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In this study, we demonstrate the design of a photonic crystal fiber (PCF)-based plasmonic sensor to measure the glucose level of urine. The sensor is designed by placing a small segment of PCF between a lead-in and a lead-out single-mode fiber. We utilize the finite element method to simulate the proposed plasmonic sensor for the measurement of glucose level in urine. To offer external sensing, the cladding layer of the PCF was coated by a thin layer of gold where the gold-coated PCF was immersed in the urine sample. As a result, the urine can easily interact with the plasmonic layer of the sensor. In the outermost laser of the PCF, we considered a perfectly matched layer as a boundary condition. The simulation results confirm excellent wavelength and amplitude sensitivities where the maximum wavelength sensitivity was 2500 nm/RIU and amplitude sensitivity was 152 RIU−1 with a sensing resolution of 4 × 10−6. For optimization of the plasmonic sensor, we varied the physical parameters of the cladding air holes and the thickness of the gold layer during the simulation. We strongly believe that the proposed plasmonic sensor will play a significant role to pave the way for achieving a simple but effective PCF-based glucose sensor.

We have proposed a multimode-fiber identical weak FBG array interrogation based on resonance frequency mapping (RFM). We fabricated five identical weak FBGs in the graded-index fused silica fiber with intervals of approximately 1 m and then multiplexed all of them based on RFM successfully.

Corrosion of nitinol (NiTi) is a major factor in the failure of implantable materials. Recently, as the importance of corrosion of metals has increased, testing according to international guidelines is essential. The purpose of this study was to evaluate the corrosion resistance of NiTi wire through heat treatment and passivation process. In this study, NiTi wire used two commercially available products and a self-manufactured stent. Experimental consideration was carried out according to ASTM standards. Heat treatment was carried out in an air or a salt furnace, and the corrosion was measured after additional process, such as passivation and scratch tests. As a result, the metal potential was rapidly decreased in the air furnace group. On the other hand, the potential of wires was dramatically increased in the salt furnace group compared to the air furnace group. The dislocation decreased below the acceptance criteria (>600 mV) within 60 s of heat treatment time in the air furnace. Moreover, the potential was dramatically improved, even after only 20 min of passivation treatment (1076 mV, 442% compared to the non-passivated group), and it continued to rise until 180 min. This phenomenon was similarly observed in the group of self-manufactured stents. The potential slightly decreased by the scratch process (93.1%) was significantly reduced by the air furnace process (315 mV, 24.4% of the nontreated group). In the passivated group of the air furnace sample with reduced potential, the potential was restored to the level before the air furnace (scratch stage) (1032 mV). In conclusion, the heat treatment is preferably carried out in a salt furnace rather than an air furnace, and the passivation process can be an advantageous tool to improve corrosion resistance by suppressing the oxidation process.

This paper demonstrates the formation of high-fill-factor plano-convex cylindrical and dome-type micro-lens arrays on fused silica glass surface using CO2 laser assisted reshaping technique. Cylindrical micro-lens array is fabricated by polishing the femtosecond laser engraved linear micro-gratings by a CO2 laser beam. Initially, a femtosecond laser beam has been irradiated on the surface of the fused silica glass samples to fabricate periodic micro-gratings on the glass surface. Afterwards, these micro-gratings encoded glass samples are polished several times by a CO2 laser beam. As a result, plano-convex cylindrical micro-lens arrays with the lens period varying from 20 μm to 50 μm are developed on the glass surface. Similarly, dome-type micro-lens array is achieved by femtosecond laser assisted fabrication of periodic micro-pillars followed by several times CO2 laser polishing. We report the formation of a large variety of dome-shape micro-lens array with lens size varying from 20 μm × 20 μm to 50 μm × 50 μm. The fabricated micro-lenses show great consistency in size and shape throughout the sample area. We also investigate the intensity distribution of light passed through the micro-lens engraved glass samples. Using the dome-type micro-lens array engraved glass samples, a Gaussian laser beam has been converted to a flat-top laser beam for selective patterning of a thin indium-tin-oxide coating from fused silica glass surface.

