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Materials (Basel, Switzerland) Dec 2018The fabrication of micro-holes in silicon substrates that have a proper taper, higher depth-to-diameter ratio, and better surface quality has been attracting intense...
The fabrication of micro-holes in silicon substrates that have a proper taper, higher depth-to-diameter ratio, and better surface quality has been attracting intense interest for a long time due to its importance in the semiconductor and MEMS (Micro-Electro-Mechanical System) industry. In this paper, an experimental investigation of the machining performance of the direct and chemical-assisted picosecond laser trepanning of single crystalline silicon is conducted, with a view to assess the two machining methods. The relevant parameters affecting the trepanning process are considered, employing the orthogonal experimental design scheme. It is found that the direct laser trepanning results are associated with evident thermal defects, while the chemical-assisted method is capable of machining micro-holes with negligible thermal damage. Range analysis is then carried out, and the effects of the processing parameters on the hole characteristics are amply discussed to obtain the recommended parameters. Finally, the material removal mechanisms that are involved in the two machining methods are adequately analyzed. For the chemical-assisted trepanning case, the enhanced material removal rate may be attributed to the serious mechanical effects caused by the liquid-confined plasma and cavitation bubbles, and the chemical etching effect provided by NaOH solution.
PubMed: 30583577
DOI: 10.3390/ma12010041 -
Optics Express Nov 2022A high-average-power, high-pulse-energy picosecond chirped pulse amplification (CPA) laser system based on an extra-large-mode-area (XLMA) triple-clad fiber (TCF) was...
A high-average-power, high-pulse-energy picosecond chirped pulse amplification (CPA) laser system based on an extra-large-mode-area (XLMA) triple-clad fiber (TCF) was demonstrated. The ultrashort pulses, generated from all-fiber mode-locked oscillator, stretched and then were pre-amplified to 10 W through a series of fiber power amplifiers. Subsequently, the average output power was amplified to 620 W corresponding to a pulse energy of 0.62 mJ via XLMA TCF. Additionally, the amplified pulses were compressed to a pulse duration of 7.6 ps with an average power of 423 W and a compression efficiency of 68.2%. The ultrashort laser is a promising light source for application of water-guided laser processing, albeit with a beam quality factor of 20 and 21 along two orthogonal axes.
PubMed: 36366601
DOI: 10.1364/OE.469197 -
Lasers in Medical Science Jul 2023Fractional picosecond-domain lasers (PSL) induce optical breakdown, which correlates histologically to vacuolization in the epidermis and dermis. In this ex vivo porcine...
Fractional picosecond-domain lasers (PSL) induce optical breakdown, which correlates histologically to vacuolization in the epidermis and dermis. In this ex vivo porcine study, we sought to establish a framework for the investigation of laser-tissue interactions and their dependence on melanin density. Light- (melanin index: 24.5 [0-100]), medium- (58.7), and dark-pigmented (> 98) porcine skin samples were exposed to a 755-nm fractional PSL and examined with dermoscopy, line-field confocal optical coherence tomography (LC-OCT), conventional OCT, and subsequently biopsied for digitally stained ex vivo confocal microscopy (EVCM) and histology, using hematoxylin and eosin (HE) and Warthin-Starry (WS) melanin staining. Dermoscopy showed focal whitening in medium- and dark-pigmented skin. Similarly, LC-OCT and OCT visualized melanin-dependent differences in PSL-induced tissue alterations. Vacuoles were located superficially in the epidermis in dark-pigmented skin but at or below the dermal-epidermal junction in medium-pigmented skin; in light-pigmented skin, no vacuoles were observed. Histology confirmed the presence of vacuoles surrounded by areas void of WS staining and disrupted stratum corneum in darker skin. The combined use of optical imaging for multiplanar visualization and histological techniques for examination of all skin layers may mitigate the effect of common artifacts and attain a nuanced understanding of melanin-dependent laser-tissue interactions.
Topics: Animals; Swine; Melanins; Skin; Lasers, Solid-State; Microscopy, Confocal; Tomography, Optical Coherence; Histological Techniques
PubMed: 37450199
DOI: 10.1007/s10103-023-03811-4 -
Skin Research and Technology : Official... Jan 2023To evaluate the efficacy and safety of fractional 1064 nm picosecond Nd:YAG laser (FPNYL) in the treatment of post-acne erythema (PAE) of adult Chinese.
OBJECTIVE
To evaluate the efficacy and safety of fractional 1064 nm picosecond Nd:YAG laser (FPNYL) in the treatment of post-acne erythema (PAE) of adult Chinese.
MATERIALS AND METHODS
A total of 22 patients received 1 session of treatment and were followed up at the eighth week. Primary outcomes were measured by the Clinician erythema assessment scale (CEAS). Secondary outcomes included a global aesthetic improvement scale (GAIS) and patients' assessment of satisfaction on a five-point scale. Pain scores and adverse effects were also evaluated.
