Picosecond Laser System Research Articles

Choose your own adventure: Picosecond or broadband vibrational sum-frequency generation spectroscopy.

Vibrational sum-frequency generation (VSFG) spectroscopy is a method capable of measuring chemical structure and dynamics within the interfacial region between two bulk phases. At the core of every experimental system is a laser source that influences the experimental capabilities of the VSFG spectrometer. In this article, we discuss the differences between VSFG spectrometers built with picosecond and broadband laser sources as it will impact everything from material costs, experimental build time, experimental capabilities, and more. A focus is placed on the accessibility of the two different SFG systems to newcomers in the SFG field and provides a resource for laboratories considering incorporating VSFG spectroscopy into their research programs. This Tutorial provides a model decision tree to aid newcomers when determining whether the picosecond or femtosecond laser system is sufficient for their research program and navigates through it for a few specific scenarios.

8 mJ 355 nm 1 kHz burst-mode picosecond laser systems

This paper presents an 8 mJ 355 nm 1 kHz burst-mode picosecond laser system, where the energy of each subpulse in the burst mode is 2 mJ. Under optimal operational conditions, a noncritical phase-matched LiB3O5 (LBO) crystal and a type-II angle- and phase-matched LBO crystal are used as the second- and third-harmonic generation crystals, respectively. The largest conversion efficiency from 1064 nm to 355 nm was 38%, and the highest output power at 355 nm was 8 W; further, the beam quality was measured as and .

Towards Ultrafast Laser Micromachining of X-Ray Gratings and Creation of Sub-Micron Hole Patterns, Comparison of Results With Bessel and Gaussian Beams

We compare micromachining results with Gaussian and Bessel beams using an UV picosecond laser system and demonstrate feasibility to produce tungsten gratings for x-ray interferometry medical imaging, and sub-micrometer size hole patterns. The advantages of Bessel beams compared to Gaussian beams, are demonstrated for micromachining of rectangular shallow profile gratings with sharp edges. The high-aspect ratio grating (10 microns wide and 200 microns deep) from tungsten foil could only be obtained with the Gaussian beam and focusing with an F-Theta type lens. Bessel beams contain significant amount of energy in the side lobes in comparison with the central peak. The limited amount of the pulse energy in the central, 2-micron peak of the beam and destruction of the Bessel beam structure due to the narrow slit clipping the side lobes, prevented the Bessel beam deeper penetration. On the other hand, the axicon lens and the Bessel beam shape enable creation of shallow sub-micron size structures.

310 W picosecond laser based on Nd:YVO4 and Nd:YAG rod amplifiers

Herein, a high-power picosecond laser system based on master oscillator power amplifier structure is demonstrated. The seed source is a SESAM mode-locked fiber oscillator; the pulse repetition frequency is selected by an acoustic optical modulator with a tunable range from 100 kHz to 4.27 MHz. The amplification system includes one fiber amplifier stage, four stages of end-pumped Nd:YVO4 amplifiers, and two stages of side-pumped Nd:YAG amplifiers. Finally, the average output power of >300 W is achieved. The maximum peak power is 86.6 MW at 300 kHz with a pulse energy of ∼700 μJ and a pulse duration of ∼8.08 ps.

Ring droplet formation during evaporation of a sessile water droplet on a biphilic surface

Numerous studies have investigated droplet evaporation on surfaces with different roughness and wettability values. However, most studies have focused on droplet evaporation from homogeneous surfaces at low surface temperatures (below 100 °C). In this study, we conducted droplet evaporation experiments on biphilic surfaces with different ring pattern sizes fabricated by a hybrid method consisting of the sol-gel approach and a picosecond laser system. This study investigated the droplet evaporation boiling phenomenon on these biphilic surfaces under superheated conditions. Changes in droplet geometry and inner bubble dynamics during evaporation were analyzed using a high-speed camera. A ring-shaped droplet formed during the final evaporation period. The formation of the ring enhanced the droplet evaporation efficiency. Furthermore, the experimental results from this study work were compared with the theoretical model proposed in the literature.

Acceleration of electrons in hollow glass capillaries under the action of intense picosecond laser pulses

The generation of relativistic electron beams in hollow glass capillaries is investigated using a picosecond laser system. A plasma is formed in a capillary due to the ablation of its inner walls by a specially formed pre-pulse. Electron beams with an opening angle of ∼40 mrad, exponential energy spectrum with maximum energy about 20 MeV, and a total charge of ∼0.2 nC are experimentally detected.

