595-nm Pulsed Laser Research Articles

Dielectric laser acceleration of 28 keV electrons with the inverse Smith–Purcell effect

Dielectric laser acceleration exploiting the large optical field strength of short laser pulses and the proximity of a dielectric structure can support high acceleration gradients may therefore lead to much smaller accelerators, with future potential application in table-top free electron lasers. We report a proof-of-concept experiment demonstrating dielectric laser acceleration of non-relativistic 28keV electrons derived from a conventional scanning electron microscope column at a single fused-silica grating. The electrons pass the grating as closely as 50nm and interact with the third spatial harmonic, which is excited by 110fs long 800nm laser pulses with a peak electric field of 2.85GV/m. The observed maximum acceleration gradient of 25MeV/m is already comparable to state-of-the-art radio-frequency structures. This work thus represents a demonstration of scalable laser acceleration and of the inverse Smith–Purcell effect in the optical regime. For relativistic electrons and otherwise identical conditions up to two orders of magnitude larger acceleration gradients are expected.

Effectiveness and harmful effects of removal sulphated black crust from granite using Nd:YAG nanosecond pulsed laser

Sulphated black crust is a common form of deterioration affecting stone used in monuments, usually occurs in contaminated atmospheres or urban environments. Its origin and cleaning have been studied extensively, for decades, in the case of carbonate rocks. Recent studies show that this form of alteration also affects granites. Scientific research on laser removal effectiveness of gypsum-rich black crust on granites needs to be scientifically addressed considering the inexistent references.This paper assesses the removal by laser of sulphate-rich black crusts on granite using the different harmonics of a Nd:YAG nanosecond pulsed laser (266nm, 355nm, 532nm and 1064nm). Effectiveness was evaluated using Scanning Electron Microscopy with Energy Dispersive X-ray Spectrometry (SEM–EDS), X-Ray Diffraction (XRD) and Attenuated Total Reflection-Fourier Infrared Transform Spectroscopy (ATR-FTIR). We also evaluated the effect of the radiation on granite-forming minerals and on the colour of the stone using Scanning Electron Microscopy and spectrophotometry colour measurements respectively.SEM–EDS, XRD and ATR-FTIR analyses show that the higher the wavelength, the more efficient the cleaning, so samples cleaned using 1064nm pulsed laser recovered its original colour. Nevertheless, the Nd:YAG laser did not completely eliminate the crust, and gypsum crystals remaining on the rock surface are observed, even at the most effective wavelength.

Smooth silk fibroin nanofilm deposited by 1064-nm pulsed laser beam from an opaque target

In an attempt to prepare smooth nanostructured thin films of silk fibroin (SF) by near-infrared (NIR) pulsed laser deposition, an opaque target was prepared from an emulsified aqueous solution of SF. Upon irradiation of 1064-nm pulsed laser beam at its fluence 5J/cm2, a thin film of SF was deposited on the Si(100) substrate with its root-mean-square surface roughness, 0.37nm, smoother than those obtained from a compressed target of SF powders by approximately an order of magnitude. The attainment of an extra-smooth film from the opaque target was discussed in terms of multiple Mie scattering of the incident NIR beam, leading to an increase in the plasma density, intensified optical breakdown, ablation of better dispersed SF molecular units, and a film with more intensive intermolecular cross-linking.

Photo-ionization and photo-excitation of curcumin investigated by laser flash photolysis

Curcumin (Cur) has putative antitumor properties. In the current study, we examined photophysical and photochemical properties of Cur using laser flash photolysis. The results demonstrated that Cur could be photo-ionized at 355nm laser pulse to produce radical cation (Cur+) and solvated electron esol- in 7:3 ethanol–water mixtures. The quantum yield of Cur photo-ionization and the ratio of photo-ionization to photo-excitation were also determined. Cur+ could be transferred into neutral radical of Cur (Cur) via deprotonation with the pKa 4.13. The excited singlet of Cur (1Cur*) could be transferred into excited triplet (3Cur*), which could be quenched by oxygen to produce singlet oxygen 1O2∗. Reaction of 3Cur* with tryptophan was confirmed. The results encourage developing curcumin as a photosensitive antitumor agent.

