Ps Pulses Research Articles

Variable magnetic field electron spectrometer to measure hot electrons in the range of 50-460 keV.

Resonance absorption (RA) occurs when a p-polarized electromagnetic wave, obliquely incident on an inhomogeneous plasma, tunnels past its turning point and resonantly excites an electron plasma wave (EPW) at the critical density. This phenomenon is important, for instance, in the direct drive approach to inertial fusion energy and is a particular example of a wider phenomenon in plasma physics known as mode conversion, which is crucial for heating magnetic fusion devices, such as tokamaks, via RF heating. Direct measurement of these RA-generated EPW accelerated hot electrons, with energy in the range of a few tens to a few hundreds of keV, is a challenging task due to the relatively low deflecting magnetic fields needed. The solution described here is a magnetic electron spectrometer (MES) with a continually changing magnetic field, lower at the entrance of the MES and gradually increasing toward the end, that enables the measurement of a wide spectral range of electrons with energies between 50 and 460keV. Electron spectra taken in a LaserNetUS RA experiment were acquired from plasmas generated by irradiating polymer targets with the combination of an ∼300ps pulse followed by a series of ten high intensity 50-200fs duration laser pulses from the ALEPH laser at Colorado State University. The high intensity beam is designed as spike trains of uneven duration and delay pulses in order to modify the RA phenomenon.

Ultrafast Laser Microlaryngeal Surgery for In Vivo Subepithelial Void Creation in Canine Vocal Folds.

Tightly-focused ultrafast laser pulses (pulse widths of 100 fs-10 ps) provide high peak intensities to produce a spatially confined tissue ablation effect. The creation of sub-epithelial voids within scarred vocal folds (VFs) via ultrafast laser ablation may help to localize injectable biomaterials to treat VF scarring. Here, we demonstrate the feasibility of this technique in an animal model using a custom-designed endolaryngeal laser surgery probe. Unilateral VF mucosal injuries were created in two canines. Four months later, ultrashort laser pulses (5 ps pulses at 500 kHz) were delivered via the custom laser probe to create sub-epithelial voids of ~3 × 3-mm2 in both healthy and scarred VFs. PEG-rhodamine was injected into these voids. Ex vivo optical imaging and histology were used to assess void morphology and biomaterial localization. Large sub-epithelial voids were observed in both healthy and scarred VFs immediately following in vivo laser treatment. Two-photon imaging and histology confirmed ~3-mm wide subsurface voids in healthy and scarred VFs of canine #2. Biomaterial localization within a void created in the scarred VF of canine #2 was confirmed with fluorescence imaging but was not visualized during follow-up two-photon imaging. As an alternative, the biomaterial was injected into the excised VF and could be observed to localize within the void. We demonstrated sub-epithelial void formation and the ability to inject biomaterials into voids in a chronic VF scarring model. This proof-of-concept study provides preliminary evidence towards the clinical feasibility of such an approach to treating VF scarring using injectable biomaterials. N/A Laryngoscope, 133:3042-3048, 2023.

Highly Regular LIPSS on Thin Molybdenum Films: Optimization and Generic Criteria.

A systematic experimental study was performed to determine laser irradiation conditions for the large-area fabrication of highly regular laser-induced periodic surface structures (HR-LIPSS) on a 220 nm thick Mo film deposited on fused silica. The LIPSS were fabricated by scanning a linearly polarized, spatially Gaussian laser beam at 1030 nm wavelength and 1.4 ps pulse duration over the sample surface at 1 kHz repetition rate. Scanning electron microscope images of the produced structures were analyzed using the criterion of the dispersion of the LIPSS orientation angle (DLOA). Favorable conditions, in terms of laser fluence and beam scanning overlaps, were identified for achieving DLOA values <10∘. To gain insight into the material behavior under these irradiation conditions, a theoretical analysis of the film heating was performed, and surface plasmon polariton excitation is discussed. A possible effect of the film dewetting from the dielectric substrate is deliberated.

