correlation between modes in this complex photonic phase.

There is already a societal awareness of the growing impact of nanoscience and nanotechnology, with nanomaterials (with at least one dimension less than 100 nm) now incorporated in items as diverse as mobile phones, clothes or dentifrices. In the healthcare area, nanoparticles of biocompatible materials have already been used for cancer treatment or bioimaging enhancement. Nanotechnology in dentistry, or nanodentistry, has already found some developments in dental nanomaterials for caries management, restorative dentistry and orthodontic adhesives. In this review, we present state-of-the-art scientific development in nanodentistry with an emphasis on two imaging techniques exploiting nanomaterials: optical coherence tomography (OCT) and photoacoustic imaging (PAI). Examples will be given using OCT with nanomaterials to enhance the acquired imaging, acting as optical clearing agents for OCT. A novel application of gold nanoparticles and nanorods for imaging enhancement of incipient occlusal caries using OCT will be described. Additionally, we will highlight how the OCT technique can be properly managed to provide imaging with spatial resolution down to 10′s–100′s nm resolution. For PAI, we will describe how new nanoparticles, namely TiN, prepared by femtosecond laser ablation, can be used in nanodentistry and will show photoacoustic microscopy and tomography images for such exogenous agents.

Silva EJ, et al. Imaging Sci Dent. 2021 Jun;51(2):107-115. https://doi.org/10.5624/isd.20200259

Combining photonic excitation and acoustic detection, photoacoustic imaging (PAI) presents one of the most promising noninvasive biomedical diagnostic modalities, but this technique still lacks efficient nano-sized contrast agents absorbing light in the region of relative tissue transparency (630–900 nm). Here, we explore the use of titanium nitride (TiN) nanoparticles (NPs) fabricated by methods of pulsed laser ablation in liquids as a contrast agent in PAI. When prepared in acetone, the NPs are spherical, have an average size of 25 nm, and exhibit a broad plasmonic absorption peak around 700 nm. We show that solutions of these NPs render possible a strong nonlinear photoacoustic response and the generation of photoacoustic images with 67 μm resolution within the biological transparency window. The observed effect is explained by a plasmonically enhanced two-photon absorption process in TiN NPs. Combined with earlier demonstrated capability of generating photothermal therapeutic effect, relative chemical purity, and excellent biocompatibility, laser-synthesized TiN NPs promise attractive applications in biomedical theranostics involving imaging modalities based on photoacoustics microscopy or tomography.

We propose a cost-effective light emitting diode based photoacoustic computed tomography (LED-PACT) system integrating a custom nanosecond pulsed LED array with a single-element ultrasound transducer for circular scanning. An LED array consisting of 37 LEDs, driven by a homemade nanosecond pulsed current source (NSPCS) driver, provided 100 ns optical pulse width (850 nm wavelength), 0.18 mJ per pulse energy (8 kHz pulse repetition rate). We compared the performance of the LED-PACT in terms of imaging depth, resolution, signal-to-noise ratio (SNR) against pulsed laser diode (PLD) based PACT. Phantom and tissue studies demonstrate our LED-PACT’s competitive imaging performance, including a SNR of 22.4 dB (with 2.25 MHz UST), comparable spatial resolution of 178 µm (with 5 MHz UST) and a practical imaging depth of 20 mm in chicken tissue, despite operating at significantly lower optical energies than PLD (0.18 mJ vs 1.88 mJ). With a fraction of cost (<$1,000) compared to any other light sources used in PACT, this LED-PACT system holds promise for portable PA imaging system for widespread and safe clinical translation.

Photoacoustic imaging (PAI) is gaining attention for its non-invasive diagnostic capabilities. Traditionally, bulky and expensive laser systems have been used as excitation light sources in PAI, posing challenges for translation and remote applications. High-power light emitting diodes (LEDs) can be an alternative light source. However, the necessary driver circuitry has not been extensively studied for driving the nanoseconds pulsed LEDs. This study develops and demonstrate for the first time the full circuit, performance, optimization and operating procedures of a nanosecond pulsed current source (NSPCS) to drive a high-power, high-speed LED array for PAI. The NSPCS driver can deliver tunable pulsed LED currents between 0 and 20 A, pulse widths of 50–100 ns, and trigger pulse repetition rates up to 20 kHz, achieving a driver efficiency of 58.27%. It can drive an array of 37 high-power LEDs (850 nm wavelength) with an electrical-to-optical efficiency of 24.8%. Illumination with this LED array produced a photoacoustic signal (after 79 dB amplification with low-noise amplifier) of 3.92 V (peak-to-peak) and a signal-to-noise ratio of 79.36 dB. The NSPCS circuit has demonstrated effective generation of tunable high-current pulses for LED-based PAI applications.