Time-resolved study electronic and thermal contributions to the nonlinear refractive index of Nd3+: SBN laser crystals

The propagation of an optical beam through dielectric media induces changes in the refractive index, An, which causes self-focusing or self-defocusing. In the particular case of ion-doped solids, there are thermal and non-thermal lens effects, where the latter is due to the polarizability difference, Delta alpha, between the excited and ground states, the so-called population lens (PL) effect. PL is a pure electronic contribution to the nonlinearity, while the thermal lens (TL) effect is caused by the conversion of part of the absorbed energy into heat. In time-resolved measurements such as Z-scan and TL transient experiments, it is not easy to separate these two contributions to nonlinear refractive index because they usually have similar response times. In this work, we performed time-resolved measurements using both Z-scan and mode mismatched TL in order to discriminate thermal and electronic contributions to the laser-induced refractive index change of the Nd3+-doped Strontium Barium Niobate (SrxBa1-xNb2O6) laser crystal. Combining numerical simulations with experimental results we could successfully distinguish between the two contributions to An. (C) 2007 Elsevier B.V. All rights reserved.

New laser soldering-based closures: a promising method in natural orifice transluminal endoscopic surgery

Complete closure of gastrotomy is the linchpin of safe natural orifice transgastric endoscopic surgery.

Expanded polytetrafluoroethylene graft for bypass surgery using the excimer laser-assisted nonocclusive anastomosis technique

OBJECT: Patients with complex craniocerebral pathophysiologies such as giant cerebral aneurysms, skull base tumors, and/or carotid artery occlusive disease are candidates for a revascularization procedure to augment or preserve cerebral blood flow. However, the brain is susceptible to ischemia, and therefore the excimer laser-assisted nonocclusive anastomosis (ELANA) technique has been developed to overcome temporary occlusion. Harvesting autologous vessels of reasonable quality, which is necessary for this technique, may at times be problematic or impossible due to the underlying systemic vascular disease. The use of artificial vessels is therefore an alternative graft for revascularization. Note, however, that it is unknown to what degree these grafts are subject to occlusion using the ELANA anastomosis technique. Therefore, the authors studied the ELANA technique in combination with an expanded polytetrafluoroethylene (ePTFE) graft. METHODS: The experimental surgeries involved bypassing the abdominal aorta in the rabbit. Ten rabbits were subjected to operations representing 20 ePTFE graft-ELANA end-to-side anastomoses. Intraoperative blood flow, followup angiograms, and long-term histological characteristics were assessed 75, 125, and 180 days postoperatively. Angiography results proved long-term patency of ePTFE grafts in all animals at all time points studied. Data from the histological analysis showed minimal intimal reaction at the anastomosis site up to 180 days postoperatively. Endothelialization of the ePTFE graft was progressive over time. CONCLUSIONS: The ELANA technique in combination with the ePTFE graft seems to have favorable attributes for end-to-side anastomoses and may be suitable for bypass procedures.

Pilot study of hyperopic LASIK using the solid-state laser technology

Background To evaluate and report the visual, refractive, and aberrometric outcomes of LASIK for the correction of low to moderate hyperopia in a pilot group using a commercially available solid-state laser. Methods Prospective pilot study including 11 consecutive eyes with low to moderate hyperopia of six patients undergoing LASIK surgery using the Pulzar Z1 solid-state laser (CustomVis Laser Pty Ltd., currently CV Laser). Visual, refractive, and aberrometric changes were evaluated. Potential complications were evaluated as well. Mean follow-up time was 6.6 months (range, 3 to 11 months). Results A significant improvement in LogMAR uncorrected distance visual acuity (UDVA) was observed postoperatively (p = 0.01). No significant change was detected in LogMAR corrected distance visual acuity (CDVA) (p = 0.21). Postoperative LogMAR UDVA was 0.1 (about 20/25) or better in ten eyes (90.9 %). Mean overall efficacy and safety indices were 1.03 and 1.12. Postoperatively, no losses of lines of CDVA were observed. Postoperative spherical equivalent was within ±1.00 D in ten eyes (90.9 %). With regard to aberrations, no statistically significant changes were found in higher order and primary coma RMS postoperatively (p ≥ 0.21), and only minimal but statistically significant negativization of primary spherical aberration (p = 0.02) was observed. No severe complications were observed. Conclusion LASIK surgery using the solid-state laser technology seems to be a useful procedure for the correction of low to moderate hyperopia, with minimal induction of higher order aberrations.

