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Fabrication of millimeter-long structures in sapphire using femtosecond infrared laser pulses and selective etching
摘要： This paper analyzes laser and etching parameters to fabricate open and continuous microchannels and stacks of such microchannels in the bulk of crystalline sapphire (??-Al2O3). The structures are produced using a two-step method consisting of laser irradiation and selective etching. Infrared femtosecond laser pulses are focused in the bulk to locally render the crystalline material into amorphous. The amorphous material is, then, selectively etched in hydrofluoric acid. Amorphous sapphire shows a high etching selectivity in comparison to its crystalline state, which makes this material very attractive for a use with this technique. However, some of its properties make the processing challenging, especially during the laser-induced amorphization phase. This paper studies the effect of laser parameters by a step-by-step approach to fabricate long structures (longest dimensions up to millimeters) of different shapes inside the bulk of sapphire. The minimum cross-sectional dimensions of the resulting structures (microchannels) vary from few hundreds of nanometers for the smallest channels to tens of micrometers for the largest stacks of microchannels. The effect of the variation of repetition rate, pulse energy and channel-to-channel distance on the microchannels and stacks of microchannels is studied. SEM micrographs of polished cross-sections are used for performing a quantitative and qualitative analysis of the morphology of the structures after laser irradiation and, subsequently, after selective wet chemical etching.
关键词： Selective etching,Laser processing,Microchannels,Femtosecond laser,Sapphire
更新于2025-09-23 15:21:01
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Beam optimization in a 25 TW femtosecond laser system for high harmonic generation
摘要： It has been demonstrated in the past that high fluxes of extreme ultraviolet (XUV) light could be obtained by driving high harmonic generation (HHG) with high energy lasers. However, the peak intensity at the focal point of a femtosecond laser with more than 100 mJ can be too high for phase-matched HHG in gases. We propose a method to optimize the spatial profile at focus by adding customized wavefront terms. An XUV pulse energy of 5.6 μJ was obtained from HHG when a larger off-focus spot of a 500 mJ Ti: Sapphire laser beam was applied in an argon gas cell.
关键词： wavefront correction,extreme ultraviolet,femtosecond laser,high harmonic generation,Ti: Sapphire laser
更新于2025-09-23 15:21:01
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A discrete core-shell-like micro-light-emitting diode array grown on sapphire nano-membranes
摘要： A discrete core-shell-like micro-light-emitting diode (micro-LED) array was grown on a 100 nm-thick sapphire nano-membrane array without harmful plasma etching for chip singulation. Due to proper design for the sapphire nano-membrane array, an array of multi-faceted micro-LEDs with size of 4 μm × 16 μm was grown. threading dislocation density in the micro-LeD formed on sapphire nano-membrane was reduced by 59.6% due to the sapphire nano-membranes, which serve as compliant substrates, compared to GaN formed on a planar substrate. Enhancements in internal quantum efficiency by 44% and 3.3 times higher photoluminescence intensity were also observed from it. Cathodoluminescence emission at 435 nm was measured from c-plane multiple quantum wells (MQWs), whereas negligible emissions were detected from semi-polar sidewall facets. A core-shell-like MQWs were formed on all facets, hopefully lowering concentration of non-radiative surface recombination centers and reducing leakage current paths. This study provides an attractive platform for micro-LEDs by using sapphire nano-membrane.
关键词： internal quantum efficiency,photoluminescence,threading dislocation density,micro-LED,sapphire nano-membrane,core-shell-like,cathodoluminescence
更新于2025-09-23 15:21:01
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[Laser Institute of America ICALEO?? 2016: 35th International Congress on Applications of Lasers & Electro-Optics - San Diego, California, USA (October 16a??20, 2016)] International Congress on Applications of Lasers & Electro-Optics - Enhanced drilling of transparent materials with ultrashort pulses
摘要： Ablative processes for transparent materials processing still remains a hot topic, as current techniques still have their limitations in ablation rates and quality, particularly for features on the order of a millimeter or less. In this publication, we present results of recent work on laser micromachining of sapphire with ultrashort pulsed lasers in the sub-picosecond regime. We accomplish this by using bottom-up processing with laser ablation, which has demonstrated the ability to generate zero-taper features with relatively high aspect ratios (>1:1) in many transparent materials. In previous work with <1ps (1030nm) sources, we have demonstrated the ability to drill ≤250μm diameter holes in 430μm thick c-plane sapphire. Here, we extend the scope of this work to examine additional methods and laser parameters presented here. In particular we examine the benefits of frequency conversion to 515nm wavelength, allowing smaller spots and higher fluence levels is compared to trials at the fundamental wavelength. We find no compelling differences in minimum achievable taper or drilling time for processes with 1030nm vs. 515nm performed with similar fluences, but the smaller spot size and increased fluence afforded with 515nm light allows for faster bottom-up drilling. Additionally, we test the effects of water-assisted processing by placing the sapphire wafer in contact with a water bath for better extraction of particulate matter during processing. Processes with a water bath are found to allow holes with 2° taper to be drilled in ≤5 seconds, which is a decrease in cycle time of ≥50% for holes with ≤2° taper in air.
