High Repetition Rate Picosecond Laser Research Articles

Efficient milling and cutting of borosilicate glasses through a thin flowing water film with a picosecond laser

Direct laser ablation allows high-quality processing, precision, and cutting of complex shapes. Unfortunately, this technology is usually not considered as the primary candidate for cutting and milling of glasses due to low processing speeds. Thus, laser-based rear side drilling and crack generation techniques are chosen instead. However, we report on the milling and cutting of borosilicate glass plates with high average power and high pulse repetition rate picosecond laser. We optimised laser processing parameters for the efficient direct material ablation and employed water-assisted ablation to improve the ablation efficiency and the cutting speed of borosilicate glasses. The laser process was realised through a thin flowing water film, which was formed by spraying water mist on the surface of the workpiece. Firstly, we characterised thin water film parameters, such as film thickness, flow velocity, and defined a working area with constant processing conditions. Next, we optimised laser processing parameters for both processing environments: ablation through the thin water film and in air. Under optimal parameters, ablation through the thin water film was much more effective, increasing the cutting speed of 420 μm thick glass plates nearly ten times – from 0.52 to 5 mm/s. Furthermore, the morphology of the cuts was improved as well: cut wall roughness and edge chipping were reduced, spatter deposition was avoided in the vicinity of the cut. We investigated the milling of 130 to 1700 μm wide and 50 to 500 μm deep grooves with a maximum depth-to-width ratio of 3.8. Findings revealed that the ablation efficiency increase provided by the water layer did not depend on the depth or the width of the groove and remained constant. Therefore, it became possible to predict the ablation efficiency through the thin water film by knowing the ablation efficiency in air and an absolute ablation efficiency difference between two processing environments. • Efficient borosilicate glass milling and cutting in the air and through the water film was conducted with a picosecond laser. • Optimal laser fluence for efficient glass ablation was 40% higher than in air. • An absolute change in ablation efficiency between two environments did not depend on the transverse dimensions of the groove. • Water film improved ablation efficiency significantly, resulting in nearly 10 times higher cutting speed than in air.

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.

Direct laser writing of graphene films from a polyether ether ketone precursor

Graphene-based micro-supercapacitors exhibit excellent electrochemical performance that can easily meet the energy storage requirements of micro-electronic products. However, the complex preparation and transfer process steps of traditional preparation methods limit their wide application. Direct laser writing can deposit graphene laser-induced graphene (LIG) onto a specific substrate-patterned electrodes. This approach offers great advantages in the preparation of miniature and complex-patterned electrodes, but currently there is a limited choice of precursor materials. In this reported study, biocompatible polyether ether ketone (PEEK) was irradiated using a high repetition rate picosecond laser to produce graphene. Various photothermal and photochemical reactions were involved in the one-step conversion of PEEK into a film comprised of a several layers (3–4) of graphene. The electrochemical testing of a three-electrode system containing this novel graphene showed that LIG had a specific capacitance of 20.4 mF cm−2 at a scan speed of 10 mV s−1, and the capacitance was reversibly maintained with 89.37% retention of the initial capacitance after 5000 cycles. The novel LIG with higher specific capacitance and cycle stability has great potential for use in energy storage micro-devices.

Picosecond Laser based Additive Manufacturing of Hydroxyapatite Coatings on Cobalt Chromium Surfaces

We report high repetition rate picosecond laser based additive manufacturing process to coat nanoscale rough hydroxyapatite (HA) on cobalt chromium plates (CoCr). Nanoscale rough coatings of hydroxyapatite are desirable as they mimic the naturally formed hydroxyapatite and in addition provide very high surface area and surface roughness, which leads to better cell adhesion and cell-matrix interaction. Nanoscale HA powders are synthesized using sol-gel procedure and ball milling. Ball-milled powders are suspended in volatile solvents and coated on the CoCr surface using picosecond laser irradiation. The chemical composition and morphology of the coated material was characterized using electron microscopy. The laser-assisted fusion process results in HA coatings that have hierarchical surface roughness down to nanometer scale which may enhance the biocompatibility of the CoCr implants.