Influence of the Difference Between Corneal and Refractive Astigmatism on LASIK Outcomes Using Solid-State Technology

Purpose: To evaluate the influence of the difference between preoperative corneal and refractive astigmatism [ocular residual astigmatism (ORA)] on outcomes obtained after laser in situ keratomileusis (LASIK) surgery for correction of myopic astigmatism using the solid-state laser technology. Methods: One hundred one consecutive eyes with myopia or myopic astigmatism of 55 patients undergoing LASIK surgery using the Pulzar Z1 solid-state laser (CustomVis Laser Pty Ltd, currently CV Laser) were included. Visual and refractive changes at 6 months postoperatively and changes in ORA and anterior corneal astigmatism and posterior corneal astigmatism (PCA) were analyzed. Results: Postoperatively, uncorrected distance visual acuity improved significantly (P < 0.01). Likewise, refractive cylinder magnitude and spherical equivalent were reduced significantly (P < 0.01). In contrast, no significant changes were observed in ORA magnitude (P = 0.81) and anterior corneal astigmatism (P = 0.12). The mean overall efficacy and safety indices were 0.96 and 1.01, respectively. These indices were not correlated with preoperative ORA (r = −0.15, P = 0.15). Furthermore, a significant correlation was found between ORA (r = 0.81, P < 0.01) and PCA postoperatively, but not preoperatively (r = 0.12, P = 0.25). Likewise, a significant correlation of ORA with manifest refraction was only found postoperatively (r = −0.38, P < 0.01). Conclusions: The magnitude of ORA does not seem to be a predictive factor of efficacy and safety of myopic LASIK using a solid-state laser platform. The higher relevance of PCA after surgery in some cases may explain the presence of unexpected astigmatic residual refractive errors.

Profitability analysis of a femtosecond laser system for cataract surgery using a fuzzy logic approach

AIM: To define the financial and management conditions required to introduce a femtosecond laser system for cataract surgery in a clinic using a fuzzy logic approach. METHODS: In the simulation performed in the current study, the costs associated to the acquisition and use of a commercially available femtosecond laser platform for cataract surgery (VICTUS, TECHNOLAS Perfect Vision GmbH, Bausch & Lomb, Munich, Germany) during a period of 5y were considered. A sensitivity analysis was performed considering such costs and the countable amortization of the system during this 5y period. Furthermore, a fuzzy logic analysis was used to obtain an estimation of the money income associated to each femtosecond laser-assisted cataract surgery (G). RESULTS: According to the sensitivity analysis, the femtosecond laser system under evaluation can be profitable if 1400 cataract surgeries are performed per year and if each surgery can be invoiced more than $500. In contrast, the fuzzy logic analysis confirmed that the patient had to pay more per surgery, between $661.8 and $667.4 per surgery, without considering the cost of the intraocular lens (IOL). CONCLUSION: A profitability of femtosecond laser systems for cataract surgery can be obtained after a detailed financial analysis, especially in those centers with large volumes of patients. The cost of the surgery for patients should be adapted to the real flow of patients with the ability of paying a reasonable range of cost.

Perinatal outcomes with laser surgery for twin-twin transfusion syndrome

The aim of this tertiary hospital-based cohort study was to determine and compare perinatal outcome and neonatal morbidities of pregnancies with twin-twin transfusion syndrome (TTTS) before and after the introduction of a treatment program with laser ablation of placental communicating vessels. Twenty-seven pregnancies with Stage II-IV TTTS treated with amnioreduction were identified (amnioreduction group). The data were compared with that obtained from the first 31 pregnancies with Stage II-IV TTTS managed with laser ablation of placental communicating vessels (laser group). Comparisons were made for perinatal survival and neonatal morbidities including abnormalities on brain imaging. The median gestation at therapy was similar between the two groups (20 vs. 21 weeks, p = .24), while the median gestation at delivery was significantly greater in the laser treated group (34 vs. 28 weeks, p = .002). The perinatal survival rate was higher in the laser group (77.4% vs. 59.3%, p = .03). Neonatal morbidities including acute respiratory distress, chronic lung disease, requirement for ventilatory assistance, patent ductus arteriosus, hypotension, and oliguric renal failure had a lower incidence in the laser group. On brain imaging, ischemic brain injury was seen in 12% of the amnioreduction group and none of the laser group of infants (p = .01). In conclusion, these findings indicate that perinatal outcomes are improved with less neonatal morbidity for monochorionic pregnancies with severe TTTS treated by laser ablation of communicating placental vessels when compared to treatment by amnioreduction.