RESULTS
Twenty-two patients with Fitzpatrick skin types III and IV were enrolled in the study and completed all treatments and follow-up visits. The mean CEAS scores fell from 2.74 ± 0.80 to 1.95 ± 0.75 (p < 0.05). The mean GAIS of PAE improvement was 2.46 ± 0.68. Erythema percentile scores by VISIA increased from 32.63 ± 7.0 to 45.75 ± 11.45 (t = 5.442, p = 0). The patient satisfaction score was 1.86 ± 1.17. The pain scores were 3.27 ± 1.17 for the FPNYL treatment (varied from 2 to 6). There were moderate erythema and oedema, which last for 3.84 ± 0.78 days. There were overall 68.18% (15/22) patients who felt pruritus in different degrees and 27.27% patients who encountered acne eruptions (white head type). No scar, hyperpigmentation or hypopigmentation was found.
CONCLUSION
Treatment with fractional 1064 nm picosecond Nd:YAG laser is effective and safe for PAE of Chinese patients.
Topics: Humans; Adult; Treatment Outcome; East Asian People; Acne Vulgaris; Erythema; Cicatrix; Lasers, Solid-State; Pain
PubMed: 36704883
DOI: 10.1111/srt.13274 -
Angewandte Chemie (International Ed. in... Jul 2022The chemical reactivity of nitrile imines is of great utility in organic synthesis with applications rapidly expanding into the materials and life sciences. Yet, our...
The chemical reactivity of nitrile imines is of great utility in organic synthesis with applications rapidly expanding into the materials and life sciences. Yet, our understanding of the electronic and molecular structures of nitrile imines remains incomplete and the elementary mechanism of their photoinduced generation is entirely unknown. Here, femtosecond infrared spectroscopy after 266 nm-excitation of 2,5-diphenyltetrazole has been carried out to temporally resolve the formation and structural relaxation dynamics of the nascent diphenylnitrile imine in liquid solution under ambient conditions. The infrared-spectroscopic evolution is interpreted by an initial sequence of intersystem crossings within 250 fs followed by the cleavage of N with formation of a structurally relaxed nitrile imine on the adiabatic ground-state singlet surface within a few tens of picoseconds. The infrared spectrum supports the notion of a "floppy" nitrile imine molecule whose equilibrium character ranges from fully propargylic to fully allenic in the room temperature liquid solution.
PubMed: 35583254
DOI: 10.1002/anie.202205803 -
Micromachines Nov 2022This paper introduces a novel nondestructive wafer scale thin film thickness measurement method by detecting the reflected picosecond ultrasonic wave transmitting...
This paper introduces a novel nondestructive wafer scale thin film thickness measurement method by detecting the reflected picosecond ultrasonic wave transmitting between different interfacial layers. Unlike other traditional approaches used for thickness inspection, this method is highly efficient in wafer scale, and even works for opaque material. As a demonstration, we took scandium doped aluminum nitride (AlScN) thin film and related piezoelectric stacking layers (e.g. Molybedenum/AlScN/Molybdenum) as the case study to explain the advantages of this approach. In our experiments, a laser with a wavelength of 515 nm was used to first measure the thickness of (1) a single Molybdenum (Mo) electrode layer in the range of 100-300 nm, and (2) a single AlScN piezoelectric layer in the range of 600-1000 nm. Then, (3) the combined stacking layers were measured. Finally, (4) the thickness of a standard piezoelectric composite structure (Mo/AlScN/Mo) was characterized based on the conclusions and derivation extracted from the aforementioned sets of experiments. This type of standard piezoelectric composite has been widely adopted in a variety of Micro-electromechanical systems (MEMS) devices such as the Piezoelectric Micromachined Ultrasonic Transducer (PMUT), the Film Bulk Acoustic Resonator (FBAR), the Surface Acoustic Wave (SAW) and more. A comparison between measurement data from both in-line and off-line (using Scanning Electron Microscope) methods was conducted. The result from such in situ 8-inch wafer scale measurements was in a good agreement with the SEM data.
PubMed: 36363937
DOI: 10.3390/mi13111916 -
Optics Express Apr 2021Free-space optical time and frequency transfer techniques can synchronize fixed ground stations at the femtosecond level, over distances of tens of kilometers. However,...
Free-space optical time and frequency transfer techniques can synchronize fixed ground stations at the femtosecond level, over distances of tens of kilometers. However, optical time transfer will be required to span intercontinental distances in order to truly unlock the performance of optical frequency standards and support an eventual redefinition of the SI second. Fiber dispersion and Sagnac uncertainty severely limit the performance of long-range optical time transfer over fiber networks, so satellite-based free-space time transfer is a promising solution. In pursuit of ground-to-space optical time transfer, previous work has considered a number of systematic shifts and concluded that all of them are manageable. One systematic effect that has not yet been substantially studied in the context of time transfer is the effect of excess optical path length due to atmospheric refraction. For space-borne objects, orbital motion causes atmospheric refraction to be imperfectly canceled even by two-way time and frequency transfer techniques, and so will require a temperature-, pressure-, and humidity-dependent correction. This systematic term may be as large as a few picoseconds at low elevations and remains significant at elevations up to ~35. It also introduces biases into previously-studied distance- and velocity-dependent corrections.