SESAM无损伤运转的大功率高重频皮秒激光器

SESAM无损伤运转的大功率高重频皮秒激光器

Rapid micromachining of high aspect ratio holes in fused silica glass by high repetition rate picosecond laser

We present multiple methods of high aspect ratio hole drilling in fused silica glass, taking advantage of high power and high repetition rate picosecond lasers and flexible beam delivery methods to excise deep holes with minimal collateral damage. Combinations of static and synchronous scanning of laser focus were explored over a range of laser repetition rates and burst-train profiles that dramatically vary laser plume interaction dynamics, heat-affected zone, and heat accumulation physics. Chemically assisted etching of picosecond laser modification tracks are also presented as an extension from femtosecond laser writing of volume nanograting to form high aspect ratio (77) channels. Processing windows are identified for the various beam delivery methods that optimize the laser exposure over energy, wavelength, and repetition rate to reduce microcracking and deleterious heating effects. The results show the benefits of femtosecond laser interactions in glass extend into the picosecond domain, where the attributes of higher power further yield wide processing windows and significantly faster fabrication speed. High aspect ratio holes of 400 μm depth were formed over widely varying rates of 333 holes per second for mildly cracked holes in static-focal positioning through to one hole per second for low-damage and taper free holes in synchronous scanning.

Role of thermal ionization in internal modification of bulk borosilicate glass with picosecond laser pulses at high repetition rates

We study the roles of thermal ionization and electronic damage in the internal modification of bulk borosilicate glass by high repetition rate picosecond laser pulses. Laser-induced plasma generation, nonlinear energy deposition and steady temperature distribution are numerically analyzed. The simulated modified regions show good agreement with the experimental results, thereby revealing the roles of thermal damage and electronic damage in the internal modification. While the elliptical outer structure is recognized as the molten region, we found that the teardrop-shaped inner structure is the damaged zone caused by high-density free-electrons. In the formation of the inner structure, cascade ionization is seeded by thermal ionization instead of multi-photon ionization and dramatically increases the free-electron density to the damage threshold. The contour of the inner structure is found to be corresponding to a characteristic isotherm of around 3000 ~4000 °C.

Ultrashort picosecond laser processing of micro-molds for fabricating plastic parts with superhydrophobic surfaces

High repetition rate picosecond laser pulses are used to form hierarchical structures on titanium in air for the development of superhydrophobic surfaces. The treated titanium surfaces are used as masters for polymer replicas in soft lithography. The complex topography of the master has been shown to successfully transfer to UV-curable polymer replicas without significant change in morphology or wetting characteristics. This approach demonstrates a low-cost, high-efficiency process combining rapid picosecond laser-based fabrication and micro-replication technology for the reproduction of widely used functional plastic parts.

Direct Waveguide Writing with High Energy High Repetition Rate Picosecond Laser Pulses

Abstract Direct femtosecond pulse laser waveguide writing based on laser induced localized modification of the refractive index of bulk glass can be a versatile fabrication method for many micro applications. Although the method's potentials have been realized its application is still rather limited, either due to the slow writing speeds caused by low laser pulse repetition rates of amplified systems or due to the shallow structuring depths restricted by low pulse energies of nonamplified lasers. In this work we investigate the direct waveguide writing process using a picosecond laser that allows fast and deep waveguide writing due to high pulse energies available at high pulse repetition frequencies.