Pulse Duration Effects on Solution-Phase Protein Desorption in Laser Electrospray Mass Spectrometry

The effect of laser pulse duration on the ablation of aqueous myoglobin is investigated using laser electrospray mass spectrometry (LEMS). Pulse durations of 55 femtoseconds (fs), 56 piscoseconds (ps), and 10 nanoseconds (ns) were used to ablate aqueous myoglobin from stainless-steel and quartz substrates. The integrated signal intensity of myoglobin increases with decreasing pulse duration for both substrates. Laser-induced thermal effects are assessed by the relative amount of solvent adduction and number of phosphate moieties adducted to myoglobin by each laser pulse duration. The mass spectra for 55 fs vaporization shows myoglobin with appreciable solvent and phosphate adduction and baseline elevation. The mass spectra for 10 ns ablation have minimal adduction and limited baseline elevation. Heat-induced conformation changes in myoglobin were used to measure the amount of thermal energy deposited by each laser pulse duration. Ablation using the 55 fs pulse revealed the highest ratio of unfolded to folded myoglobin in comparison to the 56 ps and 10 ns measurements due to increased droplet lifetime and consequent interaction with the acid in the electrospray solvent. Collisional activation and heated capillary temperature were employed to reduce the droplet lifetime and demonstrate that fs ablation preserves approximately 2 times more myoglobin folded conformation in comparison to ps and ns pulses.

Synthesis and nonlinear optical properties of polyurethane composites containing a pyrene derivative.

The pyrene derivative (PD) was synthesized with pyrene-1-carboxaldehyde and p-aminoazobenzene by a Schiff base reaction. Then the obtained PD was dispersed in polyurethane (PU) prepolymer to prepare polyurethane/pyrene derivative PU/PD materials with good transmittance. The nonlinear optical (NLO) performances of the PD and PU/PD materials were studied by the Z-scan technique under picosecond and femtosecond laser pulses. The PD has reverse saturable absorption (RSA) properties under the excitation of 532nm 15ps pulses, 650 and 800nm 180fs pulses, and a low optical limiting (OL) threshold (0.01J/c m 2). The PU/PD has a larger RSA coefficient than that of the PD under 532nm 15ps pulses. With the enhanced RSA, the PU/PD materials exhibit excellent OL (OL) performance. Good NLO properties, high transparency, and easy processing performances make the PU/PD an excellent choice for use in OL and laser protection fields.

Laser Ablation Study of Cutting Ceramics with Consideration of the Beam Inclination Angle

Silicon alumina nitride (SiAlON) and alumina toughened zirconia (ATZ) ceramics are applied for ceramic cutting tools to machine, e.g., cast iron, nickel base alloys and other difficult-to-machine materials. The state of the art technology for manufacturing of the cutting tool geometry is grinding. Laser processing of ceramics is already studied in terms of ablation rate and roughness evaluation with the application of dental implant manufacturing. In the present study, laser machining of the mentioned ceramics is explored with a laser beam source of 1064 nm wavelength and 10 ps pulse duration (FWHM). The angle dependent energy specific removal rate is described in a model and the optimal pulse fluence for the different materials and the irradiation angles can be derived. For processing at irradiation angle of up to 75° no decrease of the relative absorption could be observed. For ATZ, lowest surface roughness is determined for both, orthogonal and quasi-tangential processing angle. For SiAlON, the roughness decreases constantly for higher tilt angles. A significant difference in the material answer with change of the sample composition can be detected and the results show the potential of further developing SiAlON ceramics towards machineability for laser ablation.

Spectral properties of IR-filamentation in air induced by 1 ps pulses for coherent anti-Stokes Raman scattering

We investigate the spectral properties of ps laser-induced filamentation in air using an ultrafast thin-disk based amplifier at a central wavelength of 1030 nm with a maximum pulse energy of 60 mJ at a repetition rate of 1 kHz. We show that the spectrum induced by filamentation in air is sufficiently broad to excite ro-vibrational Raman transitions in N2, O2 and CH4. The excitation is probed with the second harmonic (515 nm) to generate CARS signals in air. Furthermore, we investigate the influence of optical windows on the CARS signal for applications in combustion and gasification diagnostics.