Macro-atom versus many-electron effects in ultrafast ionization of C60

Ionization mechanisms of C${}_{60}$ molecules irradiated by a short intense 800-nm laser pulse are studied. Angle-resolved photoelectron spectra show above-threshold ionization (ATI) patterns with a low peak contrast and a remarkably smooth angular distribution. The results are interpreted by combining two theoretical models. A time-dependent Schr\odinger equation (TDSE) calculation based on the $B$-spline method that explicitly takes into account the molecular potential mimics the single-active-electron response while a statistical model accounts for the many-electron effects. We show that the latter are responsible for the loss of contrast in the ATI peaks. The smooth angular distribution arises in the TDSE calculation as a result of the high angular momentum of the C${}_{60}$ ground electronic state and therefore is a manifestation of the atomic behavior of the molecule.

Microfabrication of MOS H2 sensors based on Pd-gate deposited by pulsed laser ablation

A Nd:YAG high power 532nm pulsed laser was employed to deposit, a thin layer (30nm) of palladium on the gate of a microfabricated gas sensor (MOS capacitor). The functional performances of the MOS device were investigated by characterizing the capacitance (C–t, C–V) variations occurring upon H2 exposure, as a function of the gas concentration. A comparison in terms of sensor response versus concentration and recovery time was also performed with sensors in which the Pd layer was deposited by metal evaporation, maintaining all the parameters of the microfabrication process constant and by changing the operative working temperature. An improved performance was observed for the laser deposited Pd layer with respect to the evaporated one, an effect ascribed to the presence of Pd atoms into the underlying silicon oxide layer.

Side-by-side comparison of photodynamic therapy and pulsed-dye laser treatment of port-wine stain birthmarks

Pulsed-dye laser (PDL)-mediated photothermolysis is the current standard treatment for port-wine stain (PWS) birthmarks. Vascular-targeted photodynamic therapy (PDT) might be an alternative for the treatment of PWS. To compare clinical outcomes of PDT and PDL treatment of PWS. Two adjacent flat areas of PWS lesions were selected from each of 15 patients (two male and 13 female; age 11-36 years) and randomly assigned to either single-session PDL or PDT. PDL was delivered using a 585-nm pulsed laser. PDT was carried out with a combination of haematoporphyrin monomethyl ether (HMME) and a low-power copper vapour laser (510.6 and 578.2 nm). Clinical outcomes were evaluated colorimetrically and visually during follow-up. A total of nine red PWS lesions and six purple PWS lesions were treated. For red PWS, colorimetric assessment showed that the blanching rates of PDL and PDT at 2 months ranged from -11% to 24% and 22% to 55%, respectively. For purple PWS, blanching rates of PDL and PDT ranged from 8% to 33% and 30% to 45%, respectively. Overall, there was a significant difference between the blanching effect of single-session PDL treatment and a single-session PDT treatment. This side-by-side comparison demonstrates that PDT is at least as effective as PDL and, in some cases, superior. The true value of PDT for the treatment of PWS deserves further investigation.

Upconversion properties of Y2O3:Er,Yb nanoparticles prepared by laser ablation in water

Y2O3:Er,Yb nanoparticles were successfully prepared by laser ablation in liquid, and their upconversion properties were investigated. The particles were prepared by irradiating a Y2O3:Er,Yb target in water with a 532-nm pulsed laser beam. The prepared nanoparticles were determined to be composed of Y2O3, without any by-products, by X-ray diffraction. The average particle size of the nanoparticles measured by electron microscopy was a few tens of nanometers, which depended on the energy density of the irradiating laser beam. Upconversion luminescence of the nanoparticles was observed by the excitation of the laser diode at a wavelength of 980nm. An increase by 33% in the ratio of red emission (4F9/2→4I15/2) to green emission (2H11/2/4S3/2→4I15/2) was observed with a decrease in the size of the nanoparticles from 21.5nm to 11.1nm. This high ratio is useful for biomedical applications because of the high transparency of this wavelength in the human body. The number of photons generated by the upconversion luminescence of the nanoparticles was investigated. The number of photons involved in the process of the nanoparticles was three, which was attributed to nonradiative relaxation due to the large specific surface area of the particles; in contrast, the normal number of photons involved in the process of Y2O3:Er,Yb bulk is two.