Picosecond-Laser Structuring of Thin Films for CIGS Solar Cells

Interest in complex multilayered CuInxGa(1-x)Se2 solar cells has increased recently because of unique combination of factors such as low manufacturing cost and high photovoltaic conversion efficiency. The efficiency of the thin-film solar cells with a large active area might be maintained making series interconnects in order to reduce photocurrent in thin films and resistance losses. Laser technologies are a promising method to accomplish the scribing processes. Lasers with the picosecond pulse duration were applied in structuring of conducting, semi-conducting and isolating films in the complex multilayered Cu(InGa)Se2 (CIGS) solar cells deposited on the polyimide substrate. The wavelength of laser radiation was adjusted depending on optical properties both of the film and the substrate. A narrow processing window of laser fluence and pulse overlap was estimated to remove the molybdenum back-contact off the substrate. The selective removal of ITO and CIGS layers was achieved with the 355 nm irradiation without a significant damage to the underneath layers in the ITO/CIGS/Mo/PI solar cell system. The 355 nm wavelength was also found to be favorable for the P3 scribing process in the ZnO/CIGS/Mo/PI solar cell system. High repetition rate picosecond lasers with a short pulse duration offer new possibilities for high quality and efficiency scribing.

Diffractive multi-beam surface micro-processing using 10 ps laser pulses

A high repetition rate picosecond laser system is combined with a spatial light modulator (SLM) for diffractive multiple beam processing. The effect of the zero order beam is eliminated by adding a Fresnel zone lens (FZL) to defocus the un-diffracted beam at the processing plane. Chromatic dispersion, which is evident with a large bandwidth femtosecond pulses leading to the problem of distorted hole shape is eliminated due to the much narrower spectral bandwidth, ∼0.1 nm at 10 ps pulselength, resulting in highly uniform intensity spots, independent of diffraction angle. In addition, high-throughput processing is demonstrated by combining the high power laser output, 2.5 W at λ ≈ 1064 nm and fast repetition rate, f ≈ 20 kHz with P > 1.2 W diffracted into 25 parallel beams. This has the effect of creating an “effective” repetition rate of 500 kHz without restrictive scan speeds.

Production of Nanoparticles with High Repetition Rate Picosecond Laser

The fabrication of silver and gold nanoparticle colloids using the picosecond (10 ps) laser ablation in liquids was studied. The maximum productivity of 8.6 µg/s nanoparticles was achieved with the 10 ps-laser pulses at high pulse energy (110 µJ) and the repetition rate of 50 kHz. A special stirred flow chamber was constructed in order to improve reproducibility and generation speed of nanopar- ticles in flowing liquid during the ps-laser ablation.

Patterning of ITO Layer on Glass with High Repetition Rate Picosecond Lasers

New high repetition rate picosecond lasers offer possibility for high efficiency structuring of transparent conductors on glass and other substrates. The results of ablation of the indium-tin oxide (ITO) layer on glass with picosecond lasers at various wavelengths are presented. Laser radiation initiated ablation that formed trenches in ITO. Profile of the trenches was analyzed with a phase contrast optical microscope, a stylus type profiler, SEM and AFM. Clean removal of the ITO layer with the 266 nm radiation was observed when laser fluence was above the threshold of 0.20 J/cm, while for the 355 nm radiation the threshold was higher, above 0.46 J/cm. The glass substrate was damaged in the area where the fluence was higher than 1.55 J/cm. The 532 nm radiation allowed getting well defined trenches, but a lot of residues in the form of dust were generated on the surface. Use of UV laser radiation with fluences close to the ablation threshold made it possible to minimize the recast ridge formation and surface contamination during the process. The latter was confirmed by the scanning Auger spectroscopy. The processing speed of up to 0.5 m/s was achieved when using high repetition rate picosecond lasers in the UV range.

Patterning of indium–tin oxide on glass with picosecond lasers

The results of patterning of the indium–tin oxide (ITO) film on the glass substrate with high repetition rate picosecond lasers at various wavelengths are presented. Laser radiation initiated the ablation of the material, forming grooves in ITO. Profile of the grooves was analyzed with a phase contrast optical microscope, a stylus type profiler, scanning electron microscope (SEM) and atomic force microscope (AFM). Clean removal of the ITO film was achieved with the 266 nm radiation when laser fluence was above the threshold at 0.20 J/cm 2, while for the 355 nm radiation, the threshold was higher, above 0.46 J/cm 2. The glass substrate was damaged in the area where the fluence was higher than 1.55 J/cm 2. The 532 nm radiation allowed getting well defined grooves, but a lot of residues in the form of dust were generated on the surface. UV radiation with the 266 nm wavelength provided the widest working window for ITO ablation without damage of the substrate. Use of UV laser radiation with fluences close to the ablation threshold made it possible to minimize surface contamination and the recast ridge formation during the process.

