SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Fiber laser

28

BACKGROUND: Melasma is a common acquired symmetrical hyperpigmentation that is often recurrent and refractory. OBJECTIVES: To investigate the efficacy and safety of a single administration of high-density fractional thulium fiber laser (1,927 nm) for the treatment of refractory melasma in 20 patients. MATERIALS AND METHODS: A retrospective chart and photographs review of 20 women (Fitzpatrick skin type II-IV) with clinical diagnosis of melasma treated with the 1,927-nm fractionated thulium laser at 10 or 20 mJ/cm(2) , with 60-70% surface area coverage. Four investigators independently evaluated Melasma Area Severity Index (MASI) scores before, 4 weeks, 3-6 months, and 6-12 months after treatment. RESULTS: Mean MASI scores decreased dramatically from 13.2 ± 5.4 before treatment to 8.5 ± 3.5 at 4 weeks after laser treatment (P = 0.004). Patient assessment revealed that 12 of the 20 subjects had more than 50% clearance of their melasma. Recurrence was reported by 7 out of 15 patients who were successfully followed-up (mean 10.2 months). Two patients developed postinflammatory hyperpigmentation that subsided with topical bleaching after 3 months. CONCLUSION: High-density coverage fractional 1,927-nm thulium laser proved to be safe and effective for melasma with long-term remission. Lasers Surg. Med. © 2012 Wiley Periodicals, Inc.

Concepts: Optical fiber, Laser, Infrared, Erbium, Solid-state laser, Lasers, Fiber laser, Raygun

28

We report the development of an all-fiber-optic scanning endomicroscope capable of high-resolution second harmonic generation (SHG) imaging of biological tissues and demonstrate its utility for monitoring the remodeling of cervical collagen during gestation in mice. The endomicroscope has an overall 2.0 mm diameter and consists of a single customized double-clad fiber, a compact rapid two-dimensional beam scanner, and a miniature compound objective lens for excitation beam delivery, scanning, focusing, and efficient SHG signal collection. Endomicroscopic SHG images of murine cervical tissue sections at different stages of normal pregnancy reveal progressive, quantifiable changes in cervical collagen morphology with resolution similar to that of bench-top SHG microscopy. SHG endomicroscopic imaging of ex vivo murine and human cervical tissues through intact epithelium has also been performed. Our findings demonstrate the feasibility of SHG endomicroscopy technology for staging normal pregnancy, and suggest its potential application as a minimally invasive tool for clinical assessment of abnormal cervical remodeling associated with preterm birth.

Concepts: Childbirth, Laser, Tissues, Skin, Cervix, Tissue, Fiber laser

27

In this Letter, multifocus optical-resolution photoacoustic microscopy is demonstrated using wavelength tuning and chromatic aberration for depth scanning. Discrete focal zones at several depth locations were created by refocusing light from a polarization-maintaining single-mode fiber pumped by a nanosecond fiber laser. The fiber and laser parameters were chosen to take advantage of stimulated Raman scattering (SRS) in the fiber to create a multiwavelength output that could then be bandpass filtered. The collimator lens and objective lens are chosen to take advantage of chromatic aberration in which each generated SRS wavelength peak focuses at a slightly different depth. The maximum amplitude of photoacoustic signals is mapped to form C-scan images. Additionally, all wavelength peaks fired simultaneously offers improved depth-of-field structural imaging at the cost of slight degradation of mainlobe-to-sidelobe ratios. Wavelength-tuned depth scanning over more than 440 μm is demonstrated, significantly greater than the ∼100  μm depth of field predicted from our focused Gaussian beams. The improved depth of focus could be valuable for structural imaging of microvascular morphology without the need for mechanical scanning in the depth direction.

Concepts: Optics, Laser, Lens, Raman scattering, Geometrical optics, Rayleigh scattering, Depth of field, Fiber laser

27

Abstract Background: Acne scarring has lifelong sequelae. Fractional photothermolysis (FP) has been shown to provide fast recovery from acne within a short period, thereby aiding skin rejuvenation. Isotretinoin is a well-known, effective drug for the treatment of severe recalcitrant acne. This study investigated the safety and the efficacy of infrared fractional laser treatment in conjunction with low-dose isotretinoin for the treatment of acne and acne scars. Materials: A 1550 nm Erbium-doped fiber laser was used to treat 35 patients with acne scarring. All the patients had taken isotretinoin (10 mg/day) for more than one month prior to the commencement of the fractional laser treatment. Results: There was no aggravation of acne scars, hypertrophic scars, or keloids. Most of the patients (33 patients) received reduced microthermal damage zone (MTZ) treatment. Eighty percent of the treated patients (28 patients) demonstrated more than a fair improvement. The total average score on the global acne scarring classification before treatment was 13.5, and the score after treatment was 11.2. Conclusion: Acne and acne scars can be treated more effectively by concomitant use of an infrared fractional laser with low-dose isotretinoin with reduced MTZ densities. Most patients showed more than a fair improvement, and there was no aggravation of the scars.

Concepts: Scar, Optical fiber, Laser, Acne vulgaris, Keloid, Rosacea, Isotretinoin, Fiber laser

25

Raman spectroscopy allows immediate analysis of stone composition. In vivo stone analysis during endoscopic treatment may offer advantages concerning surgical strategy and metaphylaxis. Urinary stone components were evaluated utilizing an experimental setup of a Raman system coupled to commercial laser fibers.