Our study proposes a technique to enhance light extraction efficiency of light emitting diodes (LEDs) by incorporating various micro-/nanolens arrays (MNLAs) on the substrate layer, which in turn increases the external quantum efficiency (EQE) of the LEDs. To simulate the LEDs, we utilized the finite difference time domain method. To achieve a white LED, we inserted a thin layer of NiO at the interface between the n-type ZnO and the p-type GaN. The basic n-ZnO/NiO/p-GaN heterojunction-based LED exhibited an EQE of 10.99% where the effective refractive index of the LED structure was 1.48. The EQE was further increased by engraving various planoconvex or planoconcave MNLA on the top surface of the substrate layer. A maximum EQE of 12.4% was achieved for convex-1 type (lens height of 0.5 μm and radius of 0.4 μm) elliptical lens engraved LED where the effective refractive index was 1.4. In addition, the peak electroluminescence (EL) light intensity of convex-1 lens-based LED was twice than the light intensity observed in basic LED. Because of excellent EL spectrum and significant amount of light throughout the visible spectrum, the proposed convex-1 structure-based LED can be considered as a prospective candidate for white LED.

We demonstrate a technique for fabricating microstrip patch antennas using femtosecond laser patterning followed by ultraviolet beam and chemical treatment. Initially, we design the physical parameters of both single-slot and double-slot microstrip patch antennas and simulate them using high-frequency structure simulator for optimization. Simulation results exhibit a return loss of −26 dB at the resonant frequency of 22.9 gigahertz (GHz) for single-slot microstrip patch antenna and −18.3 dB at 24.03 GHz for double-slot microstrip patch antenna. The three-dimensional polar plot and far-field radiation pattern of the microstrip patch antennas confirm excellent directivity of the antennas. Furthermore, we investigate the return loss of the fabricated microstrip patch antennas. For single-slot microstrip patch antenna, experimental result shows a return loss of −21.25 dB at 22.7 GHz. In contrast, double-slot microstrip patch antenna shows a return loss of −27 dB at 24.1 GHz. In addition, we compare the performance of the double-slot microstrip patch antenna fabricated using femtosecond laser-assisted technique and photolithographic technique and find better performance in the femtosecond laser-fabricated microstrip antenna. The proposed femtosecond laser-based technique is simple and shows promises in precise fabrication of high-quality microstrip antennas.

This article demonstrates three-dimensional (3D) hologram printing in polymethyl methacrylate (PMMA) and linthum niobate (LiNbO 3 ) samples by means of single beam femtosecond laser direct writing technique. We have printed double-layer 3D hologram, having a background and foreground layer, inside PMMA substrate. Triple-layer 3D hologram, comprising a background, middle, and foreground layer, has been fabricated inside LiNbO3 sample. In both cases, each layer is superimposed over the bottom layers of the holograms. The 3D holograms consist of images (in our case, letters) printed in multiple layers so that each layer is alternately visible depending upon the angle of perspective of the observer. Initially, the target image is converted to an equivalent image by a set of periodic micro-metric lines. Afterwards, using femtosecond laser irradiation a set of periodic diffraction gratings have been fabricated in lieu of micro-lines to form the images in multiple layers, where the orientation of the diffraction gratings is different in different layers. As a result, the 3D holograms display a distinctive multi-color effect.

This paper demonstrates the design and development of a synchronized femtosecond laser pulse switching system and its applications in nano-patterning of transparent materials. Due to synchronization, we are able to control the location of each irradiated laser pulse in any kind of substrate. The control over the scanning speed and scanning step of the laser beam enables us to pattern periodic micro/nano-metric holes, voids, and/or lines in various materials. Using the synchronized laser system, we pattern synchronized nano-holes on the surface of and inside various transparent materials including fused silica glass and polymethyl methacrylate to replicate any image or pattern on the surface of or inside (transparent) materials. We also investigate the application areas of the proposed synchronized femtosecond laser pulse switching system in a diverse field of science and technology, especially in optical memory, color marking, and synchronized micro/nano-scale patterning of materials.