Femtosecond laser damage of broadband pulse compression gratings

The fabricated gratings used for an 800-nm compressed laser pulse have more than 90% diffraction efficiency in the -1st order for TE polarization within 760-860 nm, and the maximum value is 94.3%. The laserinduced damage threshold (LIDT) of the gratings increases from 0.53 to 0.75 J/cm2 in the normal beam in a pulse width \tau of 40-100 fs. The LIDT of the gratings is observed a \tau^{0.25} scaling in the pulse width region. The damage morphologies of the gratings indicate that the initial damage of the gratings locates at the grating lines, a position that coincides with that of the electric field maximum.

Broadband water window supercontinuum generation with a tailored midinfrared laser pulse in asymmetric molecular gases

Theoretically, we investigate the high-order harmonic generation (HHG) from asymmetric molecules with a phase-stabilized few-cycle midinfrared laser pulse tailored by a much weaker 800-nm laser pulse. The results indicates that the ionization is almost restricted within half an optical cycle of the driving laser pulse and the energy difference between the photons emitted by the ejected electrons in this half optical cycle and its next half optical cycle is significantly enlarged. Then a 270eV water window supercontinuum is produced in the plateau of the high-order harmonic spectrum, from which an isolated water window 67 attoseconds pulse can be filtered directly. Moreover, this scheme can also be extended to the multi-cycle regime, enabling the generation of a broadband supercontinuum with higher photon energy and an intensity comparable to that of the lower-order harmonics.

Filament-induced breakdown remote spectroscopy in a polar environment

We demonstrate the feasibility of filament-induced breakdown spectroscopy (FIBS) for remote sensing of solid samples in a polar environment. FIBS spectra from an aluminum target induced by 800-nm laser pulses propagating in air were probed. The air visibility in an open winter field was as low as 3.2 km fluctuating with precipitation, pressure and relative humidity. Under such polar condition, clean spectral Al I lines from an aluminum target located at a distance of 60 m were obtained. This shows the technique FIBS could be potentially useful for sensing remote targets in a variety of polar environments.

Thermal annealing of laser damage precursors on fused silica surfaces

Previous studies have identified two significant precursors of laser damage on fused silica surfaces at fluences <35 J/cm2: photoactive impurities from polishing and surface fractures. We evaluate isothermal heating as a means of remediating the defect structure associated with surface fractures. Vickers indentations are applied to silica surfaces at loads between 0.5 and 10 N, creating fracture networks. The indentations are characterized before and following thermal annealing under various time and temperature conditions using confocal time-resolved photo-luminescence (CTP) imaging, and R/1 damage testing with 3-ns, 355-nm laser pulses. Improvements in the damage thresholds with reductions in CTP intensity are observed at temperatures well below the glass transition temperature (Tg). The damage threshold on 0.5-N indentations improves from <8 to >35 J/cm2 after annealing at approximately 750°C. Larger fracture networks require longer or higher temperature treatment to achieve similar results. At an annealing temperature >1100°C, optical microscopy indicates morphological changes in some of the fractures surrounding the indentations, although remnants of the original fractures are still observed. We demonstrate the potential of using isothermal annealing to improve the laser damage resistance of silica optics, and provide a means of further understanding the physics of optical damage and mitigation.

Effect of the 532nm pulsed KTP laser in the treatment of Reinke's edema

To evaluate the effect and safety of the 532nm Pulsed Potassium-Titanyl-Phosphate (KTP) laser in the office-based treatment of patients with Reinke's edema using objective and subjective scaled outcome measures. Case Series. Tertiary hospital center. Seven adult females undergoing in-office KTP laser treatment for Reinke's edema. Participants were studied pre- and posttreatment. Vocal function was evaluated by objective aerodynamic and acoustic analysis. Subjective changes were evaluated using the GRBAS scale, Voice Handicap Index, and videostroboscopy. Histologic effects of the laser were investigated by comparing one patient treated with laser one year prior to excision, one treated with laser just prior to excision, and one control patient who underwent excision without prior laser treatment. At an average postoperative follow up of 17.8 weeks (range 5-78), maximum phonation time trended toward improvement. The median VHI score decreased from 37 to 26 (p=0.150). There was a reduction in each component of the GRBAS scoring and the median fundamental frequency increased from 162 to 186 (p=0.625). Stroboscopic findings demonstrated an intact posttreatment mucosal wave. Histologic comparison of the tissue effects of laser in three patients demonstrated changes in vocal fold vascularity but no acute or long-term damage to the overlying epithelium. Objective and subjective scaled measures suggest that treatment of Reinke's edema in the office with a 532nm KTP laser may result in improved voice. It appears safe with histologic preservation of the vocal fold vibratory epithelium and persistence of mucosal wave.

