Laser Goggles Research Articles

Excited state absorption induced optical limiting action of MoS2-rGO nanocomposites

Molybdenum sulphide-reduced graphene oxide nanocomposite made of microsphere MoS2 with varying concentration of layered (15, 30, 45 wt%) rGO was prepared by hydrothermal method. XRD confirms the molecular formation of mixed phase MoS2 having rich semiconducting hexagonal phase with traces of metallic tetragonal phase (1T@2H MoS2) and reduced graphene oxide (2θ = 25.7°, (002)). Further EDS also ascertains the reduction of Mo and S with increase in C content with respect to rGO concentration. As the rGO concentration increases (15–45 wt%), strengthening of characteristic Raman peaks of rGO (G and D band) and weakening of MoS2 (E1g, E2g1 and A1g modes) in composite was observed. Estimated ID/IG (1.04) and I2D/IG (0.62) ratio suggest the formation of 2–3 layers of graphene. SEM depicts layered morphology of rGO, floret like microstructure of MoS2 and floret microspheres MoS2 decorated rGO layers of MoS2 – rGO nanocomposite. Optical studies show absorption peaks at 266 nm (π-π* transition of the CC aromatic bonds of graphene), 370 nm (and n-π* transition of the CO bond of graphene) and 330 nm (direct transitions in valence to conduction band of MoS2). Liquid dispersion of both pristine and composite depicted strong absorption in UV–Visible region and available electronic state favours the opportunity for two-photon absorption. Intensity dependent Z-Scan with nano-pulsed green laser excitation shows the existence of excited state absorption involved two-photon absorption. Variation of saturation intensity and nonlinear absorption coefficient with on-axis peak intensity (620 –2160 GW/cm2) confirms the involvement of sequential 2PA process (1PA + ESA). MoS2-(30 wt%)rGO nanocomposite exhibited higher 2PA coefficient (9.42 × 10−10 m/W) and lower onset optical limiting threshold (3.15 × 1012 W/m2) than its pristine counterparts and other well-known TMDC’s and graphene derivatives. Enhanced NLO response is due to synergistic effects of rGO (higher defect induced states, extended conjugation for charge transfer) and MoS2 (floret morphology, uniform decoration and strong visible absorption). Observed excited state absorption induced energy absorbing optical limiting action of MoS2-rGO nanocomposite with augmented NLO coefficients open up potential horizon for developing laser goggles against most sensitive and widely used nanopulsed green laser.

Intensity-dependent two-photon absorption and its saturation in 2-methyl 4-nitroaniline nanofibers

The Nonlinear absorption and its optical limiting properties of 2-methyl 4-nitroaniline-polymethylmethacrylate (2M4NA-PMMA) electro-spun nanofibers are investigated by Z-scan technique using Q switched Nd:YAG laser as an excitation source (532 nm, 5 ns, 10 Hz). Open-aperture measurements show that 2M4NA-PMMA nanofibers exhibit reverse saturable absorption. Intensity-dependent two-photon absorption coefficient demonstrates the presence of sequential two-photon absorption process involving real resonant intermediate states. The incorporation and orientation of 2M4NA in PMMA nanofibers are analyzed by XRD and it is found to range from 38 nm to 43 nm of crystallite size. SEM images illustrate the formation of smooth fibers using electrospinning by applying different voltages (12, 14, 17 kV). Ground-state absorption analysis shows that the nanofibers possess maximum absorption around 400 nm with a optical transmittance window (410–1200 nm) in the wide range of entire visible and NIR region. Lower optical limiting threshold (0.97 to 1.79 × 1012 W/m2) of 2M4NA-PMMA nanofibers ensures the suitability of optical fibers as optical limiters towards the development of laser goggles for pulsed green laser.

Perceptions and Practice Patterns of Holmium Laser Goggles in Endourological Procedures: An Unnecessary Evil?

The holmium laser is used increasingly for a wide array of urological procedures. Laser safety goggles are mandatory at many centers for individuals within the nominal hazard zone, as set out by the institution. Recent ex vivo studies suggest standard eye wear may be equally as protective. We sought to evaluate the perceptions and practice patterns of laser safety goggles in urology. A 24-question survey was sent out through e-mail to an international e-mail list of ∼2000 urologists that were members of the Endourological Society. Data were collected anonymously using Survey Monkey. A total of 264 (14%) urologists completed the survey. Thirty-four percent worked in the community, whereas 63% worked at an academic institution. Ninety-seven percent routinely used the holmium laser. The most common uses were lithotripsy (99%), tissue incision (71%), tumor ablation (58%), and prostate ablation (26%). Formal laser training and institutional laser safety policies were reported in 76% and 64%, respectively. Forty percent of respondents routinely wore laser safety goggles. Laser adverse events were witnessed by 19%, but there were no eye injuries reported. Seventy percent of surgeons felt that laser safety goggles may impair their vision. When presented with the information that regular eye glasses may be as effective as laser goggles for preventing harm, the majority (86%) would opt for regular eye wear. Laser safety eyewear practice patterns vary greatly. Many centers have adopted policies for universal mandatory laser goggles in the operating room. With over two thirds of surgeons suggesting laser goggles impair their vision, and recent literature suggesting regular eye wear is equivalent in preventing laser-associated eye injuries, laser goggle safety policies should be updated to better match the potential hazards inherent to the device.

Messsystem zur Bestimmung von Farbunterscheidungsschwellen bei Farbsinnstörungen und unter Einfluss von farbigen Filtern

In clinical practice, several techniques for the evaluation of colour vision deficiencies are well established. Most of them are designed for the detection of congenital or pathological changes. Due to the narrow-banded light sources, used in monitors or anomaloscopes, the human gamut can be addressed only in part. With these set-ups, the impact of coloured filters on colour vision such as blue light filtering intraocular lenses cannot be investigated precisely. The technique is based on the visual matching of colour differences between two halves of a test field. The colours are generated by mixing seven types of LEDs. A transparent, vertically divided circular test field is retro-illuminated with this light using optical fibres and projection optics. An ocular optic assures the unaccommodated sight of the subject on the test field (size 2 degrees). The developed set-up presents freely adjustable colours in the form of continuous light spectra to examine the influence of filter materials on colour discrimination. A colour space can be generated which corresponds to that of human perception. The saturation and brightness of the light is adjustable. The subject has to decide if he can discriminate between the colours in the test field halves or not. Before the next colours are shown the subject is neutrally adapted by a neutral hue to provide different adaptation levels. The luminescence of the test field can be varied up to 1500 cd/m(2). The adaptive algorithm of the sequence is based on the SIAM method described by Kaernbach. Based on reference measurements, including 4 subjects with a congenital deficiency, it was shown that the discrimination thresholds at the characteristic confusing axes are significantly different than those with normal colour vision. Also, the impact of green laser goggles on the colour perception was determined. Due to the filter the thresholds in the vicinity of yellow (x = 0.4664; y = 0.4525) are reduced in the yellow-orange and cyan range and increased in the green-yellow and magenta range. With this set-up an objective instrument is available for clinical research in the field of individual human colour perception. It enables an accurate and detailed analysis of the impact of coloured filters as well as a quantitative detection of congenital anomalies. The adaptive algorithm allows short sequences and precise determination of colour discrimination thresholds.