We report on fabricating high-fill-factor plano-convex spherical and square micro-lens arrays on fused silica glass surface by using a CO2 laser-assisted reshaping technique. Initially, periodic micro-pillars are encoded on glass surfaces by means of a femtosecond laser beam, afterwards, the micro-pillars are polished several times by irradiating a CO2 laser beam on top of the micro-pillars. Consequently, a spherical micro-lens array with micro-lens size of 50 μm × 50 μm and a square micro-lens array with micro-lens size of 100 μm × 100 μm are formed on the surface of the fused silica glass. We also study the intensity distribution of light passing through the glass sample engraved with a spherical micro-lens array. The simulation result shows that the focal length of the spherical micro-lens array is 35 μm. Furthermore, we investigate the optical properties of glass samples with engraved micro-lens arrays. The proposed CO2-laser-based reshaping technique is simple and fast and shows promises for fabricating arrays of smooth micro-lenses in various transparent materials.

The objective of this study was to evaluate the viability of tumor cells after laser ablation for papillary thyroid carcinoma and to determine if the laser ablation procedure using multidirectional-firing fiber had a therapeutic effect.Many noninvasive techniques have been introduced for the treatment of thyroid cancer. Among them, the laser ablation technique has been proven its therapeutic effect for large benign thyroid nodules.Three patients who were diagnosed with papillary thyroid carcinoma using fine-needle aspiration cytology were enrolled. All of the selected tumors were2 cm in size and there was no case of extrathyroidal extension. A laser fiber was inserted into the tumor by means of ultrasound guidance and ablation was performed for 3 min at 7 W of output power. The specimens were stained using hematoxylin and eosin (HE) and nicotinamide adenine dinucleotide (NADH), and were evaluated by a pathologist.The specimen showed three clearly distinct zones: zone 1, carbonized zone; zone 2, coagulated zone; and zone 3, normal thyroid tissue. No remaining thyroid tissue was visible in zone 1 after staining, because of complete necrosis of the tumor cells. Although thyroid tissue remained in zone 2, no viable tumor cells were detected using NADH staining.It was found that laser ablation using multidirectional-firing fiber could be an effective treatment technique for papillary thyroid carcinoma. This technique enables not only direct cancer treatment with cell necrosis but also the securement of a tumor safety margin in a similar manner to surgery.

We demonstrate the characteristics of terahertz (THz) wave modulation by 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) thin films deposited on silicon substrates patterned with one-dimensional periodic multi-channels. The polarization independence of the THz wave modulation in the hybrid structures with one-dimensional channels indicates that the rapid in-plane diffusion of the carriers injected into the TIPS pentacene thin films plays an important role in the high modulation of THz waves. Understanding the mechanisms of THz modulation is important for optimizing the performance of THz devices based on organic/inorganic hybrid structures.

This paper demonstrates the laser assisted formation of plano-convex cylindrical and flat-top curved micro-lens array on fused silica glass surface. Initially, femtosecond laser pulses are irradiated on the sample glass to fabricate periodic linear micro-gratings on the glass surface. Afterwards, we reshape the micro-gratings by several times irradiation of a CO 2 laser beam by focusing the laser beam on top of the micro-gratings. As a consequence, plano-convex cylindrical micro-lens array with a period varying from 20 to 40 µm are formed on fused silica glass surface. However, flat-top curved gratings’ array is observed on the glass surface for a gratings’ period of 50 µm. The fabricated micro-lenses show great consistency in size and shape throughout the sample area. Furthermore, we analyze the formation mechanism of micro-lens array on glass surface using the CO 2 laser assisted reshaping technique. The proposed reshaping technique exhibits great potential for forming a large variety of micro-lens arrays on the surface of various transparent materials.

Finding ways to pattern indium-tin-oxide (ITO) thin films attached with flexible polymer plays an important role in manufacturing a large variety of photonic/optical devices including flexible display panels. This paper demonstrates femtosecond laser assisted selective removal of a thin layer of ITO coating deposited on a flexible polymer substrate. We utilize both flat-top and Gaussian shape beams to pattern micro/nano-metric grooves on ITO thin films disallowing any damage on the polymer substrate. The flat-top beam enables us to print rectangular profile grooves on ITO-coated polymer substrate. We also investigate the influence of objective lens and galvanometer scanner on the size and shape of the grooves on ITO thin films. Furthermore, we determine the ablation thresholds for selective patterning of ITO coating under various irradiation conditions. In addition, we achieved nano-grooves of width down to 570 nm, which has been reported for the first time in this paper. The engraved micro/nano-scale grooves on OTO thin films show excellent electrical isolation from the remaining ITO thin film. The femtosecond laser assisted fabrication technology exhibits a unique scheme for machining numerous patterns on ITO thin films with great flexibility.