The effect of laser wavelength on the formation of surface-microstructured silicon

We experimentally investigated the properties of the surface-microstructured silicon fabricated by 800 and 400nm laser pulses. We found that as the increasing of pulse number, the average height of spikes fabricated by the 800nm laser pulses increases more than that of the 400nm laser pulses. This is due to that the formation of the conic spike structure is originated from the conical distribution of incident laser energy in the sample, and the height of cone is proportional to the penetration depth of the laser pulse. Additionally, by comparing the samples which have similar average height of spikes, we found that the denser interval of spikes fabricated by the 400nm wavelength laser pulses has higher absorption coefficient than that of 800nm laser pulses. These results are beneficial for the preparation of high absorption surface-microstructured silicon.

Surface plasmon assisted electron acceleration in photoemission from gold nanopillars

Electron photoemission from lithographically prepared gold nanopillars using few-cycle, 800nm laser pulses is measured. Electron kinetic energies are observed that are higher by up to tens of eV compared to photoemission from a flat gold surface at the same laser intensities. In addition, ionization from the nanopillar sample scales like a two-photon process, while three photons are needed to overcome the work function taking into account the shortest wavelength within the laser bandwidth. A classical electron acceleration model consisting of nonlinear ionization followed by field acceleration qualitatively reproduces the electron kinetic energy data and suggests average enhanced electric fields due to the nanopillars that are between 25 and 39 times greater than the experimentally used laser fields. Implications for plasmon-enhanced attosecond streaking are discussed.

A dual-modality system for imaging anatomy and vasculature in live mouse embryos

An imaging system that combined high-frequency ultrasound (HFU) with photoacoustics (PA) for in vivo visualization of anatomical and vascular maps in transgenic mouse embryos is presented. The system consisted of a five-element, 40-MHz, poly-vinylidenefluoride-co-trifluoroethylene (PVDF-TrFE) annular array with a hole in the center to facilitate coaxial delivery of light produced by a 532-nm pulsed laser. A phosphate buffer-filled petri-dish with a central hole was placed on the abdomen of an anesthetized mouse and a laparotomy was performed to expose an intact uterus. The probe was raster scanned to achieve 3-D imaging. The central element of the array was excited with a high-voltage impulse synchronized with the light pulse. The resulting ultrasound echo and PA signal from each scan location were digitized from all five array channels and synthetically focused in post-processing. The embryonic vasculature depicted by the PA image was co-registered with anatomical features represented in the HFU image. T...

Third-order nonlinear optical response in transparent solids using ultrashort laser pulses

The third-order optical nonlinearity, χ (3), is measured in transparent glasses (BK7 and fused silica) and crystals (BaF2 and quartz) using 36-fs, 800-nm laser pulses and the optical Kerr gate (OKE) technique; values are found to lie in the range 1.3–1.7×10-14 esu, in accordance with theoretical estimates. We probe the purely electronic response to the incident ultrashort laser pulse in fused silica and BK7 glass. In BaF2 and quartz, apart from the electronic response we also observe contribution from the nuclear response to the incident ultrashort pulses. We observe oscillatory modulations that persist for ∼400 fs. The response of the media (glasses and crystals) to ultrashort pulses is also measured using two-beam self-diffraction; the diffraction efficiency in the first-order grating is measured to be in the range of 0.06–0.13 %. Third harmonic generation due to self-phase matching in the transient grating geometry is measured as a function of temporal delay between the two incident ultrashort pulses, yielding the autocorrelation signal.

