Optical Delivery System Research Articles

Efficiency Analysis of Near Field Optical Transducer Used in Heat-Assisted Magnetic Recording

For heat-assisted magnetic recording system, the efficiency of the optical energy delivery system is important for its application. It affects not only the requirement to laser source output power, but also the heat-assisted magnetic recording (HAMR) head performance and reliability. In this paper, the key factor caused the low efficiency of the near field optical transducer is studied. The results show that the main reason is the longitudinal polarization of the transducer radiation. Large permittivity difference between recording layer and air gap makes large electric field intensity difference within recording layer and air gap. Due to small electric field coupling from air to recording layer, large percentage of the incident power is reflected, absorbed or scattered by other components. The investigation results for power dissipation distributions show that the largest portion of power dissipation is reflection. Reusing the reflected power will be an effective way to improve whole optical system efficiency. Simulation results show that more than 30% increase of the efficiency can be obtained by reusing the reflected power.

All solid-state high power microwave source with high repetition frequency

An all solid-state, megawatt-class high power microwave system featuring a silicon carbide (SiC) photoconductive semiconductor switch (PCSS) and a ferrimagnetic-based, coaxial nonlinear transmission line (NLTL) is presented. A 1.62 cm(2), 50 kV 4H-SiC PCSS is hard-switched to produce electrical pulses with 7 ns full width-half max (FWHM) pulse widths at 2 ns risetimes in single shot and burst-mode operation. The PCSS resistance drops to sub-ohm when illuminated with approximately 3 mJ of laser energy at 355 nm (tripled Nd:YAG) in a single pulse. Utilizing a fiber optic based optical delivery system, a laser pulse train of four 7 ns (FWHM) signals was generated at 65 MHz repetition frequency. The resulting electrical pulse train from the PCSS closely follows the optical input and is utilized to feed the NLTL generating microwave pulses with a base microwave-frequency of about 2.1 GHz at 65 MHz pulse repetition frequency (prf). Under typical experimental conditions, the NLTL produces sharpened output risetimes of 120 ps and microwave oscillations at 2-4 GHz that are generated due to damped gyromagnetic precession of the ferrimagnetic material's axially pre-biased magnetic moments. The complete system is discussed in detail with its output matched into 50 Ω, and results covering MHz-prf in burst-mode operation as well as frequency agility in single shot operation are discussed.

Photoactivation of neurons by laser-generated local heating.

We present a method for achieving temporally and spatially precise photoactivation of neurons without the need for genetic expression of photosensitive proteins. Our method depends upon conduction of thermal energy via absorption by chemically inert carbon particles and does not require the presence of voltage-gated channels to create transmembrane currents. We demonstrate photothermal initiation of action potentials in Hirudo verbana neurons within an intact ganglion and of transmembrane currents in Xenopus oocytes. Thermal energy is delivered by focused 50 ms, 650 nm laser pulses with total pulse energies between 250 and 3500 μJ. We document an optical delivery system for targeting specific neurons that can be expanded for multiple target sites. Our method achieves photoactivation reliably (70 - 90% of attempts) and can issue multiple pulses (6-9) with minimal changes to cellular properties as measured by intracellular recording. Direct photoactivation presents a significant step towards all-optical analysis of neural circuits in animals such as Hirudo verbana where genetic expression of photosensitive compounds is not feasible.

Investigation of the Dynamic Characteristics of Light Delivery for Thermal Assisted Magnetic Recording

Several new technologies have recently been proposed for high areal density greater than 5 Tb/in2 as next generation storage devices. Among these technologies is thermal assisted magnetic recording (TAMR). However, there are several dynamic and realistic problems associated with the current method of TAMR light delivery that must be resolved. In this paper, we investigate and discuss the dynamic characteristics for two kinds of light delivery systems using experimental and simulated results. We concluded that the optical fiber TAMR light delivery system had higher vertical and pitch stiffness. This could result in higher flying height modulation (FHM) on the disk surface and reduced TD-TO performance. Furthermore, since the optical fiber TAMR light delivery system has a lower positive pitch angle during unloading process, as soon as the air bearing disappears after the limiter is engaged, the contact possibility between the slider and the disk increases in unloading process. In addition, for the mounted laser diode (LD) TAMR light delivery system, we constructed a thermal-structural coupling finite element (FE) model of the entire TAMR system and simulated the thermal distribution and structural expansion according to temperature distribution. The results showed that the thermal problem was caused by heat produced by the LD, which can affect the head disk interface (HDI) problem in high areal density.