The optical fiber probe consisted of a lensed fiber is analyzed and experimentally characterized. The working distance and spot size of the probe could be simultaneously controlled by taking a proper combination of input parameters.

A laser-induced intense Ka hard X-ray source was developed by using a novel copper film target and a 27-TW femtosecond laser system. A specially designed pinhole camera was employed to measure the X-ray photon flux, X-ray energy spectrum, and X-ray source image. By adapting a single photon counting method, we estimated the photon number in the full width at half maximum (FWHM) spectral region to be 1.74 × 109 photons/sr for 8.05-keV Cu Ka X-rays. The shape of the X-ray source was matched well with that of the focused laser beam on the target. By provision of a lengthy copper film of 50 m with a thickness of 50 µm, the novel copper film target is capable of long time operation of more than 27 hours at a repetition rate of 10 Hz. The hard X-ray source is suitable for applications in single-shot X-ray contrast imaging or in ultrafast pump-probe analyses of material structures.

This paper reports the fabrication of various micro-lensed single-mode optical fibers through the use of an enhanced peak power $CO_2$ laser beam. The end faces of the optical fibers are exposed to the $CO_2$ laser beam to form convex, concave, and conical shape optical fiber tips. Peak power of the $CO_2$ laser beam was varied from 0.8 W to 1.5 W depending on the shape of the optical fiber tip. We also discover the dependence of the angle of the optical fiber tip on the rotation angle and the number of $CO_2$ laser irradiations. The angle shows an increasing trend with both these parameters. We achieve a wide range of lenticular fibers with end face angle varying from $4.47^{\circ}$ to $8.13^{\circ}$ . Furthermore, we investigate the emission pattern of light from the developed micro-lensed fibers. The proposed $CO_2$ laser based optical fiber reshaping technique shows great consistency, and thus is suitable for commercial applications.

We have fabricated double-layer diffraction gratings with a zigzag shape inside fused silica glass by using a femtosecond laser, the intention of which is to overcome the hindrance of shortening grating’s period. Our primary focus is to utilize double-layer gratings to achieve a diffraction pattern similar to that from a single-layer diffraction grating with the same period as the double-layer grating. We fabricated two kinds of double-layer gratings, where the grating’s period was either 6 μm or 2 μm for both layers. The first set of diffraction gratings was printed 70 μm inside the glass substrates. This layer was followed by the second layer grating engraved just below the first layer grating (The shifted grating’s position was shifted to the right by 3 μm for the 6-μm-period grating and by 1 μm for the 2-μm-period grating). By varying the layer gap, we have found the optimal position (layer gap: 500 nm) to achieve a diffraction pattern similar to that of a single-layer diffraction grating with half the grating’s period of the double-layer gratings.

This research demonstrates laser-assisted fabrication of high-efficiency diffraction gratings in fused-silica glass samples. Initially, femtosecond laser pulses are used to engrave diffraction gratings on the glass surfaces. Then, these micro-patterned glass samples undergo CO2 laser polishing process. unpolished diffraction gratings encoded in the glass samples show an overall diffraction efficiency of 18.1%. diffraction gratings imprinted on the glass samples and then polished four times by using a CO2 laser beam attain a diffraction efficiency of 32.7%. We also investigate the diffraction patterns of the diffraction gratings encoded on fused-silica glass surfaces. The proposed CO2 laser polishing technique shows great potential in patterning high-efficiency diffraction gratings on the surfaces of various transparent materials.

In this paper, using the value theoretically calculated to emit multidirectionally a beam coming into an optical fiber with diameter of 125 μm, we modeled and produced a cone-shaped structure at the distal end of the fiber. A numerical simulation was performed for an optical fiber tip in which all incident beams were totally reflected and emitted toward the side, as well as for an optical fiber tip from which the beams could be emitted forward and sideways simultaneously. We produced multidirectional-firing optical fiber tips based on the simulation result and model. Laser fabrication of the optical fiber was done by processing a cone-shaped structure at the distal end of an optical fiber with diameter of 125 μm using a femtosecond pulsed laser and polishing the processed surface with a CO2 laser. We also conducted an analysis to compare experimental and simulation results.