Fiber-solid hybrid end-pumped Nd:YVO4 picosecond amplifier with high beam quality

In recent years, high-brightness picosecond lasers have been widely used in high-end precision processing, spectroscopy and high harmonic generation. To obtain higher power and excellent beam quality, it is an ideal solution to add a high-gain amplifier to the back end of the high-stability picosecond fiber or solid seed. In this article, a fiber-solid hybrid end-pumped Nd:YVO4 picosecond laser system with high beam quality is demonstrated. The influence of the self-developed picosecond fiber seed output characteristics on solid amplifiers has been studied in detail, including the energy, repetition rate and spectrum. After two-stage traveling wave amplifiers, the maximum 155 μJ single pulse energy is obtained with 20 kHz repetition rate, and the corresponding peak power reaches 14.9 MW with 10.4 ps pulse duration. Meanwhile, the beam quality factors under the maximum 18.4 W average power are measured to be M x 2 = 1.27 and M y 2 = 1.25, respectively.

Excimer formation dynamics in the isolated tetracene dimer.

The understanding of excimer formation and its interplay with the singlet-correlated triplet pair state 1(TT) is of high significance for the development of efficient organic electronics. Here, we study the photoinduced dynamics of the tetracene dimer in the gas phase by time-resolved photoionisation and photoion imaging experiments as well as nonadiabatic dynamics simulations in order to obtain mechanistic insight into the excimer formation dynamics. The experiments are performed using a picosecond laser system for excitation into the S2 state and reveal a biexponential time dependence. The time constants, obtained as a function of excess energy, lie in the range between ≈10 ps and 100 ps and are assigned to the relaxation of the excimer on the S1 surface and to its deactivation to the ground state. Simulations of the quantum-classical photodynamics are carried out in the frame of the semi-empirical CISD and TD-lc-DFTB methods. Both theoretical approaches reveal a dominating relaxation pathway that is characterised by the formation of a perfectly stacked excimer. TD-lc-DFTB simulations have also uncovered a second relaxation channel into a less stable dimer conformation in the S1 state. Both methods have consistently shown that the electronic and geometric relaxation to the excimer state is completed in less than 10 ps. The inclusion of doubly excited states in the CISD dynamics and their diabatisation further allowed to observe a transient population of the 1(TT) state, which, however, gets depopulated on a timescale of 8 ps, leading finally to the trapping in the excimer minimum.

Development of a single-shot third-order cross-correlator for picosecond laser systems

In this paper we present the development of a near-field single-shot third-order cross-correlator. We present measurements of sub-ps pulses at λ=1055.5nm demonstrating the device has a temporal window of ΔT=36.4 ps and a resolution of δt=91 fs. We also discuss the spectral acceptance and the minimum required operational conditions.

Picosecond high-power 213-nm deep-ultraviolet laser generation using β-BaB2O4 crystal

In this study, we successfully demonstrate the achievement of 1.37 W average power for a picosecond deep ultraviolet (DUV) laser at 213 nm with a 1 MHz repetition rate using β-BaB2O4 (BBO) crystals, which is the highest output power of a 213 nm picosecond laser system with an all-solid-state setup so far. The laser system generates over 1.3 μJ 213-nm pulse energy. The fifth harmonic is generated by sum-frequency generation of the 532 and 355 nm beams based on a “2 + 3” scheme. BBO crystals with lengths of 6, 8, and 10 mm are investigated. Furthermore, the DUV laser system produces a high-beam quality and narrow linewidth output. The DUV system can be stably maintained over 100 h with expanded beam sizes of 532 and 355 nm at 800 mW, and without requiring a change in the positions and temperatures of nonlinear crystals.

Compact 50 W All-Solid-State Picosecond Laser System at 1 kHz

Compact, stable, high-power and high repetition rate picosecond laser systems are excellent sources for optical parametric chirped pulse amplification systems and laser satellite ranging systems. Compared with the traditional complex high-power amplifier, this article reports a compact high-power picosecond laser system at a repetition rate of 1 kHz based on Nd:YAG bulk crystal. The thermal lens effect limits the regenerative amplifier to directly output higher energy. For this reason, multi-stage traveling-wave amplifiers are usually used to gradually increase the laser pulse energy. So as to achieve a compact structure, a regenerative amplifier that can output higher power at 1 kHz is designed in the laser system. The regenerative amplifier can output the power of 6.5 W at the pump power of 41.5 W; the beam quality of M2 factor was about 1.3. A more flexible thermal depolarization compensation structure is applied in the side-pumped amplifier, which can effectively compensate for thermal lens effect and thermal depolarization at different pump powers. Finally, the laser pulse can achieve an output power higher than 50 W at 1 kHz after passing through an end-pumped traveling-wave amplifier and a side-pumped traveling wave amplifier.

