Pulsed Green Laser Research Articles

Low Repetition Rate Subnanosecond Pulse Characteristics of Nd:Lu<inline-formula><tex-math>$_{\bf 0.5}$ </tex-math></inline-formula>Y<inline-formula><tex-math>$_{\bf 0.5}$</tex-math></inline-formula>VO<inline-formula> <tex-math>$_{\bf 4}$</tex-math></inline-formula>/KTP Green Laser With EO and MWCNT

By simultaneously employing electro-optic (EO) modulator and multiwalled carbon nanotube (MWCNT) in a doubly Q-switched mode-locked (QML) Nd:Lu 0.5 Y 0.5 VO 4 /KTP laser, a low repetition rate subnanosecond Nd:Lu 0.5 Y 0.5 VO 4 /KTP green laser with high peak power is presented. Since the repetition rate of this pulsed green laser is controlled by the EO modulator, highly stable laser pulses with low repetition rates of 1-5 kHz are obtained. As the pulse duration of this laser depends on the mode-locked pulse width underneath the Q-switched envelope, subnanosecond green laser pulses with high peak power can be generated. The average output powers, pulse widths as well as peak powers versus incident pump power under different repetition rates are measured. The shortest pulse duration of 415 ps and the highest pulse energy of 424 μJ are obtained at the repetition rate of 1 kHz, corresponding to a peak power of as high as 1022 kW. The experimental results show that the dual-loss modulation technology with EO and MWCNT in QML laser is an efficient method in generating low repetition rate subnanosecond pulse green laser.

A New Method of Fabrication for Multicolor Transparent Thin-film Solar Cell Module

ABSTRACTIn current transparent Si based photovoltaic (PV) module fabrication, green or infrared laser is the most common used band frequency to wipe off the silicon and back contact layer in perpendicular direction of cells. However, this method would result in more power loss than calculation value due to the side effects during the process such as constructional damage of module and shunt effect. A new method is presented here which focus on wiping off more silicon layer by employing green pulsed laser(532 nm wavelength) along the parallel direction of Pattern2, and it shows higher efficiency and more attractive appearance.

Ablation experiment and threshold calculation of titanium alloy irradiated by ultra-fast pulse laser

The interaction between an ultra-fast pulse laser and a material's surface has become a research hotspot in recent years. Micromachining of titanium alloy with an ultra-fast pulse laser is a very important research direction, and it has very important theoretical significance and application value in investigating the ablation threshold of titanium alloy irradiated by ultra-fast pulse lasers. Irradiated by a picosecond pulse laser with wavelengths of 1064 nm and 532 nm, the surface morphology and feature sizes, including ablation crater width (i.e. diameter), ablation depth, ablation area, ablation volume, single pulse ablation rate, and so forth, of the titanium alloy were studied, and their ablation distributions were obtained. The experimental results show that titanium alloy irradiated by a picosecond pulse infrared laser with a 1064 nm wavelength has better ablation morphology than that of the green picosecond pulse laser with a 532 nm wavelength. The feature sizes are approximately linearly dependent on the laser pulse energy density at low energy density and the monotonic increase in laser pulse energy density. With the increase in energy density, the ablation feature sizes are increased. The rate of increase in the feature sizes slows down gradually once the energy density reaches a certain value, and gradually saturated trends occur at a relatively high energy density. Based on the linear relation between the laser pulse energy density and the crater area of the titanium alloy surface, and the Gaussian distribution of the laser intensity on the cross section, the ablation threshold of titanium alloy irradiated by an ultra-fast pulse laser was calculated to be about 0.109 J/cm2.

Optical beam induced current measurements based on two-photon absorption process in 4H-SiC bipolar diodes

Using a pulsed green laser with a wavelength of 532 nm, a duration pulse of ∼1 ns, and a mean power varying between 1 and 100 mW, induced photocurrents have been measured in 4H-SiC bipolar diodes. Considering the photon energy (2.33 eV) and the bandgap of 4H-SiC (3.2 eV), the generation of electron-hole pair by the conventional single photon absorption process should be negligible. The intensity of the measured photocurrents depends quadratically on the power beam intensity. This clearly shows that they are generated using two-photon absorption process. As in conventional OBIC (Optical Beam Induced Current), the measurements give an image of the electric field distribution in the structure under test, and the minority carrier lifetime can be extracted from the decrease of the photocurrent at the edge of the structure. The extracted minority carrier lifetime of 210 ns is consistent with results obtained in case of single photon absorption.

A passively mode-locked intracavity frequency doubled Nd:YVO4 femtosecond green laser based on graphene

By using an atmospheric-pressure chemical vapor deposition (APCVD) method with a C2H2 carbon source, seven-layer graphene films as saturable absorbers are fabricated and transferred to an anti-reflective mirror of 1064 nm wavelength range. Based on this transmission-type graphene saturable absorber mirror (GSAM), a continuous wave (CW) passively mode-locked femtosecond green laser is achieved by 808 nm laser diode (LD) end-pumped Nd:YVO4 crystal and type-I critical phase-matched LBO crystal intracavity frequency doubling for the first time. Stable ultrashort green laser pulses as short as 374 fs are measured with a repetition rate of 71.4 MHz and an average output power of 117 mW at a central wavelength of 531.7 nm.