All-Polarization-Maintaining, Mode-Locked 488 nm Picosecond Laser

In this letter, we report a 488 nm blue picosecond pulse generation by frequency doubling of a homemade 977 nm watt-level picosecond all polarization maintaining mode-locked fiber laser. Based on a SESAM passively mode-locked Yb-doped fiber linear cavity configuration, the 977 nm picosecond seed laser shows a 977.84 nm central wavelength, 0.13 nm spectral width, 12.94 ps pulse duration, 76.09 MHz repetition rate, and 5.12 mW average power, respectively. The average power is further scaled up to 2.06 W by adopting an all-fiber MOPA structure, and the pulse duration and spectral width are slightly broadened to 16.84 ps and 0.24 nm, respectively. Furthermore, a 147.40 mW blue picosecond pulsed laser with a 488.92 nm central wavelength and 0.17 nm linewidth is successfully achieved by frequency doubling in a MgO2:PPLN crystal. Such compact, high-power, and narrow-linewidth picosecond blue laser is a promising candidate for high-resolution imaging, underwater detection and material processing, etc.

Watt-level deep-UV subnanosecond laser system based on Nd-doped fiber at 229 nm.

We report an efficient deep-UV master-oscillator power amplifier (MOPA) laser system at 229 nm that generates 350 ps pulses at 2 MHz repetition rate with an average power of 1.2 W. The use of a polarization-maintaining large mode area neodymium-doped fiber operating on the 4F3/2→4I9/2 transition allows high-power laser emission of up to 28 W near 915 nm in the sub-nanosecond regime with low spectral broadening. Two nonlinear frequency conversion stages (LBO + BBO crystals) in a single-pass configuration directly convert the IR laser emission to deep UV. This laser demonstrates the great potential of Nd3+-doped fiber lasers to produce high-power deep-UV emission.

Raman Generation of PS Pulses at λ= 3.9 μm in a Hollow-Core Revolver Fiber

Raman Generation of PS Pulses at λ= 3.9 μm in a Hollow-Core Revolver Fiber

The Nonlinear Optical Properties of Ferrocene-containing Metalloporphyrins Toward the Pico-second Laser

Background: The nonlinear optical properties of ferrocene-containing metalloporphyrins toward pico-second laser were studied using calculational and experimental methods, and the relationship between their structures and nonlinear absorption properties were discussed. Aims: The metal ions introduced into the porphyrin rings intensively affect the nonlinear optical properties. Methods: The nonlinear optical properties and the relationship between the property and the structure of the synthesized ferrocene-containing metalloporphyrins are studied using the calculational method and the open-aperture Z-scan technology for pico-second laser. Results: The Z-scan results show that Co-P-Fc, Zn-P-Fc and Pd-P-Fc exhibit reverse saturable absorption characteristics toward the laser with 532 nm wavelength and 21 ps pulse width, and the nonlinear absorption coefficients (β) of them were 4.1, 3.2 and 1.3 cm/GW, respectively, when the incident laser fluency at the focal point of the lens is 29 mJ/cm2. In addition, the values of β decrease with the increase of the incident laser fluency. These results indicate that the nonlinear absorption characteristics of Co-P-Fc, Zn-P-Fc and Pd-P-Fc are ascribed to the excited state absorption (ESA). However, Cu-PFc, Ni-P-Fc and P-Fc show saturated absorption characteristics toward the ps laser pulse. Conclusion: To elucidate the intrinsic factors that influence the nonlinear optical properties, the electronic distribution, flow of charge density during the transition from the ground state to the excited state, and the first-order hyperpolarizability values (β) are calculated using the time-dependent density functional theory (TD-DFT). The calculated results show that the molecular polarity and the change of the molecular polarity before and after the transition from HOMO to LUMO, which is dominated by the redox potentials of the introduced metal ions, are the most important factors that affect the nonlinear optical properties of the title compounds.

Nb2AlC as saturable absorber for a passively mode-locked operation of Tm:YLF laser

The Nb2AlC material has attracted more and more attention in optoelectronics due to its excellent optical properties. Herein, the Nb2AlC-based saturated absorber (SA) was fabricated by ultrasonic thermal dissolution method and spin coating means, and a passively mode-locked (PML) Tm:YLF laser was perfectly demonstrated with the SA. With an incident pump power of 21.63W, a 0.379-W average output power and a 200-ps pulse width were achieved at 1872.1nm, corresponding to a per pulse energy of 3.15nJ and a peak power of 15.75W. In addition, the beam quality factors were measured to be 1.04 and 1.05 in the horizontal direction and vertical direction.