Fiber-coupled laser-driven flyer plates system

A system for the launch of hypervelocity flyer plates has been developed and characterized. Laser-driven flyers were launched from the substrate backed aluminum-alumina-aluminum sandwiched films. A laser-induced plasma is used to drive flyers with typical thickness of 5.5 μm and diameters of less than 1 mm, to achieve velocities of a few km/s. These flyer plates have many applications, from micrometeorite simulation to laser ignition. The flyer plates considered here have up to three layers: an ablation layer, to form plasma; an insulating layer; and a final, thicker layer that forms the final flyer plates. This technique was developed aiming at improving the energy efficiency of the system. The kinetic energy of flyers launched with the additional layer was found to be enhanced by a factor of near 2 (up to 30%). The optical fiber delivery system governs the output spatial profile of the laser spot and power capacity. Moreover, a technique for coupling high-power laser pulses into an optical fiber has been developed. This fiber optic system has been successfully used to launch flyer plates, and the surface finishing quality of the fiber was found to be an important factor. Importantly, measurements of the flyer performance including the mean velocities and planarity were made by an optical time-of-arrival technique using an optical fiber array probe, demonstrating the good planarity of the flyer and the achievable average velocity of 1.7 km/s with approaching 1 mm diameter. Finally, the relationship between flyer velocities and incident laser pulses energy was also investigated.

Fiber-coupled laser-driven flyer plates experiments

A system for the launch of hypervelocity flyer plates is developed, characterized and applied. Laser-driven flyers are launched from substrate backed aluminum-alumina- aluminum sandwiched films. A laser-induced plasma is used to drive flyers with a thicknesses of a 5.5 m and a diameter of less than 1 mm, and typically, the flyer plates can achieve velocities of a few kilometers per second. These flyer plates have several applications ranging from micrometeorite simulation to laser ignition. The flyer plates considered here have three layers: an ablation layer for forming plasma; an insulating layer; and a final thicker layer for forming the final flyer plate. The optical fiber delivery system determines the spatial profile of the laser spot and power capacity. A technique and procedure for coupling high power laser pulse into optical fiber is developed. The surface finish of the fiber is found to be a critical factor. This fiber optic system is successfully used to launch flyer plates. Measurements of the flyer performance including the mean velocities and planarity are made by an optical time-of-arrival (TOA) technique with using an optical fiber array probe. The flyer shows a good planarity and achieves an average velocity of 1.7 km/s. The relationship between flyer velocity and incident laser pulse energy is investigated.

High‐power diode laser use on Fordyce granule excision: a case report

Fordyce granules are conventionally considered to be a developmental oral lesion with a higher incidence in men. To report a clinical case of surgical lip Fordyce granule excision in a 19-year-old male. Fordyce granules were excised using a high-power diode laser (gallium arsenide [GaAs], Diode Vision®, MDL, 10 Dental Laser Unit, GmbH, Lower Saxony, Germany) with wavelength emission at 980 ± 10 nm, in a continuous wave mode, pulse width of 0.5 μs, fiber optic delivery system of 400 μm in diameter, at 2.5 W. Subsequently, low-intensity laser therapy was applied (gallium-aluminum-arsenide [GaAlAs], at 670 nm, 50 mW, at 4 J/cm(2); Dentoflex®, São Paulo, Brazil] in order to stimulate a faster wound tissue-healing process and less postoperative pain and inflammation. The excellent esthetic result demonstrated the effectiveness of both high- and low-intensity laser therapy on the excision of Fordyce granules.