Forces from highly focused laser beams: Modeling, measurement and application to refractive index measurements

The optical forces in optical tweezers can be robustly modeled over a broad range of parameters using generalsed Lorenz–Mie theory. We describe the procedure, and show how the combination of experimental measurement of properties of the trap coupled with computational modeling, can allow unknown parameters of the particle—in this case, the refractive index—to be determined.

Highly refractive index sensitive femtosecond laser inscribed long period gratings

The distinct behaviour of femtosecond laser inscribed long period gratings, with a non-uniform index perturbation within the optical fibre core, has been studied experimentally. The non-uniform laser-induced perturbation results in light coupling from the core mode to a greater number of cladding modes than is the case with their UV laser inscribed counterparts, and this is made evident from the surrounding refractive index (SRI) grating response. Femtosecond inscribed long period gratings are shown to simultaneously couple to multiple sets of cladding modes. A 400μm LPG is shown to result in attenuation peaks that have both blue and red wavelength shifts over a 1250nm to 1700nm wavelength range. This gives rise to SRI sensitivities far greater than anything achievable by monitoring a single attenuation peak. The maximum sensitivity produced by monitoring a single attenuation peak was 1106nm/RIU, whereas monitoring opposing wavelength shifts resulted in a significantly improved sensitivity of 1680nm/RIU. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

Microchanneled chirped fiber Bragg grating formed by femto-second laser aided chemical etching for refractive index and temperature measurements

In this work, a microchanneled chirped fiber Bragg grating (MCFBG) is proposed and fabricated through the femtosecond laser-assisted chemical etching. The microchannel (~550 µm) gives access to the external index liquid, thus inducing refractive index (RI) sensitivity to the structure. In the experiment, the transmission bands induced by the reduced effective index in the microchannel region were used to sense the surrounding RI and temperature changes. The experimental results show good agreement with the theoretical analysis. The proposed MCFBG offers enhanced RI sensitivity without degrading the robustness of the device showing good application potential as bio-chemical sensors.

Optical fiber cavity ring down measurement of refractive index with a microchannel drilled by femtosecond laser

A microchannel was inscribed in the fiber of a ring cavity which was constructed using two 0.1%:99.9% couplers and a 10-m fiber loop. Cavity ring down spectroscopy was used to measure the refractive index (RI) of gels infused into the microchannel. The ring down time discloses a nonlinear increase with respect to RI of the gel and sensitivity up to 300 µs/RI unit and an index resolution of 1.4 × 10 was obtained. © 2009 IEEE.

Microchannelled chirped fibre Bragg grating based refractive index sensor formed by femto-second laser processing and HF-etching

The microchannelled chirped fibre Bragg grating (MCFBG) was fabricated using femtosecond laser processing and HF-etching. Intrinsical refractive-index sensitivity induced by the microchannel makes MCFBGs ideal for biochemical sensing.

Fiber laser incorporating an intracavity micro-channel for refractive index and temperature sensing

In this letter, we present a standard linear cavity fiber laser incorporating a microchannel for refractive index (RI) and temperature sensing. The microchannel of ~6µm width created by femtosecond laser aided chemical etching provides an access to the external liquid; therefore, the laser cavity loss changes with the liquids of different RIs. Thus, at a fixed pump power, the output laser power will vary with the change of RI in the microchannel. The results show that the proposed sensing system has a linear response to both the surrounding medium RI and temperature. The RI sensitivity of the laser system is on the order of 10-3, while the temperature sensitivity is about 0.02 C. Both sensitivities could be further enhanced by employing a more sensitive photodetector and using higher pump power.

Microchanneled chirped fiber Bragg grating formed by femto-second laser aided chemical etching for refractive index and temperature measurements

In this work, a microchanneled chirped fiber Bragg grating (MCFBG) is proposed and fabricated through the femtosecond laser-assisted chemical etching. The microchannel (~550 µm) gives access to the external index liquid, thus inducing refractive index (RI) sensitivity to the structure. In the experiment, the transmission bands induced by the reduced effective index in the microchannel region were used to sense the surrounding RI and temperature changes. The experimental results show good agreement with the theoretical analysis. The proposed MCFBG offers enhanced RI sensitivity without degrading the robustness of the device showing good application potential as bio-chemical sensors.