Ultrafast L Band Soliton Pulse Generation in Erbium-Doped Fiber Laser Based on Graphene Oxide Saturable Absorber

We demonstrate a simple mode-locked Erbium-doped fiber laser (EDFL) based on self-synthesized saturable absorber (SA) by combining graphene oxide (GO) and polyethylene oxide (PEO) solutions to form a GO-PEO thin film. This thin film was incorporated into an Erbium-doped fiber laser (EDFL) with a cavity length of 9 m. Our EDFL could operate at a 22 MHz repetition rate with a 0.8 ps pulse duration. The laser also showed stable soliton pulses under various laser pump power values. Our reported results show that GO-PEO SA is effective and proven as a cost-effective material for saturable absorbers for EDFLs.

Ultrafast laser heating for controlling the optoelectronic properties of sulfur hyperdoped black silicon

Ultrashort pulse laser processed sulfur hyperdoped black silicon represents a promising silicon-based material for infrared optoelectronic applications due to its high sub-bandgap optical absorptance. Non-thermal melting and resolidification processes associated with such laser processing, however, result in amorphous and polycrystalline phases which may be detrimental for this purpose. Furthermore, the sulfur impurities are electrically inactive, impeding the formation of a rectifying junction. This work demonstrates an ultrafast laser heating process based on heat accumulation with laser pulses of 10 ps pulse duration at high repetition rates of 41 MHz and peak fluences between 33% and 66% of the ablation threshold as a method to (i) recrystallize the material and (ii) electrically activate the sulfur dopants while (iii) maintaining the sub-bandgap absorption. Furthermore, laser heating recovers the optical activity of sulfur states that have been previously deactivated by thermal annealing. The demonstrated process can have versatile applications in material functionalization due to its highly localized heat input accompanied by high cooling rates.

High-energy, hundred-picosecond pulsed 266 nm mid-ultraviolet generation by a barium borate crystal

Abstract We present a high-energy, hundred-picosecond (ps) pulsed mid-ultraviolet solid-state laser at 266 nm by a direct second harmonic generation (SHG) in a barium borate (BaB2O4, BBO) nonlinear crystal. The green pump source is a 710 mJ, 330 ps pulsed laser at a wavelength of 532 nm with a repetition rate of 1 Hz. Under a green pump energy of 710 mJ, a maximum output energy of 253.3 mJ at 266 nm is achieved with 250 ps pulse duration resulting in a peak power of more than 1 GW, corresponding to an SHG conversion efficiency of 35.7% from 532 to 266 nm. The experimental data were well consistent with the theoretical prediction. To the best of our knowledge, this laser exhibits both the highest output energy and highest peak power ever achieved in a hundred-ps/ps regime at 266 nm for BBO-SHG.

High-efficiency bismuth borate-based optical parametric chirped pulse amplifier with approximately 2.1 mJ, 38 fs output pulses at approximately 2150 nm

Abstract We present a compact and cost-effective mJ-level femtosecond laser system operating at a center wavelength of approximately 2.15 μm. An affordable two-stage ytterbium-doped yttrium aluminum garnet (Yb:YAG) chirped pulse amplifier provides more than 10 mJ, approximately 1.2 ps pulses at 1030 nm to pump a three-stage optical parametric chirped pulse amplifier (OPCPA) based on bismuth borate crystals and to drive the supercontinuum seed in the YAG crystal. The energy of the amplified pulses in the wavelength range of 1.95–2.4 μm reached 2.25 mJ with a pump-to-signal conversion efficiency of approximately 25% in the last OPCPA stage. These pulses were compressed to 38 fs in a pair of Suprasil 300 glass prisms.

