Optical and ultrasonic monitoring of femtosecond laser filamentation in fused silica

Millimeter-long filaments and accompanying luminous plasma and defect channels created in fused silica (FS) by single focused femtosecond laser pulses with supercritical powers were probed in situ using optical imaging and contact ultrasonic techniques. Above the threshold pulse energy E_opt = 5 μJ corresponding to a few megawatt power levels pulses collapse due to self-focusing, producing channels filled by electron-hole plasma and luminescent defects, and exhibits predominantly compressive pressure transients. Analysis of the optical and ultrasonic response versus the laser pulse energy suggests that filamentary pulse propagation in the channels occurs with considerable dissipation of about ∼10 cm⁻¹. The predominant ionization mechanism is most likely associated with avalanche ionization, while the main mechanism of optical absorption is free-carrier absorption via inverse Bremsstrahlung interaction with the polar lattice.     

Novel method to determine the actual surface area of a laser-nanotextured sensor

The actual surface area of a gold-coated conductive layer over the laser nano-textured surface of sapphire is determined using an electrochemical cyclic voltammetry. The method is down scaled to measure the sensing surface area of 200 × 200 μm² on a laser-ablated ripple sensor used for surface-enhanced Raman spectroscopy/scattering (SERS). Ripple SERS sensors made on different substrates of high refractive index materials such as GaP, diamond, SiC, and Al₂O₃ make a versatile sensing platform with the detection of analyte (here a thiophenol) down to 10 nM concentrations. Direct measurement of the surface area provides a powerful tool to investigate roughness, porosity, and morphology of coatings used for SERS or other light harvesting surfaces such as solar cells. Novelty of the proposed method is in the use of cathodic peak of surface passivation–activation cycle for calculation of surface charge. The method enables high-accuracy surface area measurements from as small as 0.01 mm² pads up to functional solar cells.     

Laser induced memory bits in photorefractive LiNbO3 and LiTaO3

We study experimentally the formation of refractive index voxels (volume elements) in photorefractive LiNbO₃ and LiTaO₃ crystals illuminated with high irradiance femtosecond laser pulses. We used 150 fs pulses at 800 nm wavelength (energy 6–50 nJ) tightly focused inside the crystals in a single shot regime. This resulted in a formation of a micrometer size region of elevated refractive index, which may be used as memory bits in information storage/retrieval application. The maximum refractive index change of 5×10⁻⁴ was recorded in undoped LiNbO₃ at an average light intensity of ∼TW/cm² that is close to the breakdown threshold. A simple setup for photorefractive recording and in situ monitoring of the refractive index changes has been proposed. M. Sūdžius leaves from: the Institute of Materials Science and Applied Research of Vilnius University, Lithuania.     

The Evidence of the Bystander Effect after Bleomycin Electrotransfer and Irreversible Electroporation

One of current applications of electroporation is electrochemotherapy and electroablation for local cancer treatment. Both of these electroporation modalities share some similarities with radiation therapy, one of which could be the bystander effect. In this study, we aimed to investigate the role of the bystander effect following these electroporation-based treatments. During direct CHO-K1 cell treatment, cells were electroporated using one 100 µs duration square wave electric pulse at 1400 V/cm (for bleomycin electrotransfer) or 2800 V/cm (for irreversible electroporation). To evaluate the bystander effect, the medium was taken from directly treated cells after 24 h incubation and applied on unaffected cells. Six days after the treatment, cell viability and colony sizes were evaluated using the cell colony formation assay. The results showed that the bystander effect after bleomycin electrotransfer had a strong negative impact on cell viability and cell colony size, which decreased to 2.8% and 23.1%, respectively. On the contrary, irreversible electroporation induced a strong positive bystander effect on cell viability, which increased to 149.3%. In conclusion, the results presented may serve as a platform for further analysis of the bystander effect after electroporation-based therapies and may ultimately lead to refined application of these therapies in clinics.     

Highly Efficient Candlelight Organic Light-Emitting Diode with a Very Low Color Temperature

Low color temperature candlelight organic light-emitting diodes (LEDs) are human and environmentally friendly because of the absence of blue emission that might suppress at night the secretion of melatonin and damage retina upon long exposure. Herein, we demonstrated a lighting device incorporating a phenoxazine-based host material, 3,3-bis(phenoxazin-10-ylmethyl)oxetane (BPMO), with the use of orange-red and yellow phosphorescent dyes to mimic candlelight. The resultant BPMO-based simple structured candlelight organic LED device permitted a maximum exposure limit of 57,700 s, much longer than did a candle (2750 s) or an incandescent bulb (1100 s) at 100 lx. The resulting device showed a color temperature of 1690 K, which is significantly much lower than that of oil lamps (1800 K), candles (1900 K), or incandescent bulbs (2500 K). The device showed a melatonin suppression sensitivity of 1.33%, upon exposure for 1.5 h at night, which is 66% and 88% less than the candle and incandescent bulb, respectively. Its maximum power efficacy is 23.1 lm/W, current efficacy 22.4 cd/A, and external quantum efficiency 10.2%, all much higher than the CBP-based devices. These results encourage a scalable synthesis of novel host materials to design and manufacture high-efficiency candlelight organic LEDs.