PubMed: 33985100
DOI: 10.1364/OE.421620 -
Photoacoustics Oct 2023Photoacoustic (PA) theranostics is a new emerging field that uniquely combines diagnosis and treatment in one modality. However, its current status is compromised by the...
Photoacoustic (PA) theranostics is a new emerging field that uniquely combines diagnosis and treatment in one modality. However, its current status is compromised by the indispensable dependence on nonreversible phase-change nanoprobes that provides one-time-only action. Here, we demonstrate a picosecond-laser-pumped ultrafast PA cavitation technique for highly efficient shockwave theranostics, guaranteeing sustained PA cavitation by using non-phase-change nanoprobes. Theoretical simulations validate that, when compressing the excitation laser pulse width to hundred-picosecond, the thermal confinement effects of a conventional nanoprobe will induce transient heating of the extremely thin surrounding liquid layer of the nanoprobes beyond its cavitation point in a localized area at nanoscale, resulting in intense cavitation and PA shockwaves by the environment rather than the nanoprobes. Both cellular and mouse model experiments have demonstrated the highly effective anti-tumor effects. This method provides a sustainable, reproducible, and highly effective strategy for PA theranostics, prefiguring great potential for the clinical applications.
PubMed: 38021291
DOI: 10.1016/j.pacs.2023.100546 -
The Journal of Physical Chemistry. C,... May 2024Methylammonium lead tribromide perovskite (MAPbBr) is an important material, for example, for light-emitting applications and tandem solar cells. The relevant...
Methylammonium lead tribromide perovskite (MAPbBr) is an important material, for example, for light-emitting applications and tandem solar cells. The relevant photophysical properties are governed by a plethora of phenomena resulting from the complex and relatively poorly understood interplay of excitons and free charge carriers in the excited state. In this study, we combine transient spectroscopies in the visible and terahertz range to investigate the presence and evolution of excitons and free charge carriers at ultrafast times upon excitation at various photon energies and densities. For above- and resonant band-gap excitation, we find that free charges and excitons coexist and that both are mainly promptly generated within our 50-100 fs experimental time resolution. However, the exciton-to-free charge ratio increases upon decreasing the phonon energy toward resonant band gap excitation. The free charge signatures dominate the transient absorption response for above-band-gap excitation and low excitation densities, masking the excitonic features. With resonant band gap excitation and low excitation densities, we find that although the exciton density increases, free charges remain. We show evidence that the excitons localize into shallow trap and/or Urbach tail states to form localized excitons (within tens of picoseconds) that subsequently get detrapped. Using high excitation densities, we demonstrate that many-body interactions become pronounced and effects such as the Moss-Burstein shift, band gap renormalization, excitonic repulsion, and the formation of Mahan excitons are evident. The coexistence of excitons and free charges that we demonstrate here for photoexcited MAPbBr at ultrafast time scales confirms the high potential of the material for both light-emitting diode and tandem solar cell applications.
PubMed: 38835933
DOI: 10.1021/acs.jpcc.3c08509 -
Scientific Reports Nov 2020Endoluminal surgery for the treatment of colorectal neoplasia is typically carried out using electrocautery tools which imply limited precision and the risk of harm...
Endoluminal surgery for the treatment of colorectal neoplasia is typically carried out using electrocautery tools which imply limited precision and the risk of harm through collateral thermal damage to the adjacent healthy tissue. As a potential alternative, we present the successful colonic epithelial laser ablation by means of picosecond laser pulses. Laser ablation studies performed in ex-vivo colon tissue result in cavities with comparable thickness to early stage colorectal cancers. The corresponding histology sections exhibit only minimal collateral damage to the surrounding tissue and the depth of the ablation can be controlled precisely by means of the pulse energy. High-speed imaging has been used for the first time to visualize picosecond laser ablation of cancerous tissue in a clinically relevant model. This information was correlated with histopathology and optical surface profilometry revealing the dynamic nature of the laser tissue interaction and the need for temporal or spatial separation of pulses for optimum efficacy with regards to tissue removal. Overall, the application of picosecond laser pulses to ablate endoluminal bowel lesions demonstrates significantly improved precision and reduced thermal damage to the adjacent tissue in comparison to conventional procedures and hence will enable more precise surgical treatment of cancers.
Topics: Animals; Colorectal Neoplasms; Disease Models, Animal; Laser Therapy; Mice; Swine
PubMed: 33219260
DOI: 10.1038/s41598-020-73349-w