Evaluation of laser cleaning of ancient Greek, Roman and Byzantine coins

AbstractLaser cleaning tests were performed on ancient coins, which belong to the collection of the Numismatic Museum of Athens, Greece. Silver and copper alloy coins with various types of surface corrosion and ground deposits were studied, using Q‐switched (QS), long pulse (LP) and free‐running (FR) Nd:YAG lasers and a range of laser‐pulsing parameters on wet surfaces. A comparison among the different laser types was made, cleaning with an optical fibre delivery system and an optical focusing subassembly, or with the help of x‐y microadjustable stage. It was discovered that the results of laser cleaning was influenced by the type of corrosion and the corrosion products or the ground deposits on the surface of the coins. The results, evaluated by objective and SEM‐EDX observations, indicated that on silver alloy coins, different wavelengths could achieve a successful laser cleaning for several types of corrosion. On the other hand, laser cleaning could result in loss of the original surface in various cases of copper alloy coins, followed by frequent appearance of the oxidation layer underneath and partial removal of corrosion products and ground deposits. The optimum laser cleaning procedure was associated with the different types of coin corrosions. Special emphasis was stressed on the side effects of the procedures and, in particular, on the minimization of any chemical modifications and thermal results induced to the original surface of the coins. Copyright © 2010 John Wiley & Sons, Ltd.

Development of Photoinitiated Nitric Oxide Releasing Polymer Films for Controlled Drug Delivery

Nitric Oxide (NO) is small, free radical gas that has been shown to have a wide variety of physiological functions, including the ability to hinder tumor angiogenesis at high, but non lethal, concentrations [1]. Previous work suggests that if NO could be effectively delivered in vivo to tumors of patients currently undergoing chemotherapy treatments at the appropriate levels, less damaging chemotherapy treatments could be used against cancer [2]. This could increase the overall survivability of cancer patients, especially in those prone to the harmful effects of chemotherapy: children, elderly, and those of weak immune systems. If NO is especially successful at preventing and eliminating tumor growth, angiogenesis, and carcinogenesis the need for stressful chemotherapy treatments could be eliminated altogether. This project is focused on developing novel photosensitive NO donors that can be incorporated into polymeric systems and used in a fiber optic drug delivery system. Development of these NO-releasing polymers will allow continued investigation of NO's role in tumor death by precisely controlling the surface flux of NO that cells are exposed to. Generating specific surface fluxes of NO from polymer films has been demonstrated by using polymer films that contain photoinitiated NO donors [3], prepared by synthesizing S-nitrosothiol (RSNO) derivitized polymer fillers that are blended into hydrophobic polymers and cast into a film. These films generate and sustain a surface flux of NO based on the wavelength and intensity of light used [3]. Polymers releasing NO are more promising as an NO donor than simply injecting NO into samples because they allow for spatial and temporal control of NO delivery. The specific concentration of NO needed to produce desirable effects on tumor cells (i.e., apoptosis) is not known. Data will be presented that show the synthesis and NO-release properties of novel RSNOs based on the nitrosation of benzyl mercaptan thiols. Specifically, UV-Vis spectrum of benzyl mercaptan in toluene and S-nitrosobenzyl mercaptan after the addition of t-butyl nitrite will be presented. We are currently investigating the effects of varying NO-surface fluxes generated from photolytic NO donating polymer films on aortic smooth muscle cell cultures obtained from mice. Once we have established that we can quantitatively determine the effects of different levels of NO on the proliferation of smooth muscle cell cultures, work will begin to apply this methodology and these novel NO-releasing polymeric systems to begin investigating what durations and surface fluxes of NO are necessary to have tumorcidal effects on specific cancer cells.