*1 Electronics and Communication Engineering Discipline, School of Science, Engineering and Technology, Khulna University, Khulna 9208, Bangladesh *2 R&D Center, Samsung Corning Precision Materials, 1320-10 Seocho-dong, Seocho-gu, Seoul, Republic of Korea. *3 Advanced Photonics Research Institute (APRI), Gwangju Institute of Science and Technology (GIST), 1 Oryong-dong, Buk-gu, Gwangju 500-712, Republic of Korea *4 Department of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701, Republic of Korea E-mail: shamim@kaist.ac.kr

Laser-assisted endoscopic surgery is made possible by employing optical devices such as fiber optics and hollow wave-guides. In some applications of laser-assisted endoscopic surgery, it is necessary to change the direction of the light emission. Our group reported a new fabrication method for bi-directional firing fibers. The conical surface of the fiber tip made the bi-directional emission of the laser light at the distal end of the fiber. In this study, we employed the bi-directional firing fiber for laser-assisted coagulation of soft tissue. The developed fiber and the normal forward-firing fiber are used for the endoscopic delivery system of a continuous IR laser into an in vitro porcine liver. The ablation and coagulation pattern were compared for two distinctive fiber systems. Regardless of the laser's parameters, the bi-directional firing fiber produced a cavity and coagulation zone with more or less a circular shape, while the forward fiber produced an elongated cavity and coagulation region. The bi-directional firing fiber produced wider and shorter coagulation and cavity zones compared to that of the forward-firing fiber. We expect the bi-directional firing fiber to be an excellent optical delivery system for endoscopic laser-hyperthermia when used against various tumors in the liver, breast and thyroid.

We demonstrate the design and simulation of intense light beam (ILB) achieved by concave microlens engraved lenticular fibers. Both single and multiple microlenses of spherical and elliptical shapes have been incorporated just inside the fiber core. The ILBs have been designed using commercial OptiFDTD simulator. We investigate the average light intensity and beam profile at several locations including near field, far field-1, and far field-2 after the end face of the optical fibers. For single microlens, elliptical-shaped microlens engraved optical fibers show higher light intensity compared to spherical-shaped microlens engraved fibers. Light intensity at the output of the single-microlens incorporated fibers shows increasing trend with the increase of the radius of curvature (R) of the microlenses, where the highest light intensity has been achieved for R = − 17.65 μm. For microlens array engraved lenticular fibers, 9-lens model having R = − 8 μm has shown the highest light intensity. Due to the interference of light coming out from neighbor microlenses, the diffraction pattern, i.e., beam profile at any particular plane, is different for different arrangements of the microlenses. The proposed lenticular fibers are expected to have a wide range of applications in micro-optical systems, especially in biomedical engineering.

Currently, various optical fiber tips are used to deliver laser beam for endoscopic surgery. In this paper, we demonstrated multidirectional (forward and side) firing optical fiber tip using a femtosecond micromachining and laser polishing technology. We controlled the edge width of optical fiber tip, by modulating the condition of laser, to regulate the amount of side and forward emission. The distal end of the optical fiber with core/clad diameter of was microstructured with cone shape by using a femtosecond laser. And then the microstructured optical fiber tip was polished by laser beam result in smoothing and specular reflection at the surface of the cone structure. Finally, we operated the LightTools simulation and good agreement was generally found between the proposed model and experimental simulation.

In this work, we report the progressive formation of first nanoparticles, next fine ripples, and eventually coarse ripples during the irradiation of single-crystal 6H-SiC surfaces with increasing number of femtosecond laser pulses (λ = 515 nm, τ = 250 fs, repetition rate = 100 kHz). At laser fluences greater than the single-pulse ablation threshold, nanoparticles were produced on the surface by the first few pulses over which fine ripple patterns overlapped at increased pulse numbers. As the pulse number was further increased over ten, the surface was gradually transformed into a coarse ripple–covered one. At laser fluence below the threshold, however, only fine ripples were formed nonuniformly.