Effect of biomimetic fishbone-patterned copper tubes on pool boiling heat transfer

The effect of laser-textured copper surfaces on pool boiling heat transfer in copper tubes was experimentally investigated by using deionized water as a working fluid under ambient environmental conditions. The picosecond laser system was used to apply fishbone patterns on cylindrical copper surfaces. All pool boiling experiments were performed using a saturated working fluid, and the heat flux was up to 426 kW/m2 in these experiments. The heat transfer coefficient of laser-textured dense fishbone sample exhibited a factor up to 1.12 at the highest evaluated heat flux. Bubble dynamics were studied using images recorded using high-speed cameras under different heat flux regimes. In addition, the effect of laser-textured surfaces on the temperature distribution during pool boiling along cylindrical surfaces was analyzed.

Effects of difference in wettability level of biphilic patterns on copper tubes in pool boiling heat transfer

This study experimentally investigated pool boiling heat transfer on copper tubes for superhydrophilic surfaces with square patterns of different wettability levels. Deionized (DI) water was used as a working fluid. A silica-based coating mechanism and the picosecond (ps) laser system were combined to fabricate samples with different surface wettability levels. The contact angle values of four types of samples were in the range 0°–150°. The boiling experiments were conducted under ambient conditions up to a maximum heat flux regime of 418 kW/m2 and a saturated working fluid. Compared with the homogeneous plain copper surface, the heat transfer coefficient of the biphilic surface with hydrophobic patterns was enhanced up to 1.16, whereas that with superhydrophobic patterns decreased to 0.83 at the highest evaluated heat flux (418 kW/m2) because surface wettability led to different bubble dynamics. Bubble dynamics, on different samples were analyzed through high-speed imaging at three intervals of heat flux.

Novel method to reduce the transverse sensitivity of granular thin film strain gauges by modification of strain transfer

Abstract. Strain gauges based on polyimide carrier foils and piezoresistive granular thin films are highly sensitive to strain. Unlike conventional metal foil, granular film strain gauges also have a pronounced sensitivity to strain acting in the transverse direction. A novel method that allows for the modification of the strain transfer is proposed and proven experimentally. The method is based on the creation of stand-alone polyimide paths, on top of which the piezoresistive thin film is located. In this way, the granular film hardly receives any transverse strain; hence, the transverse sensitivity is drastically reduced. A picosecond laser system can be used for both patterning of the thin film and for controlled ablation of polyimide in order to generate well-defined high path structures. The working principle of the method is demonstrated by simulation, followed by an experimental verification using measurements of the transverse gauge factor. Furthermore, the output signal of force transducers may be increased using granular thin film strain gauges of reduced transverse sensitivity.

Experimental investigation of inner bubble dynamics during water droplet evaporation from heated surfaces with different roughness and wettability levels

In this study, sol-gel method and picosecond laser system were used to create surfaces with various roughness and wettability levels. The ranges of contact angle and surface roughness were 0°–125° and 0.121–0.356 μm, respectively. The influence of surface roughness and wettability on bubble dynamics was experimentally investigated by observing droplet evaporation on heated surfaces. The results revealed that not only the surface temperature but also surface characteristics affected bubble behavior and resulted in different evaporation efficiencies. Droplets evaporated most rapidly on the laser-textured copper surface because of its hydrophobicity and enhanced surface roughness, which led to improved liquid–vapor heat transfer in active bubbles behavior. By contrast, silica-coated surfaces exhibited the lowest droplet evaporation efficiency. This evaporation efficiency was attributed to the hydrophilic wetting state and high bubble covering area, which hindered the heat transfer from the heated surface to the liquid droplet. The overall evaporation time on the laser-textured surface was approximately 77% shorter than that on other surfaces for the highest evaluated surface temperature. In addition, the experimental results of the overall evaporation time were compared with the results of the prediction model. With the increase in the temperature of the surface, the hydrophobic wetting state increased, which led to larger differences between the model and experimental results.

