Picosecond Laser System Research Articles

BioCARS: a synchrotron resource for time-resolved X-ray science

BioCARS, a NIH-supported national user facility for macromolecular time-resolved X-ray crystallography at the Advanced Photon Source (APS), has recently completed commissioning of an upgraded undulator-based beamline optimized for single-shot laser-pump X-ray-probe measurements with time resolution as short as 100 ps. The source consists of two in-line undulators with periods of 23 and 27 mm that together provide high-flux pink-beam capability at 12 keV as well as first-harmonic coverage from 6.8 to 19 keV. A high-heat-load chopper reduces the average power load on downstream components, thereby preserving the surface figure of a Kirkpatrick-Baez mirror system capable of focusing the X-ray beam to a spot size of 90 µm horizontal by 20 µm vertical. A high-speed chopper isolates single X-ray pulses at 1 kHz in both hybrid and 24-bunch modes of the APS storage ring. In hybrid mode each isolated X-ray pulse delivers up to ~4 × 10(10) photons to the sample, thereby achieving a time-averaged flux approaching that of fourth-generation X-FEL sources. A new high-power picosecond laser system delivers pulses tunable over the wavelength range 450-2000 nm. These pulses are synchronized to the storage-ring RF clock with long-term stability better than 10 ps RMS. Monochromatic experimental capability with Biosafety Level 3 certification has been retained.

Picosecond laser system with 30-W average power via cavity dumping and amplifying

We present a picosecond laser system with high energy by technologies of cavity dumping and amplifying. Firstly, pulses with 10 ps and ∼520 nJ were obtained by cavity-dumped mode-locked laser at 10 kHz repetition rate. Secondly those pulses were seeded into a side-pumped regenerative amplifier (RA). Then pulses output from the regenerative amplifier were amplified by two four-pass post amplifiers. From the laser system pulses with an average power of 30 W corresponding to 3 mJ pulse energy were achieved with the pulse-width of 25.4 ps at repetition rate of 10 kHz.

Laser ablation of CFRP using picosecond laser pulses at different wavelengths from UV to IR

Laser processing of carbon fibre reinforced plastics (CFRP) has a great industrial relevance for high performance structural parts in airplanes, machine tools and cars. Through-holes drilled by nanosecond laser pulses show thermal induced molten layers and voids. Recently, picosecond lasers have demonstrated the ability to drill high-efficient and high-quality rivet through-holes. In this paper a high-power picosecond laser system operating at different wavelengths (355nm, 532nm and 1064nm) has been used for CFRP ablation experiments to study the influence of different laser parameters in terms of machining quality and processing time.

Ultra: A Unique Instrument for Time-Resolved Spectroscopy

We report the development of a high-sensitivity time-resolved infrared and Raman spectrometer with exceptional experimental flexibility based on a 10-kHz synchronized dual-arm femtosecond and picosecond laser system. Ultrafast high-average-power titanium sapphire lasers and optical parametric amplifiers provide wavelength tuning from the ultraviolet (UV) to the mid-infrared region. Customized silicon, indium gallium arsenide, and mercury cadmium telluride linear array detectors are provided to monitor the probe laser intensity in the UV to mid-infrared wavelength range capable of measuring changes in sample absorbance of ΔOD ~ 10(-5) in 1 second. The system performance is demonstrated for the time-resolved infrared, two-dimensional (2D) infrared, and femtosecond stimulated Raman spectroscopy techniques with organometallic intermediates, organic excited states, and the dynamics of the tertiary structure of DNA.

Microdrilling in steel using ultrashort pulsed laser beams with radial and azimuthal polarization

A linear to radial and/or azimuthal polarization converter (LRAC) has been inserted into the beam delivery of a micromachining station equipped with a picosecond laser system. Percussion drilling and helical drilling in steel have been performed using radially as well as azimuthally polarized infrared radiation at 1030 nm. The presented machining results are discussed on the basis of numerical simulations of the polarization-dependent beam propagation inside the fabricated capillaries.