We investigated transmission characteristics of folded slot resonators on a free-standing thin stainless steel film in terahertz frequency. The transmission at the resonance determined by the length of the slot was roughly proportional to the cosine function of the angle between directions of the slot and the polarization of incident light. Generally, the transmission at the resonance in the folded slot resonators was higher than that of a straight slot. Especially, the transmission efficiency at the 60° angle in the folded slot was three times higher than that in the straight slot. This is caused by strong oscillations of the accumulated charges inside the internal area formed by two arms of the folded slot. This finding demonstrates a new method for designing compact structures based on the folded geometry and for realizing THz devices.

To achieve excellent biocompatibility of metal-based implants, hydroxyapatite thin film coatings on nanotube-formed Ti–35Nb–10Zr alloys after femtosecond laser texturing have been investigated. Three groups of samples were prepared: (1) microtextured surfaces using femtosecond (FS) laser, (2) nanotube surfaces formed by anodization, and (3) hydroxyapatite coatings vapor-deposited by a physical electron beam method on the Ti–35Nb–10Zr ternary alloy. The surface morphology of the Ti–35Nb–10Zr alloys was examined by x-ray diffractometry, field-emission scanning electron microscopy, and energy-dispersive x-ray spectroscopy. To investigate ion release, potentiodynamic polarization testing was carried out in 0.9%NaCl solution, and wettability tests and MG 63 osteoblast-like cell culture studies were performed on the surfaces of the three groups to evaluate contact angle and cell growth morphology, respectively. The Ti–35Nb–10Zr alloys exhibited the equiaxed β phase structure. The FS laser-treated Ti–35Nb–10Zr alloys showed circular traces with diameters of 28 ± 1.5 μm and hole separations of 50 μm, and the nanotubes formed on the surfaces had diameters of 180 ± 15 nm and compositions consistent with TiO 2 , Nb 2 O 5 , and ZrO 2 . The nanotube structure showed anatase, rutile and β-titanium diffraction peaks, whereas the HA-coated surface on the nanotubes showed hydroxyapatite, anatase and rutile peaks. The HA coatings displayed the desired role of decreasing the metal ion release with a lower current density value, and the nanotubes and FS laser-treated surface showed wider passive regions compared to other surfaces. The HA-coated surface on the nanotubes after FS laser texturing showed the lowest contact angle compared with the other surfaces. From FE-SEM observations, cell attachment and spreading of MG 63 cells showed significantly higher tendency for surfaces covered by HA coating and nanotubes.

This paper demonstrates the design of high efficiency OLEDs by incorporating micro/nano-metric structures on the surface of and inside the substrate layer of the OLEDs. The OLEDs have been designed and simulated using Lumerical FDTD simulator. We also analyze the performance of the OLEDs from various perspectives such as quantum efficiency, normalized transmitted power, intensity, and angular distribution of light. To increase light extraction from the substrate layer, various micro/nano-metric structures, made of SijN 4 , have been incorporated as light scattering structures. Single layer structures of various size, shape (plano-convex & plano-concave lenses and pillars), and period have been investigated during our simulation. Simulation results confirm higher light extraction, angular distribution, and efficiency in micro/nano-metric structures induced OLEDs, compared to traditional OLEDs. Plano-concave MLA engraved OLEDs show high out-coupling efficiency, whereas, nano-pillars engraved OLED shows consistent light distribution in a wide angular region. We strongly believe that, the proposed OLEDs will have wide range of commercial applications.

We demonstrate self-fabrication of void arrays in a fused silica transparent in the visible and a color-filter borosilicate glass strongly absorptive at 800 nm using tightly focused Ti-sapphire femtosecond laser pulses at 1 kHz without scanning. The period, the size, the number of voids, and the length of the aligned void structure were controlled by changing the laser pulse energy, and the position of the focal point inside two materials. The void arrays were observed by an optical microscope and also estimated by an optical diffraction experiment. The void size and period were smaller in the absorptive glass than in the transparent glass. The submicrometer-sized void was observed by a scanning electron microscope. The smaller and clearer void arrays were formed in the color filter than the fused silica glass. With increasing the laser focal depth, the void-array length increased in the fused silica and decreased in the color filter.