Application of a Holed Cathode and Anode Preparedwith a Picosecond Pulsed Laser for Lithium Ion Batteries (1)~ Performance of Holed Cathodes with Solid-State Electrolytes ~

Recently, we have reported that the porous current collector could be produced with a pico-second pulse laser system and that graphite electrodes prepared with porous Cu current collectors improved the rate of Li+-pre-doping reaction in the laminated graphite electrodes [1-3]. In this study, in order to speed up the rate of the pre-doping reaction more, the porous graphite electrodes were prepared by directly opening the holes on the surface of graphite electrodes with a picosecond laser (Fig. 1). In the cell composed of laminated porous graphite electrodes (Fig. 2) and a lithium metal, the Li+-doping reaction proceeded much faster than in the cells of the graphite electrodes prepared with porous current collectors and a Li metal. In addition, the results of electrochemical impedance spectroscopy suggested that the transfer of Li+ ions though the holes on the graphite electrodes was a rate determining step of the doping reaction of Li+ to laminated graphite electrodes and that the decrease in the hole diameter at the constant of opening rate of holes on the graphite electrodes cased the reduction of resistance for Li+ ions, resulting in shortening the time for completing the doping reaction of Li+ ions. Figure 1

A novel fabrication of superhydrophobic surfaces on aluminium substrate by picosecond pulsed laser

Superhydrophobic surfaces have emerged because of their unique properties like corrosion resistance, self-cleaning, anti-icing and being anti-bacterial. A simplistic and highly effective ultra-fast laser technology was used to fabricate superhydrophobic surface on aluminum substrate. Compared to other laser systems, picosecond laser systems have smaller thermal affected area on the aluminum substrate. They also offer high efficiency, not as much of waste materials and cover enormous areas for mass production. Tilted groove patterns of various angles with respect to horizontal were textured on the substrate by using picosecond laser pulses. The laser parameters, such as hatching distance (HD) and scanning speed (SS), can be varied by keeping the laser power as constant for the various tilted angle of the groove pattern. The textured surfaces were initially super hydrophilic when kept in polyethylene zip lock cover and which also exhibits super hydrophobicity of maximum 155.5° when observed after 15 days. The morphology of surface was characterized by scanning electron microscope, EDX and X-ray diffraction.

Maskless, rapid manufacturing of glass microfluidic devices using a picosecond pulsed laser

Conventional manufacturing of glass microfluidic devices is a complex, multi-step process that involves a combination of different fabrication techniques, typically photolithography, chemical/dry etching and thermal/anodic bonding. As a result, the process is time-consuming and expensive, in particular when developing microfluidic prototypes or even manufacturing them in low quantity. This report describes a fabrication technique in which a picosecond pulsed laser system is the only tool required to manufacture a microfluidic device from transparent glass substrates. The laser system is used for the generation of microfluidic patterns directly on glass, the drilling of inlet/outlet ports in glass covers, and the bonding of two glass plates together in order to enclose the laser-generated patterns from the top. This method enables the manufacturing of a fully-functional microfluidic device in a few hours, without using any projection masks, dangerous chemicals, and additional expensive tools, e.g., a mask writer or bonding machine. The method allows the fabrication of various types of microfluidic devices, e.g., Hele-Shaw cells and microfluidics comprising complex patterns resembling up-scaled cross-sections of realistic rock samples, suitable for the investigation of CO2 storage, water remediation and hydrocarbon recovery processes. The method also provides a route for embedding small 3D objects inside these devices.

Highly efficient tunable picosecond deep ultraviolet laser system for Raman spectroscopy.

We present a narrowband laser system tunable from 219 to 236 nm for deep ultraviolet (DUV) Raman spectroscopy. The demonstrated laser system produces 6.7 ps nearly transform-limited pulses with energy up to 0.36 µJ at 100 kHz repetition rate. The system consists of a two-stage optical parametric amplifier (OPA) of a narrowband continuous wave diode laser and subsequent frequency conversion to the DUV radiation. We achieve more than 300 mW in the signal wave using ${{\rm LiB}_3}{{\rm O}_5}$LiB3O5 (LBO) and ${{\rm BaB}_2}{{\rm O}_4}$BaB2O4 (BBO) crystals, with the total 2.7 W pump after the two-stage OPA. We reach 12% conversion efficiency of the OPA signal wave into the DUV radiation using type-I phase matching in the BBO crystal. Finally, we demonstrate the applicability of the system for DUV Raman spectroscopy by collecting a high dynamic range, high spectral resolution spontaneous Raman spectrum of air.

A high-beam-quality, high-pulse-energy picosecond laser system for high precision ultra-remote laser ranging

A high-beam-quality, high-pulse-energy picosecond laser system for high precision ultra-remote laser ranging