Two-Photon Polymerization of a Polymer-Ceramic Hybrid Material with a Low-Cost Nd:YAG Laser: Preliminary Resolution Study and 3D Fabrication

This paper reports the microfabrication of a polymer-ceramic hybrid material (Ormocomp®) with a low cost Nd:YAG picosecond laser system. Both the process resolution and the fabrication of three-dimensional (3D) microobjects were studied. Microstructures were fabricated on microscope slides with a moving xyz platform and a real-time process monitoring system by tracking the contours of the structure with the laser focus, followed by rinsing away the unpolymerized resin. The evaluation of the process resolution was based on the scanning electron microscope (SEM) images of socalled voxels and polymer lines. The dimensions of the produced structures varied greatly depending on the laser focus position and the process parameters used. The minimum achievable feature size was found to be approximately 1 μm. Microcylinders, cones and cone arrays were fabricated and studied with SEM imaging. The biocompatibility of the Ormocomp ®-photoinitiator combination was also demonstrated with human embryonic stem cell-derived neuronal cells. The fabricated structures could in the future be utilized in cell culture and drug delivery applications.

The methods of RF phase locked loops for active mode‐locking picosecond laser with different repetition rates

AbstractThe novel methods of RF phase locked loops for picosecond laser system with four repetition rate 402.5 MHz, 1.792 GHz, 10 GHz, and 40 GHz have been presented in this article. Double loop integration parameter adjustment has been used to provide suitable feedback optical‐RF signal controlling. Four kinds of RF phase locked loops ways for different repetition rates' picosecond laser system have been introduced with complete configuration and analysis. To different microwave frequency range, different PLL method has been adopted to fit the demand of reducing phase noise and jitters while to get better pulse output feature. Data are obtained from experiments to make measurement of the pulse output performance and phase noise. Agreement of the theoretical and experimental results confirms the applicability of these phase locked loops design methods and theoretical analysis given in this article. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2886–2892, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24803

A picosecond IR laser system with tunable wavelength, based on a hybrid CO_2 laser

This paper describes a picosecond laser system based on a hybrid CO2 laser, using optically controlled semiconductor switches with a pulse width from 100 ps to 300 ns, followed by conversion of the radiation in nonlinear crystals by means of second-harmonic generation. Silver selenogallate AgGaSe2 and zinc germanium diphosphide ZnGeP2 are used as nonlinear crystals. Two-stage conversion of the radiation of a picosecond CO2 laser with wavelength 9.4-10.6 μm into laser radiation with wavelengths 4.7-5.3 μm is carried out in the apparatus with an efficiency of 0.3%-0.5%, while 4.7-5.3-μm radiation is converted into 2.4-2.65-μm radiation with an efficiency of 8%. The overall conversion efficiency is 4×10−4 or 0.04% for an output pulse energy up to 35 μJ.

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.

Optical unit of Laser-Electron X-ray Generator designed for medical applications

A design of optical unit for pulsed Laser Electron X-Ray Generator is proposed. The generator provides the exposure 0.1–1 ms at frame rate 30 Hz. It consists of a completely passive circulator based on second harmonic generation and a picosecond laser system which includes a master oscillator, pulse picking systems and amplifiers. To specially arrange the output time structure, two master oscillators controlled with optoelectronic negative feedback are proposed and tested. The first system allows to obtain regular bursting with period from 25 to 75 cavity round trips smoothly varied by the voltage applied to the Pockels cell based on TaLiO 3 crystal. In the second laser system secondary electro-optic effect in a DKDP crystal of Pockels cell is used and the period of regular bursts is varied discretely from 7.8 μ s down to 0.52 μ s .

High Energy Picosecond Lasers: Ready for Prime Time

AbstractHigh‐pulse energy picosecond laser systems provide industrial‐level reliability combined with the performance features required for many ultrafast material processing applications. Current diodepumped solid‐state systems provide pulse energies into the 100's of microjoules at 1064 nm wavelength and pulse widths of approximately 10 picoseconds, which allows effective “cold” ablation of most materials with high efficiency. Average power of these systems is scalable up to 50 W and will further increase into the multi‐100 W range, allowing for very high speed picosecond micromachining.This article first reviews the basics of picosecond micromachining, gives a short perspective on the development of these lasers over the last few decades, then summarizes their current performance. We review some of the applications that are enabled with these lasers, before we discuss future developments in this rapidly changing field.