Development of Photoinitiated Nitric Oxide Releasing Polymer Films for Controlled Drug Delivery

Nitric Oxide (NO) is small, free radical gas that has been shown to have a wide variety of physiological functions, including the ability to hinder tumor angiogenesis at high, but non lethal, concentrations. Previous work suggests that if NO could be effectively delivered in vivo to tumors of patients currently undergoing chemotherapy treatments at the appropriate levels, less damaging chemotherapy treatments could be used against cancer. This could increase the overall survivability of cancer patients, especially in those prone to the harmful effects of chemotherapy: children, elderly, and those of weak immune systems. If NO is especially successful at preventing and eliminating tumor growth, angiogenesis, and carcinogenesis the need for stressful chemotherapy treatments could be eliminated altogether. This project is focused on developing novel photosensitive NO donors that can be incorporated into polymeric systems and used in a fiber optic drug delivery system. Development of these NO-releasing polymers will allow continued investigation of NO's role in tumor death by precisely controlling the surface flux of NO that cells are exposed to. Generating specific surface fluxes of NO from polymer films has been demonstrated by using polymer films that contain photoinitiated NO donors, prepared by synthesizing S-nitrosothiol (RSNO) derivitized polymer fillers that are blended into hydrophobic polymers and cast into a film. These films generate and sustain a surface flux of NO based on the wavelength and intensity of light used. Polymers releasing NO are more promising as an NO donor than simply injecting NO into samples because they allow for spatial and temporal control of NO delivery. The specific concentration of NO needed to produce desirable effects on tumor cells (i.e. apoptosis) is not known. Data will be presented that show the synthesis and NO-release properties of novel RSNOs based on the nitrosation of benzyl mercaptan thiols. Specifically, UV-Vis spectrum of benzyl mercaptan in toluene and S-nitrosobenzyl mercaptan after the addition of t-butyl nitrite will be presented. We are currently investigating the effects of varying NO-surface fluxes generated from photolytic NO donating polymer films on aortic smooth muscle cell cultures obtained from mice. Once we have established that we can quantitatively determine the effects of different levels of NO on the proliferation of smooth muscle cell cultures, work will begin to apply this methodology and these novel NO-releasing polymeric systems to begin investigating what durations and surface fluxes of NO are necessary to have tumorcidal effects on specific cancer cells.

Aplicación de la tecnología láser en las lesiones de genitales

The use of laser applications in urology has undergone significant advances and is now used in a wide variety of procedures. Improvements in types of lasers, the wavelength of energy used, optical fiber delivery systems, precision of laser applications and cost reduction have served to further improve laser technology and extend the potential applications. The different types of lasers available at the present time appear to be an alternative treatment modality with excellent cosmetic and functional results and low morbidity in the treatment of benign, pre-malignant and malignant lesions in the genital area. The objective of this article is to provide an update on the most important clinical and experimental advancements therapeutic applications of lasers in genital lesions.

Optical fiber-based power and data delivery system for high voltage electronic current transformer

This paper describes a prototype power delivery system developed for high voltage electronic current transformer (ECT) that uses laser light to transfer power to and communicates with the primary converter. The design is based on optical-to-electrical power converters, solid-state diode lasers and optical fibers. Command signals are transmitted via the same up-fiber used to send power from secondary power supply to primary converter. The upward data transmission is completed during the brief interruption of power delivery without affecting steady power-supply. A simple comparator added to the primary converter can take the command data. Experimental results show that the fibers can provide reliable up-link for data transmission at 200 kb/s from the secondary to the primary converter. Based on the delivery system, the secondary converter can control three auxiliary channels to provide additional information. These monitoring channels are used in a time-multiplexing mode to provide information about the operation temperature, voltage and current at the remote unit for monitoring the ECT. This preventive maintenance or built-in test can increase reliability by giving early warning for necessary maintenance request.