Impact of the apex of an elongated dielectric tip upon its light absorption properties

This paper discusses the impact of the hemispherical ending of a conical dielectric tip on its optical absorption capabilities. We show that the bottleneck for light coupling via the apex is its ability to resonantly interact with the incident light, which is only possible for apex radii commensurate with the wavelength. Once light has been fed into the apex, however, the fundamental guided mode of the dielectric tip is excited independently from the apex size. The existence and propagation of the fundamental mode from the apex into the shank are supported experimentally by the observation of periodic ripples close to the apex of a silicon tip irradiated with high-fluence green laser pulses. The periodicity and attenuation of these ripples along the tip axis are in excellent agreement with the theoretical properties of the fundamental guided mode.

A scanning pulse-periodic laser based on heterostructures containing ZnSe with electron beam pumping

Characteristics of a scanning pulsed green laser based on heterostructures containing ZnSe pumped by an electron beam with 200-ns duration and 8-keV energy are studied. If the active element is at room temperature, the scanning frequency is 20 Hz, and the repetition rate is 3 kHz, the average power of laser radiation is 1.6 mW, provided that the pulsed power is 2.7 W.

Thick Single Grain Silicon Formation with Microsecond Green Laser Crystallization

625 nm thick a-Si layer was crystallized by using microsecond pulsed green laser with wavelength of 515 nm. At least 8 μm size grains were formed using location controlled single grain technique at room temperature. Energy density window for crystallization and ablation were compared for pulse durations of 300 ns, 1000 ns and 1200 ns.

Selective desorption of organophosphonates on chemically functionalized titanium by Direct Laser Patterning

Surface functionalization based on organophosphonate molecules and Direct Laser Patterning (DLP) technique both allow to design chemically patterned titanium surfaces devoted to biomaterial engineering. Ultrapolished surfaces of commercially pure titanium were modified with 16-phosphonohexadecanoic acid and octadecylphosphonic acid. The DLP technique with a green pulsed laser was applied to selectively desorb the organophosphonate molecules on the functionalized titanium surfaces. Three regimes of laser ablation were found on the bare titanium surfaces as the ratio between the spot diameter and the interspot distance. Finally, the organophosphonate functionalized titanium surfaces subjected to DLP revealed different wettability domains with minimum impact on the roughness, validated by XPS, AFM and ESEM.

Laser diode and pumped Cr:Yag passively Q-switched yellow-green laser at 543 nm

Efficient and compact yellow green pulsed laser output at 543 nm is generated by frequency doubling of a passively Q-switched end diode-pumped Nd:YVO4 laser at 1086 nm under the condition of sup-pressing the higher gain transition near 1064 nm. With 15 W of diode pump power and the frequency doubling crystal LBO, as high as 1.58 W output power at 543 nm is achieved. The optical to optical conversion efficiency from the corresponding Q-switched fundamental output to the yellow green output is 49%. The peak power of the Q-switched yellow green pulse laser is up to 30 kW with 5 ns pulse duration. The output power stability over 8 hours is better than 2.56% at the maximum output power. To the best of our knowledge, this is the highest watt-level laser at 543 nm generated by frequency doubling of a passively Q-switched end diode pumped Nd:YVO4 laser at 1086 nm. DOI: 10.1134/S0030400X13030296

Atom probe tomography of thermally grown oxide scale on FeCrAl

Thermally grown Al₂O₃ scales formed on a FeCrAl alloy were successfully analyzed using pulsed green laser atom probe tomography. Two types of atom probe tomography specimens, the "thin oxide" type: a thin Al₂O₃ layer (<100 nm) with underlying metal (1 μm), and the "thick oxide" type: only with Al₂O₃ (1 μm), were prepared and analyzed. It was found that the thin oxide type yields poorer mass resolution due to a combined effect of laser absorption and thermal conduction effects. Application of a relatively low laser energy yields a better mass resolution and increased multiple events, however, more accurate quantification results. Although no other oxide phase than Al₂O₃ is expected to form, some iron-oxygen and chromium-oxygen molecular ions were recorded at the Al₂O₃/metal interface due to the large change in evaporation field over this zone.

Airborne laser bathymetry – detecting and recording submerged archaeological sites from the air

A new generation of airborne bathymetric laser scanners utilises short green laser pulses for high resolution hydrographic surveying in very shallow waters. The paper investigates its use for the documentation of submerged archaeological structures, introducing the concept of airborne laser bathymetry and focussing on a number of challenges this novel technology still has to face. Using this method, an archaeological pilot study on the northern Adriatic coast of Croatia has revealed sunken structures of a Roman villa. The results demonstrate the potential of this novel technique to map submerged archaeological structures over large areas in high detail in 3D, for the first time providing the possibility for systematic, large-scale archaeological investigation of this environment. The resulting maps will provide unique means for underwater heritage management.