Development of a temporal filtering technique for suppression of interferences in applied laser-induced fluorescence diagnostics

A temporal filtering technique, complementary to spectral filtering, has been developed for laser-induced fluorescence measurements. The filter is applicable in cases where the laser-induced interfering signals and the signal of interest have different temporal characteristics. For the interfering-signal discrimination a picosecond laser system along with a fast time-gated intensified CCD camera were used. In order to demonstrate and evaluate the temporal filtering concept two measurement situations were investigated; one where toluene fluorescence was discriminated from interfering luminescence of an aluminum surface, and in the other one Mie scattering signals from a water aerosol were filtered out from acetone fluorescence images. A mathematical model was developed to simulate and evaluate the temporal filter for a general measurement situation based on pulsed-laser excitation together with time-gated detection. Using system parameters measured with a streak camera, the model was validated for LIF imaging of acetone vapor inside a water aerosol. The results show that the temporal filter is capable of efficient suppression of interfering signal contributions. The photophysical properties of several species commonly studied by LIF in combustion research have been listed and discussed to provide guidelines for optimum use of the technique.

Picosecond Raman spectroscopy with a fast intensified CCD camera for depth analysis of diffusely scattering media

A spectroscopic depth profiling approach is demonstrated for layers of non-transparent, diffusely scattering materials. The technique is based on the temporal discrimination between Raman photons emitted from the surface and Raman photons originating from a deeper layer. Excitation was carried out with a frequency-doubled, 3 ps Ti:sapphire laser system (398 nm; 76 MHz repetition rate). Time-resolved detection was carried out with an intensified CCD camera that can be gated with a 250 ps gate width. The performance of the system was assessed using 1 mm and 2 mm pathlength cuvettes with powdered PMMA and trans-stilbene (TS) crystals, respectively, or solid white polymer blocks: Arnite (polyethylene terephthalate), Delrin (polyoxymethylene), polythene (polyethylene) and Teflon (polytetrafluoroethylene). These samples were pressed together in different configurations and Raman photons were collected in backscatter mode in order to study the time difference in such media corresponding with several mm of extra net photon migration distance. We also studied the lateral contrast between two different second layers. The results demonstrate that by means of a picosecond laser system and the time discrimination of a gated intensified CCD camera, molecular spectroscopic information can be obtained through a turbid surface layer. In the case of the PMMA/TS two-layer system, time-resolved detection with a 400 ps delay improved the relative intensity of the Raman bands of the second layer with a factor of 124 in comparison with the spectrum recorded with a 100 ps delay (which is more selective for the first layer) and with a factor of 14 in comparison with a non-gated setup. Possible applications will be discussed, as well as advantages/disadvantages over other Raman techniques for diffusely scattering media.

Generation of Fiber Tunable High-power Picosecond Laser Pulse

A fiber tunable high-power picosecond laser system has been for the first time demonstrated. A gain switch semiconductor laser diode was introduced as seed source, and a multi-stage single mode Yb-doped fiber amplifier was combined with a single mode double-clad Yb-doped fiber amplifier to construct the amplification system. High stability and good beam quality pulses with 1MHz tunable repetition rate, 3W average power, 90ps pulse duration, and central wavelength tunable from 1053 nm to 1073 nm were generated. The completely fiber integrated approach has the potential to be scaled to significantly higher average powers.

Replica molding of picosecond laser fabricated Si microstructures

This work demonstrates the fast generation and rapid replication of laser-fabricated three-dimensional conical microstructures on single-crystalline silicon. Large areas containing Si structures are fabricated by fast scanning of the focussed laser beam of a high-power, high repetition rate infrared picosecond laser system over the Si surface, in the presence of SF6. Furthermore, the possibility of replicating the initial spiked morphology on other materials is demonstrated by polydimethylsiloxane molding in vacuum. Results showing the successful transfer of the initial conical morphology on the photocurable resist material ORMOCER (an organically modified ceramic) are presented. The combination of laser-based methods and standard replication technology may open up interesting prospects for the fast and efficient transfer of three-dimensional patterns over a wide range of materials.

High quality, high power pico-second laser system with a phase conjugate mirror

We developed a high quality (near diffraction-limited) and high power (25W) pico-seocnd (-8ps) laser system with a phase conjugate mirror. This laser system should be a promising laser sourcefor nonlinear microscopy, multi-photon spectroscopy, mid-infrared as well as ultra-violetgeneration.