A femtosecond laser has been used to produce spatially confined micromachining on mold stainless steel STAVAX. We investigated femtosecond laser-induced line structuring on mold stainless steel STAVAX using the laser scanning mode with various scanning speeds, various fluences and two polarization configurations. The damage threshold fluence of single pulse irradiation (Fth) was measured to be about 80 mJ/cm2. The damage threshold fluence of the scanning mode was approximately identical (0.75 Fth∼1.25 Fth) to that of the single pulse irradiation. However, a fluence of 2.50 Fth was necessary to induce continuous line structures for high scanning speeds and a fluence of 1.25 Fth was required to induce continuous line structures for low scanning speeds. The width of laser-machined lines increased with the irradiation fluence and decreased with the scanning speed regardless of the polarization configuration. The formation of laser-induced periodic structures (termed “ripple”) was examined using various laser parameters. It was clear that the formation of the ripple was governed by the irradiation fluence and the scanning speed of the beam. We were able to produce nano-scale structures in large areas by employing multiple line irradiations with the laser beam.

A double lambda four-level system could be implemented with biexcitonic transitions on GaAs quantum well. We observed that the phase dependent biexcitonic transition could be explained by interference between one-photon and three-photon transition in a double lambda four-level system. An ultralow-light switch pulse could control 80% of biexcitonic absorption, which demonstrated all-optical switching with biexcitonic double lambda system.

A method for adjusting the working distance and spot size of a fiber probe while suppressing or enhancing the back-coupling to the lead-in fiber is presented. As the optical fiber probe, a lensed optical fiber (LOF) was made by splicing a short piece of coreless silica fiber (CSF) on a single-mode fiber and forming a lens at the end of the CSF. By controlling the length of the CSF and the radius of lens curvature, the optical properties of the LOF were adjusted. The evolution of the beam in the LOF was analyzed by using the Gaussian ABCD matrix method. To confirm the idea experimentally, 17 LOF samples were fabricated and analyzed theoretically and also experimentally. The results show that it is feasible in designing the LOF to be more suitable for specific or dedicated applications. Applications in physical sensing and biomedical imaging fields are expected.

The fabrication of parallel deep nanogrooves on 6H-SiC by femtosecond laser ablation (λ=785 nm) is reported. The periodicity of the nanogrooves was measured to be about 200±20 nm and the depth exceeded 15 μm. The nanogrooves have high uniformity in size and pattern over the entire depth. Laser fluence is found to be the critical parameter to obtain these deep and regular nanogrooves. The feasibility for large area fabrication of nanogrooves by femtosecond laser ablation is demonstrated.

The self-organized formation of ripples in the direction parallel to the groove during the femtosecond laser machining of microgrooves on aluminum nitride ceramic at laser fluences much higher than the single-pulse ablation threshold is reported. These parallel ripples are notably different from the commonly observed polarization-perpendicular ripples and are produced in grooves having an appropriate width and depth, irrespective of laser polarization. From subsequent experiments with narrow and wide groove widths, it could be considered that the groove walls play an important role in the formation of these parallel ripples, possibly by confining the laser-induced plasma.

We report femtosecond laser bonding with strengths of a few MPa and the material mixing during the laser bonding process by using Sm3+- and Cr3+-doped glasses and 180 fs pulses at a repetition rate of 1 kHz from an amplified Ti:sapphire laser at a wavelength of 785 nm. By analyzing fluorescence spectra taken around the interface using a confocal scanning microscope we observed the migration of Sm ions from the upper Sm-doped glass to the lower Cr-doped glass and the reduction from Sm3+ to Sm2+ ions just above the interface for the borate-borate material system. However, in Sm-doped borate-borosilicate, the laser bonding did not produce any reduction and migration of Sm3+ ions.

Femtosecond laser ablation of aluminum oxide (Al2O3) and aluminum nitride (AlN) ceramics was performed under normal atmospheric conditions (λ = 785 nm, τp = 185 fs, repetition rate = 1 kHz), and threshold laser fluencies for single- and multi-pulse ablation were determined. The ablation characteristics of the two ceramics showed similar trends except for surface morphologies, which revealed virtually no melting in Al2O3 but clear evidence of melting for AlN. Based on subsequent X-ray photoelectron spectroscopy (XPS) analyses, the chemistry of these ceramics appeared to remain the same before and after femtosecond laser ablation.