脉冲绿光激光器的研究

脉冲绿光激光器的研究

脉冲绿光激光器的研究

脉冲绿光激光器的研究

A008 Fundamental Study on Micro-welding of Copper by Green Pulsed YAG Laser

A008 Fundamental Study on Micro-welding of Copper by Green Pulsed YAG Laser

The effects of Pulsed Green Laser Annealing for Carbon NanoWalls (CNWs)

ABSTRACTThe effects of the pulsed green laser annealing at ambient nitrogen for two different heights-CNWs grown on silicon substrate were investigated on the crystallinity and morphology using Raman spectroscopy, SEM, TEM and XPS. For the 1μm height-CNWs, the peak intensity of D-band spectra decreased as the laser energy density increased up to 1.3Jcm-2, ID/IG ratio decreased from 2.5 to 0.7. The crystallinity of CNWs was improved by the laser irradiation. For the 1μm height-CNWs irradiated above 1.5Jcm-2, the height of CNWs decreased gradually as the laser energy density increased, it was clarified that the surfaces of CNWs were vaporized by the laser irradiation. For the 20μm height-CNWs, the peak intensity of D band spectra also decreased until the laser energy density increased up to 0.8Jcm-2, ID/IG ratio decreased from 1.6 to 0.5. From the TEM observation of CNWs irradiated at 0.8 Jcm-2, it was confirmed that the laser irradiation changed CNWs to be highly oriented crystal structure. However above 0.8Jcm-2, the crystallinity was deteriorated due to the vaporization of CNWs as the same as the 1μm height-CNWs. The pulsed green laser annealing is effective to improve the crystallinity of CNWs on optimal laser energy density for both height-CNWs, the higher laser energy densities vaporized the CNWs and changed the morphology and crystallinity of CNWs.

201 W picosecond green laser using a mode-locked fiber laser driven cryogenic Yb:YAG amplifier system

We have generated 201 W of green (514.5 nm) average power from a frequency-doubled picosecond cryogenic Yb:YAG laser system driven by a 50 MHz, 12.4 ps mode-locked Yb fiber laser producing 430 W of average power at 1029 nm, using direct pulse amplification. The fundamental beam produced was near-diffraction-limited (M(2)<1.3). Second-harmonic-generation is achieved using a 20 mm long noncritically phase-matched Lithium triborate (LiB3O5) crystal; conversion efficiencies as high as 58% have been observed. At 100 W of 514.5 nm output power, the average M(2) value was 1.35. To the best of our knowledge, this is the highest average power picosecond green pulsed laser.

Design studies on compact four mirror laser resonator with mode-locked pulsed laser for 5 μm laser wire

A compact prototype four-mirror optical cavity is being constructed at KEK-ATF to measure low-emittance electron beams in the damping ring. Four-mirror-resonators reduce the sensitivity to the misalignment of mirrors in comparison to two mirror-resonators. The aspect ratio is important when constructing a compact resonator with a very small beam waist of less than 5μm. The total cavity length of a four-mirror resonator is matched according to the pulse repetition of mode-locked laser oscillator. Minimum beam waist is obtained in the sagittal plane using an IR pulsed laser. The advantage of such types of compact four-mirror-resonators is the total scanning time for measurement of the beam profile is much shorter in comparison to a CW laser wire system. By using a pulsed green laser that has been converted to the second harmonics from an IR pulsed laser, a minimum beam waist that has half the beam waist when using an IR laser oscillator can be obtained. Therefore, it is possible to obtain the beam waist of less than 5μm (σ value) that is required for effective photon–electron collision. We report on the development and performance studies for such types of compact four-mirror laser wire systems.

Modeling and optimization of pulsed green laser dicing of sapphire using response surface methodology

Laser dicing of single-crystalline sapphire substrate (α-Al2O3) with a pulsed Nd:YAG green (λ=532nm) is investigated. The Box–Behnken Design (BBD) technique based response surface methodology (RSM) is employed to plan the experiment, then empirical models are developed to determine the correlation between responses and input variables, and finally multi-response optimization and quality testing are performed to obtain the optimum operating conditions. In the design of experiment (DOE), processing parameters, such as the pulse laser energy, scanning velocity and scanning times, are considered as the input independent variables, and the groove depth and width as the targeted responses. Results identify the most predominant parameters on the responses, provide insight into the interactions of these parameters, and obtain the optimized operating conditions. The specific combination-pulse laser energy of 150μJ, scanning velocity of 0.55mm/s, scanning times of three, can obtain a deep groove depth of 148μm, narrow groove width of 19μm with good dicing quality.

BiOCl-assisted photodegradation of Rhodamine B under white light and monochromatic green pulsed laser irradiation

BiOCl-assisted photodegradation of Rhodamine B (Rh. B) molecules was investigated by using white light and green pulsed laser as sources of irradiation in the visible region for the first time. The dependences of removal efficiencies on catalyst dosage, incident pulsed laser energy were investigated and discussed. The dissolved oxygen was found to play an important role during the photochemical reaction. In addition the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) levels of Rh. B molecular were calculated using a Gaussian 03 program. These calculations were valuable to identify the possible photo-catalytic excitation process involved in degradation of Rh.B.