Optical detection techniques and light delivery with UV LEDs and optical fibres

Following the recent introduction of AlGaN/GaN based ultraviolet Light Emitting Diodes (UV-LEDs) in the 250 nm to 350 nm wavelength region, a wide range of research activities have begun. For example, using the high levels of power of available UV-light, chemical reactions can be stimulated. However, when optical detection techniques are considered, light intensity and wavelength accuracy are more important to achieve low detection limits. Using LED-based light sources in the ultraviolet instead of the classical deuterium, xenon, mercury or metal halide sources is very attractive due to their high power conversion, relatively simple electronic driving circuitry and low power consumption. For both absorption and fluorescence detection, such LEDs and complete detection systems are powerful tools both traditional and new applications in the field and laboratory. In this work, the electrical and optical properties of these new UV-LEDs will be described. Further, the flexibility of using optical fibres for UV-light delivery will be discussed with respect to the available UV-wavelengths and UV-induced damage. To exemplify the potential of UV LEDs, a self correcting fibre optic detection system over the wavelength range 260 and 280 nm, based on such LEDs will be shown. Further, an overview discussing flexible optical fibre UV-light delivery systems will be given and applications for both will be considered.

Performance and accuracy investigations of two Doppler global velocimetry systems applied in parallel

Two Doppler global velocimetry systems were applied in parallel to assess their performance in wind tunnel environments. Both DGV systems were mounted on a common traverse surrounding the glass-walled 1.4 × 1.8 m2 test section of the wind tunnel. The traverse normally supports a three-component forward-scatter laser Doppler velocimetry system. The reproducible tip-vortex flow field generated by the blunt tip of an airfoil was chosen for this investigation and was precisely surveyed by LDA just prior to the DGV measurements. Both DGV systems shared the same continuous wave laser light source, laser frequency monitoring and fibre optic light sheet delivery system. The principal differences between the DGV implementations are with regard to the imaging configuration. One configuration relied on a single camera view that observed three successively operated light sheets. In the second configuration, three camera views simultaneously observed a single light sheet using a four-branch fibre imaging bundle. The imaging bundle system had all three viewpoints in a forward scattering arrangement which increased the scattering efficiency but reduced the frequency shift sensitivity. Since all three light sheet observation components were acquired onto the same image frame, acquisition times could be reduced to a minimum. On the other hand, the triple light sheet–single camera system observed two light sheets in forward scatter and one light sheet in backscatter. Although three separate images had to be recorded in succession, the image quality, spatial resolution and signal-to-noise ratio were superior to the imaging bundle system. Comparison of the DGV data with LDV measurements shows very good agreement to within 1–2 m s−1. The remaining discrepancy has a variety of causes, some are related to the reduced resolving power of the fibre imaging bundle system (graininess, smoothing), exact localization of the receiver head with respect to the scene, laser frequency drift or background influences. The extensive data base available allows a detailed study of the influence of each of these factors.

The future of lasers in urology

The use of laser applications in urology has undergone significant advances over the past 20 years. Laser technology is now used in a wide variety of procedures, and has become the primary treatment modality or standard of care for many urologic conditions. Despite these advances, a number of challenges still face laser utilization in urologic practice. Recent work has illuminated the potential improvement and further optimization of this field. Improvements in types of lasers, the wavelength of energy used, optical fiber delivery systems, precision of laser application and cost reduction have served to further improve laser technology and extend the potential applications.

Mid-IR Germanium Oxide Fibers for Contact Erbium Laser Tissue Ablation in Endoscopic Surgery

Endoscopic surgical applications of erbium lasers have been limited due to the lack of a suitable mid-IR optical fiber delivery system. Germanium oxide fibers are used for noncontact tissue ablation, but are not recommended for contact tissue ablation applications typically required during endoscopic surgery. This study describes the assembly and characterization of hybrid mid-IR fibers consisting of germanium oxide trunk fibers and sapphire fiber tips, and side-firing germanium oxide fibers with either 45deg angled tips or micromirrors. Average powers up to 8.5 W (850 mJ at 10 Hz) and transmission up to 70% was demonstrated through 450-mum-core, 1.5-m-long fibers, sufficient for endoscopic laser ablation of soft and hard tissues in contact mode.