Concepts: Spectroscopy, Optical fiber, Laser, Raman spectroscopy, Infrared spectroscopy, Kidney stone, Coherent anti-Stokes Raman spectroscopy, Fiber laser

25

Bismuth-doped optical fibers and fiber lasers operating in 1625-1775 nm range have been developed for the first time to the best of our knowledge. Now the existing bismuth-doped lasers, including the result presented in this Letter, can cover O, E, S, C, L, and U telecommunication bands. In addition, new data on the nature of the bismuth-related active center were obtained and discussed.

Concepts: Optical fiber, Greatest hits albums, Fiber laser

24

Surface-enhanced Raman scattering (SERS) and surface-enhanced photoluminescence (SEPL) are emerging as versatile widespread methods for biological, chemical and physical characterization in close proximity of nanostructured surfaces of plasmonic materials. Meanwhile, single-step, facile, cheap and green technologies for large-scale fabrication of efficient SERS or SEPL substrates, routinely demonstrating both broad plasmonic response and high enhancement characteristics, are still missing. In this research, single-pulse spallative micron-size craters in a thick Ag film with their internal nanotexture in the form of nano-sized tips are for the first time shown to demonstrate strong polarization-dependent enhancement of SEPL and SERS responses from a nanometer-thick covering Rhodamine 6G layer with average enhancement factors of 40 and 2•106, respectively. Additionally, first detailed experimental study is reported for physical processes, underlying the formation mechanisms of ablative nanotextures on such “thick” metal films. Such mechanisms are demonstrating a complex “hybrid” fluence-dependent ablation character - appearance of spallative craters, typical for bulk material, at low fluences and formation of upright standing nanotips (frozen nanojets), usually associated with thin-film ablation, in the crater centers at higher fluences. Moreover, special emphasize was made on the possibility to reshape nanotopography of such spallative craters through multi-pulse laser-induced merging of their small nanotips into larger ones. The presented approach holds a promise to be one of the cheapest and easy-to-implement way toward mass-fabrication of various efficient spallation-nanotextured single-element plasmonic substrates for routine chemo- and biosensing, using MHz-repetition-rate femtosecond fiber laser sources with multiplexed laser-beams.

Concepts: Scattering, Raman spectroscopy, Demonstration, Raman scattering, Rhodamine 6G, Impact crater, Fiber laser, Raman amplification

3

Random distributed feedback fiber Raman lasers, where the feedback mechanism is provided by Rayleigh backscattering, have attracted a good deal of attention since they were first introduced in 2010. Their simple and flexible design, combined with good lasing efficiency and beam quality properties, comparable to those of standard cavity lasers, have led to multiple applications, particularly in the fields of fiber sensing and optical communications. In spite of these advances, the polarization properties of random fiber Raman lasers, which can strongly affect their performance in both sensing and communications, have barely been explored so far. In this article we experimentally and theoretically study the polarization properties of different open-cavity laser designs, based on either standard transmission fibers or low polarization-mode-dispersion spun fibers. By using high-power, highly-polarized pumps, we demonstrate controllable polarization-pulling and simultaneous lasing at close wavelengths with different output polarization properties in random distributed feedback fiber Raman lasers. These results advance our understanding of the polarization dynamics in ultralong lasers, and pave the way to the design of novel fiber laser sources capable of polarization-sensitive sensing and distributed amplification.

Concepts: Light, Optical fiber, Laser, Oscillation, Control theory, Laser beam profiler, Fiber laser, Raman laser

2

The wavelength tunability of conventional fiber lasers are limited by the bandwidth of gain spectrum and the tunability of feedback mechanism. Here a fiber laser which is continuously tunable from 1 to 1.9 μm is reported. It is a random distributed feedback Raman fiber laser, pumped by a tunable Yb doped fiber laser. The ultra-wide wavelength tunability is enabled by the unique property of random distributed feedback Raman fiber laser that both stimulated Raman scattering gain and Rayleigh scattering feedback are available at any wavelength. The dispersion property of the gain fiber is used to control the spectral purity of the laser output.

Concepts: Light, Laser, Scattering, Raman spectroscopy, Wavelength, Raman scattering, Rayleigh scattering, Fiber laser

2

Random fiber lasers operating via the Rayleigh scattering (RS) feedback attract now a great deal of attention as they generate a high-quality unidirectional laser beam with the efficiency and performance comparable and even exceeding those of fiber lasers with conventional cavities. Similar to other random lasers, both amplification and random scattering are distributed here along the laser medium being usually represented by a kilometers-long passive fiber with Raman gain. However, it is hardly possible to utilize normal gain in conventional active fibers as they are usually short and RS is negligible. Here we report on the first demonstration of the RS-based random lasing in an active fiber. This became possible due to the implementation of a new Bi-doped fiber with an increased amplification length and RS coefficient. The realized Bi-fiber random laser generates in a specific spectral region (1.42 μm) exhibiting unique features, in particular, a much narrower linewidth than that in conventional cavity of the same length, in agreement with the developed theory. Lasers of this type have a great potential for applications as Bi-doped fibers with different host compositions enable laser operation in an extremely broad range of wavelengths, 1.15-1.78 μm.

Concepts: Light, Laser, Stimulated emission, Raman scattering, Population inversion, Rayleigh scattering, Active laser medium, Fiber laser