关键词： laser micromachining,bottom-up processing,sapphire,ultrashort pulses,water-assisted processing
更新于2025-09-23 15:21:01
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Development of a continuously tunable titanium-sapphire laser system for the ARIEL laser ion source
摘要： A concept for continuously tunable titanium-sapphire (Ti:Sa) lasers using dispersion prisms is under investigation for the ARIEL (Advanced Rare IsotopE Laboratory) laser ion source at TRIUMF (Canada’s particle accelerator center). Wavelength selection for pulsed Ti:Sa lasers used in hot cavity laser resonance ionization spectroscopy is usually done with birefringent filters (BRFs) and etalons or diffraction gratings. For resonance ionization spectroscopy a laser system allowing a continuous wavelength scan is necessary. Tunable lasers based on BRFs and etalons have high output powers however require synchronized optimization for continuous laser wavelength scans and are therefore laborious to use in scanning applications. Diffraction grating tuned lasers can provide continuous wavelength scan over 200 nm range but typically have lower output laser power due to the grating deformation under high pumping power. Aiming to overcome both shortcomings a laser design based on prisms as dispersing element has been revisited. Simulations on the beam path and optical reflectivity are done which show that these losses can be minimized to around 0.04 % for a tuning range from 700 nm up to 920 nm. Further improvement on the tuning range and reduction on the linewidth will be pursued.
关键词： Titanium-sapphire laser,Tunability,Prisms
更新于2025-09-23 15:21:01
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A direct diode pumped Ti:sapphire laser with single-frequency operation for high resolution spectroscopy
摘要： A direct diode pumped continuous-wave Ti:sapphire laser (DDPTS) is presented. A bow-tie geometry with optical diode is chosen for unidirectional single-mode operation. Frequency selection is performed with a standard combination of birefringent filter and etalon. To accomplish mode-hop free frequency tuning the piezo-driven etalon is stabilized to one of the cavity modes via dither-locking method. To suppress environmental fluctuations the cavity-mode is additionally locked to an external optical cavity with low frequency drift. Feasibility of the setup for high-resolution spectroscopy is demonstrated by saturated absorption spectroscopy of the D2 line of Rubidium.
关键词： Rubidium,Stabilization,Hyperfine structure,Laser,Titanium:sapphire,Optical cavity,Beatnote
更新于2025-09-23 15:21:01
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The CRESST-III low-mass WIMP detector
摘要： The next generation direct dark matter experiment CRESST-III has a high potential to signi?cantly increase the sensitivity to low-mass WIMPs (mχ (cid:46)10 GeV/c2). We present the new CRESST detector module: it consists of a 24 g CaWO4 crystal operated as a phonon detector and a 20x20 mm2 silicon-on-sapphire light detector. The phonon energy threshold is lowered to ～100 eV and a light detector resolution of typically 5 eV is achieved. A fully-scintillating inner detector housing is realised which e?ciently rejects events from surface-alpha decays. The CaWO4 sticks holding the target crystal are also operated as calorimeters to discriminate all possible artefacts related to the support structure. A projection for the sensitivity to spin-independent WIMP-nucleon scattering is given for the ?rst phase of CRESST-III which will start beginning of 2016.
关键词： CaWO4 crystal,dark matter,silicon-on-sapphire light detector,CRESST-III,low-mass WIMPs
更新于2025-09-23 15:21:01
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The efficacy of plasmonic model to calculate HSFL nanostructure period in Sapphire
摘要： In this work, we try to determine all the period of nanostructure subwavelength that can be observed during irradiation by multipulse femtosecond laser in dielectric materials. For this, we use a generalized plasmonic model developed previously to follow the evolution of the periods of the nanostructures on the Sapphire material and their optical properties according to electron-holes plasma excitation and varying the optical spectrum between 300 and 1400 nm. We ?nd a nanostructure area where all the period observed experimentally must be included inside it. This plasmonic model shows its e?ciency and its precision on a nanoscale.
关键词： Sapphire,plasmonic model,HSFL nanostructure,femtosecond laser,electron-holes plasma
更新于2025-09-23 15:19:57
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Ytterbium-doped fibre femtosecond laser offers robust operation with deep and precise microsurgery of C. elegans neurons
摘要： Laser microsurgery is a powerful tool for neurobiology, used to ablate cells and sever neurites in-vivo. We compare a relatively new laser source to two well-established designs. Rare-earth-doped mode-locked fibre lasers that produce high power pulses recently gained popularity for industrial uses. Such systems are manufactured to high standards of robustness and low maintenance requirements typical of solid-state lasers. We demonstrate that an Ytterbium-doped fibre femtosecond laser is comparable in precision to a Ti:Sapphire femtosecond laser (1–2 micrometres), but with added operational reliability. Due to the lower pulse energy required to ablate, it is more precise than a solid-state nanosecond laser. Due to reduced scattering of near infrared light, it can lesion deeper (more than 100 micrometres) in tissue. These advantages are not specific to the model system ablated for our demonstration, namely neurites in the nematode C. elegans, but are applicable to other systems and transparent tissue where a precise micron-resolution dissection is required.
关键词： Ytterbium-doped fibre femtosecond laser,Laser microsurgery,neuronal regeneration,Ti:Sapphire femtosecond laser,solid-state nanosecond laser,C. elegans
更新于2025-09-23 15:19:57
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An Improved Room-Temperature Silicon Terahertz Photodetector on Sapphire Substrates
摘要： We design and fabricate a good performance silicon photoconductive terahertz detector on sapphire substrates at room temperature. The best voltage responsivity of the detector is 6679 V/W at frequency 300 GHz as well as low voltage noise of 3.8 nV/Hz1/2 for noise equivalent power 0.57 pW/Hz1/2. The measured response time of the device is about 9 ??s, demonstrating that the detector has a speed of >110 kHz. The achieved good performance, together with large detector size (acceptance area is 3 ??m×160 ??m), simple structure, easy manufacturing method, compatibility with mature silicon technology, and suitability for large-scale fabrication of imaging arrays provide a promising approach to the development of sensitive terahertz room-temperature detectors.
关键词： terahertz,room-temperature,sapphire substrates,silicon,photodetector
更新于2025-09-23 15:19:57