Nonlinear ionization control by temporally shaped fs+ps double-pulse sequence on ZnO

We designed a femtosecond (fs) + picosecond (ps) double-pulse sequence by using a Mach–Zehnder-like apparatus to split a single 120 fs pulse into two sub-pulses, and one of them was stretched to a width of 2 ps by a four-pass grating system. Through observing the ripples induced on the ZnO surface, we found the ionization rate appeared to be higher for the sequence in which the fs pulse arrived first. The electron rate equation was used to calculate changes of electron density distribution for the sequences with different delay times. We suggest that using a temporally shaped fs+ps pulse sequence can achieve nonlinear ionization control and influence the induced ripples.

High-Sensitivity Thomson Spectrometry in Experiments of Laser-Driven Low-Rate NeutronLess Fusion Reactions

The aneutronic 11B(p, α)2α fusion reaction driven by the interaction of high-energy lasers with matter has become a popular topic of research, since it represents a potential long-term goal alternative to the most studied deuterium-tritium reaction. However, the detection of the typical ionic products, especially alpha particles, of this low-rate fusion reaction is a challenging issue, due to their low flux. One of the diagnostic devices that can be implemented in laser-driven proton-boron fusion experiments is a Thomson spectrometer (TS), which is capable of detecting and discriminating ions according to their mass-to-charge ratio (A/Z, where A is the mass number and Z is the atomic number of the ions). In this work, we report on the ultimate test of a TS, which was designed and developed at the ENEA Research Centre in Frascati, Italy, in the context of a p + 11B fusion experiment. Our device—designed to have high sensitivity and a robust shielding against electromagnetic pulses (EMPs)—was implemented at the PALS laser facility (∼700 J in ∼350 ps pulses) at a distance of 367 mm from the laser-plasma interaction point. We analyse here the measured signals obtained with our device, focusing on the assessment of their signal-to-background ratio. Despite the presence of strong EMPs and background radiation at such a short distance from the laser-irradiated target, the TS proved to be suitable for effectively detecting protons and heavier ions stemming from the plasma source.

Thermo-mechanical coupling induced Near-threshold double pulses femtosecond laser ablation enhancement in titanium

Near-threshold femtosecond laser surface treatment of titanium produces functional nanostructures, which has received much attention in applications and scientific researches. However, researches on the mechanism of near-threshold temporally-shaped femtosecond laser ablation of titanium are scarce, because the difficulty of investigating the modification mechanism of surface properties by sub-pulses below the ablation threshold. In this study, the double-pulse femtosecond laser ablation with various pulse separation was investigated. We found that the maximum ablation area appeared around 1 ps pulse separation at different fluences, and the ablation enhancement weakened with the increase of the fluence. The ultrafast pump–probe microscopy technique and ultrafast thermoelasticity model were used to investigate the mechanism. The result of pump–probe microscopy technique indicated that the enhancement of the area was caused by the decrease of transient reflectivity in the early stages which facilitated the subsequent sub-pulse energy absorption. The theoretical results indicate that the maximum ablation enhancement occurred at 1 ps, which is due to the combination of thermal and mechanical effects. The maximum of long axis diameter of periodic structure also appeared at 1 ps in multi-point processing. These findings have significant implications for the modulation of titanium surface nanostructures and providing theoretical support for processing.

CoS nanosheets for generation of vector soliton and bound solitons in nonlinear optical fiber system

Transition metal chalcogenides (TMCs) with two-dimensional (2D) structures are of great interest for their extraordinary electrical, optical, magnetic, and mechanical properties. In this work, a novel cobalt sulfide (CoS) nanosheets (NSs) based saturable absorber (SA) with a modulation depth of 6.4 % is fabricated through liquid phase exfoliation (LPE) method, and successfully applied to a passive mode-locked erbium-doped fiber laser (PML-EDFL) for the first time as far as we know. By adjusting the pump power and optimizing the orientation of the intra-cavity polarization controller, a stable conventional solitons (CS) pulse with a duration of 905 fs and signal-to-noise ratio (SNR) of 58.5 dB at fundamental repetition frequency of 4.03 MHz, a pair of bound solitons with time interval of 4.9 ps between two 1.8 ps pulses are generated in proposed PML-EDFL. Meanwhile, the vector characteristics of generated soliton pulse are investigated, and polarization-locked vector solitons are observed. The results reveal that the CoS NSs have superior polarization insensitive nonlinear optical modulation properties and will find extensive application potential in the ultrafast photonics.