Fast spectroscopy of energy release in nanometric explosives

A nanometric explosive containing 50–200 nm diameter Al particles and a nitrocellulose (NC) oxidizer is studied by high repetition rate picosecond laser ignition combined with time-resolved emission spectroscopy and coherent anti-Stokes Raman spectroscopy (CARS) of ONO 2 stretching of the oxidizer. When the Al aggregates are flash-heated to the boiling point, 2740 K, nitro groups of the oxidizer near each hot aggregate are consumed within 500 ps. A burst of emission that indicates energy release occurs in ∼5 ns. The ignition delay is in the range of 500 ps to 3 ns. The rate-limiting step for energy release at Al-NC hot spots is vibrational relaxation of hot oxidized Al species.

High repetition rate picosecond time-resolved resonance Raman spectroscopy apparatus

A high repetition rate (4.46 kHz) picosecond laser system for time-resolved resonance Raman spectroscopy has been developed with a time resolution of 10 ps. Probe beam pulses are tunable from 550 nm to 655 nm and the pump beam is generated by frequency doubling of the probe beam. Stabilized pulse energies at the sample are >1 mu J/pulse (probe) and >0.2 mu J/pulse (pump). Further tuning is possible using stimulated Stokes-Raman generation in dimethyl sulphoxide (2923 cm-1) which gives up to 35% energy conversion in the first and up to 7% energy conversion in the second Stokes-Raman line.

Erratum: ‘‘High repetition rate picosecond laser system at 1983 nm’’ [Appl. Phys. Lett. 61, 1157 (1992)

The title of this letter was incorrectly printed. The title should read ‘‘High repetition rate picosecond laser system at 193 nm.’’

High repetition rate picosecond laser system at 1983 nm

An efficient scheme to generate picosecond seed pulses at 193 nm for amplification in ArF is described. The amplifier system operates at a repetition rate of 300 Hz providing average output power of 750 mW and pulse duration below 10 ps.

Fluorescence anisotropy decay demonstrates calcium-dependent shape changes in photo-cross-linked calmodulin.

We report dynamic fluorescence anisotropy measurements on the purified dityrosine derivative of calmodulin which was generated during UV irradiation of Ca2+-containing solutions of bovine brain calmodulin [Malencik, D. A., & Anderson, S. R. (1987) Biochemistry 26, 695]. Measurements were made by using a high repetition rate picosecond laser source combined with a microchannel plate photomultiplier. This permits the collection of very low noise anisotropy curves with essentially no convolution artifact. Measured anisotropies at high calcium concentrations are monoexponential, and at 20 degrees C, we recover a correlation time of 9.9 ns. When the temperature is varied from 4.8 to 31.8 degrees C, the recovered correlation time is proportional to the viscosity and inversely proportional to the absolute temperature, behavior expected for the rotational diffusion of a macromolecule whose conformation is independent of the temperature. The correlation time is compared to the theory describing the rotational diffusion of a dumbell. At high calcium concentrations, the cross-linked calmodulin is elongated and has a length equal or nearly equal to that predicted by X-ray crystallographic results. In the absence of calcium, the molecule becomes highly compact and exhibits significant segmental motion. Intermediate calcium ion concentrations result in an intermediate degree of elongation and segmental motion. A small increase in the measured rotational correlation time of calmodulin upon the binding of melittin and mastoparan indicates that these peptides cause no major changes in the elongation of the molecule. When the cross-linked calmodulin is bound to troponin I, the complex rotates as a unit with a single rotational correlation time of 22 ns.