Effects of Gamma and Heavy Ion Damage on the Impulse Response and Pulsed Gain of a Low Breakdown Voltage Si Avalanche Photodiode

Effects of displacement and ionization damage on the impulse response of a high-bandwidth low breakdown voltage Si Avalanche Photodiode was investigated using a picosecond laser system. Damage was generated using either Co60 gamma-irradiation or by scanning the device with an MeV ion microbeam. No shift in the impulse response characteristics and gain was observed for gamma doses as high as 100 kGy(Si). However, dark current measurements for irradiations with biases close to typical operating levels, exhibited enhanced ionization damage orders of magnitude higher than for no bias. Displacement damage introduced by the microbeam was used to differentiate between ionization damage in the guard ring isolation oxide and bulk damage. The absence of any marked change in the impulse response is discussed, as are possible mechanisms for the enhanced ionization damage

All-Fiber Picosecond Laser System at 1.5 $\mu$m Based on Amplification in Short and Heavily Doped Phosphate-Glass Fiber

Amplification of ultrashort pulses in doped fibers is limited by an onset of nonlinear effects in the fiber. At the 1.5-mum wavelength, single-mode fibers typically have anomalous dispersion. The self-phase modulation combined with dispersion leads to instability of multinanojoule pulses in such fibers. Various techniques developed to amplify pulses beyond the nonlinearity limit typically rely on a delicate balance between dispersive and nonlinear effects in different parts of the laser system. We report a simple all-fiber alternative to these complex techniques that utilizes a rapid amplification of pulses in a short and heavily doped phosphate-glass active fiber. In our preliminary experiments, picosecond pulses at 1.5 mum generated by a passively mode-locked fiber oscillator at a repetition rate of 70 MHz are amplified in a 15-cm-long heavily Er-Yb codoped fiber amplifier to the average output power of 1.425 W. The pulse energy and peak power reach 20.4 nJ and 16.6 kW, respectively, while the pulse distortion is minimal in both temporal and spectral domains. Further power up-scaling is possible by using active phosphate fiber with a large mode area, in the amplifier stage

Energy Transfer in the d3Πg−a3Πu (0−0) Swan Bands of C2: Implications for Quantitative Measurements

Energy transfer effects on dicarbon (C2) d3Pi(g) <-- a3Pi(u) laser-induced fluorescence (LIF) spectra in fuel-rich acetylene atmospheric-pressure flames have been studied using a combination of two different two-dimensional techniques. Measurements using a picosecond laser system in conjunction with a streak camera allowed determination of typical fluorescence lifetimes of levels in the d state and of population changes introduced by rotational energy transfer (RET) and by state-dependent quenching. Excitation-emission spectroscopy yielded two-dimensional maps containing all excitation and all emission spectra in the spectral ranges between 19 340 and 20 150 cm(-1) (excitation) and from 546 to 573 nm (emission) and allowed unambiguous assignment of all transitions in this spectral region. Our measurements show a comparatively long quenching lifetime (around 2 ns) and dominant effects of energy transfer on shape and intensity of the acquired spectra (90% of the fluorescence stems from levels populated by ET). A pronounced dependence of the total RET on the quantum number of the initially excited state is observed. Vibrational energy transfer (VET) is significantly weaker (only 5% contribution for excitation in the v' = 1 level). Implications for quantitative concentration measurements are discussed, and exemplary spatially resolved profiles in a well-characterized low-pressure propene flame are presented.

Low-loss Type II waveguide writing in fused silica with single picosecond laser pulses

A new domain of rapid waveguide writing with non-overlapping pulses of a 1-kHz ultrashort laser is demonstrated to produce low loss waveguides in fused silica glass. This new regime is distinguishable in two ways from traditional approaches in laser waveguide writing. First, an examination of a wide 50-fs to 5-ps range of pulse duration shows the lowest loss waveguides to form in a narrow 1.0 +/- 0.2 ps window that significantly exceeds the 50 - 200 fs duration reported as optimal in other studies. Second, an unusually high scan speed of 1.0 +/- 0.2 mm/s points to a novel Type-II photosensitivity mechanism for generating low-loss refractive index structures. The waveguides comprise of an array of nearly isolated single-pulse interaction volumes that sharply contrast with the high exposures of tens to thousands of overlapping laser pulses typically applied along a slowly moving focal volume. A minimum propagation loss of ~0.2 dB/cm and a slightly asymmetric mode diameter of ~9 mum is reported for 633-nm light. The low loss waveguides fabricated with picosecond pulses enables 3-D photonics circuit fabrication with simpler and lower cost picosecond laser systems.