Comparison of germanium oxide fibers with silica and sapphire fiber tips for transmission of erbium: YAG laser radiation

Endoscopic applications of the Erbium:YAG laser have been limited due to the lack of a suitable optical fiber delivery system. The purpose of this study was to compare the transmission of Er:YAG laser radiation through germanium oxide trunk fibers with silica and sapphire fiber tips for potential use in contact tissue ablation during endoscopy. Er:YAG laser radiation with a wavelength of 2.94 microm, pulse length of 300 microseconds, pulse energies from 5 to 1,360 mJ, coupled into pulse repetition rates of 3-10 Hz, was through 1-m-long germanium oxide fibers with either 1-cm-long, 550-microm-diameter silica or sapphire tips. Transmission through the germanium oxide/sapphire fibers measured 65+/-5% compared with 55+/-4% for the germanium oxide/silica fibers (P<0.05). The damage threshold for the hybrid fibers averaged 309+/- 44 mJ and 126+/-43 mJ, respectively (n = 7 fibers each) (P<0.05). The highest pulse energies transmitted through the fibers were 700 mJ and 220 mJ, respectively. Improved index-matching of the trunk fiber and fiber tip at 2.94 microm resulted in higher transmission and damage thresholds for the germanium oxide/sapphire fibers. The germanium oxide/sapphire fiber may represent a promising mid-infrared optical fiber delivery system for use in endoscopic applications of the Er:YAG laser requiring a flexible, biocompatible, and robust fiber delivery system for contact tissue ablation.

Photodynamic Therapy for Urological Malignancies: Past to Current Approaches

Modern PDT for urological tumors is a potentially selective approach in which in situ photosensitization by a nontoxic drug, locally activated by light, generates cytotoxic reactive oxygen species, causing cell death. While urological clinical experience with PDT is largely limited to treatment for superficial bladder cancer, the advent of novel photosensitizers and technologies for treatment planning, light delivery and dosimetry, PDT for prostate and other urological cancers appears increasingly realistic. We reviewed the current literature on PDT for urological tumors, in addition to recent emerging data from our laboratory and elsewhere. Remarkable progress has been made in the field of photochemistry and photobiology. Together with improved optical delivery and imaging systems PDT holds promise as an alternative, minimally invasive and potentially curative treatment for localized solid tumors as well as for palliative treatment for isolated, clinically problematic metastases. Current experience with photodynamic therapy using contemporary photosensitizing agents and light sources is mainly restricted to in vivo experimental models and early phase clinical trails. However, ongoing preclinical work and clinical trials indicate that safer and effective PDT treatments in uro-oncology are imminent.

Therapeutic applications of lasers in urology: an update

There has been renewed interest in the use of lasers for minimally invasive treatment of urologic diseases in recent years. The introduction of more compact, higher power, less expensive and more user-friendly solid-state lasers, such as the holmium:yttrium–aluminum–garnet (YAG), frequency-doubled neodymium:YAG and diode lasers has made the technology more attractive for clinical use. The availability of small, flexible, biocompatible, inexpensive and disposable silica optical fiber delivery systems for use in flexible endoscopes has also promoted the development of new laser procedures. The holmium:YAG laser is currently the workhorse laser in urology since it can be used for multiple soft- and hard-tissue applications, including laser lithotripsy, benign prostate hyperplasia, bladder tumors and strictures. More recently, higher power potassium–titanyl–phosphate lasers have been introduced and show promise for the treatment of benign prostatic hyperplasia. On the horizon, newer and more effective photosensitizing drugs are being tested for potential use in photodynamic therapy of bladder and prostate cancer. Additionally, new experimental lasers such as the erbium:YAG, Thulium and Thulium fiber lasers, may provide more precise incision of soft tissues, more efficient laser lithotripsy and more rapid prostate ablation. This review provides an update on the most important new clinical and experimental therapeutic applications of lasers in urology over the past 5 years.

Adeno-Associated Virus Vectors in Clinical Trials

Adeno-Associated Virus Vectors in Clinical Trials