Water molecules in ultrashort intense laser fields

Ionization and excitation of water molecules in intense laser pulses are studied theoretically by solving the three-dimensional time-dependent electronic Schrödinger equation within the single-active-electron approximation. The possibility to image orbital densities by measurement of the orientation-dependent ionization of H2O in few-cycle, 800nm linear-polarized laser pulses is investigated. While the highest-occupied molecular orbital 1b1 is found to dominate the overall ionization behavior, contributions from the energetically lower lying 3a1 orbital dominate the ionization yield in the nodal plane of the 1b1 orbital. The ratio of the ionization yields of the two orbitals depends on the intensity. Furthermore, even for laser pulses as long as 8 cycles the orientation-dependent ion yield depends on the carrier-envelope phase. In the interpretation of the orientation-dependent ionization as an imaging tool these effects have to be considered.

Local Injection of Bevacizumab (Avastin) and Angiolytic KTP Laser Treatment of Recurrent Respiratory Papillomatosis of the Vocal Folds: A Prospective Study

Photoangiolytic laser treatment of recurrent respiratory papillomatosis (RRP) is effective, but does not reliably prevent recurrence. Therefore, sublesional injections of the antiangiogenic agent bevacizumab (Avastin) were given to assess the adjunctive effect on disease recurrence. Since bevacizumab is a new therapeutic modality for RRP, there were also primary safety objectives to determine whether there was a pegative impact on the voice and whether there were local or systemic complications. A prospective open-label investigation was conducted in 20 adult patients with bilateral vocal fold RRP. The patients underwent planned 532-nm pulsed KTP laser photoangiolysis of bilateral glottal disease 4 times with an approximately 6-week interval between procedures. At each planned laser procedure, the vocal fold that on initial presentation had a greater volume of disease also underwent 4 serial sublesional bevacizumab injections (7.5 to 12.5 mg in 0.3 to 0.5 mL). A sham injection with saline solution was administered to the other vocal fold as a control. Disease resolution was compared between subjects' vocal folds, and objective measures of vocal function (acoustic, aerodynamic), as well as patients' self-assessments of vocal function (Voice-Related Quality of Life survey), were obtained. All 20 patients completed the study, and there were no local or systemic complications. After 4 injections, 3 of the 20 patients had no discernible disease in either vocal fold. Of the remaining 17 subjects, 16 had less disease in the bevacizumab-treated vocal fold despite starting with more disease. Only 1 of the 17 had more disease in the bevacizumab-treated vocal fold after 4 injections. Moreover, 7 of the 20 patients (35%) did not require a laser procedure in the vocal fold that had received 4 bevacizumab injections, as compared with 3 of the 20 vocal folds (15%) that were treated with laser alone. All of the vocal function measures displayed statistically significant posttreatment improvements, except for average fundamental frequency in the 3 female patients, in whom it fell below the normal range. This prospective investigation provided evidence that bevacizumab injections enhanced KTP laser treatment of glottal papillomatosis without systemic or local complications. Coupling the antiangiogenesis agent bevacizumab with KTP laser photoangiolysis is conceptually synergistic and scientifically promising since the mechanisms of action are complementary.

Office-based laser treatment of oral premalignant lesions

White and red lesions of the oral cavity remain a diagnostic and treatment challenge. Leukoplakia and erythroplakia are the most common premalignant lesions of the oral cavity (oral premalignant lesions [OPLs]). They have a potential for mucosal growth and malignant transformation. Obtaining a representative biopsy of the lesion is imperative to confirm histologic diagnosis and exclude malignant invasion. Subsequent management of such lesions includes observation, excision, ablation, or topical medical therapies. Despite these treatments, the lesions have a tendency to recur and prolonged observation with multiple retreatments is the rule rather than the exception. Laser treatment is well described for management of premalignant lesions. With the advent of smaller and more cost-effective lasers, this technology is now feasible for outpatient management of such lesions in the office setting. Furthermore, angiolytic lasers can be used to target the vasculature of oral lesions, leaving intact mucosa, which should result in less discomfort for the patient. We describe our management approach to premalignant oral cavity lesions as well as more benign oral cavity lesions amenable to treatment via an office-based laser. We also detail our experience and the theory behind various types of ablative and angiolytic lasers including CO 2 , thulium, 532-nm and 940-nm diode, and 532-nm pulsed potassium-titanyl phosphate laser in this setting.