共查询到20条相似文献,搜索用时 23 毫秒
1.
R. A. Ganeev M. Baba A. I. Ryasnyansky M. Suzuki H. Kuroda 《Applied physics. B, Lasers and optics》2005,80(4-5):595-601
We investigated the optical, structural, and nonlinear optical properties of GaAs nanoparticles prepared by laser ablation in various liquids at the wavelengths of 795 nm and 1,054 nm. The slow-thermal-effect-induced self-defocusing processes were dominating both in the cases of high pulse repetition rate and nanosecond pulses. The two-photon absorption was observed in these colloidal solutions in the case of low pulse repetition rate of picosecond and femtosecond radiation. The nonlinear susceptibility of GaAs nanoparticles ablated in water was measured to be 2× 10–9 esu. 相似文献
2.
W. Kautek S. Mitterer J. Krüger W. Husinsky G. Grabner 《Applied Physics A: Materials Science & Processing》1994,58(5):513-518
A femtosecond pulse laser in the visible spectral region shows promise as a potentially new powerful corneal sculpting tool. It combines the clinical and technical advantages of visible wavelengths with the high ablation quality observed with nanosecond-pulse excimer lasers at 193 nm. A femtosecond and a nanosecond dye laser with pulse durations of 300 fs and 7 ns, and centre wavelengths at 615 nm and 600 nm, respectively, both focused to an area of the order of 10–5 cm2, have been applied to human corneal ablation. Nanosecond laser pulses caused substantial tissue disruption within a 30–100 m range from the excision edge at all fluences above the ablation threshold of F
th60 J cm–2 (I
th9 GW cm–2). Completely different excisions are produced by the femtosecond-pulse laser: high quality ablations of the Bowman membrane and the stroma tissue characterised by damage zones of less than 0.5 m were observed at all fluences above ablation threshold of F
th1 J cm–2 or I
th3 TW cm–2 (3×1012 W cm–2). The transparent cornea material can be forced to absorb ultrashort pulses of extremely high intensity. The fs laser generates its own absorption by a multiphoton absorption process. 相似文献
3.
The dependence of the ablation rate of aluminium on the fluence of nanosecond laser pulses with wavelengths of 532 nm and
respectively 1064 nm is investigated in atmospheric air. The fluence of the pulses is varied by changing the diameter of the
irradiated area at the target surface, and the wavelength is varied by using the fundamental and the second harmonic of a
Q-switched Nd-YAG laser system. The results indicate an approximately logarithmic increase of the ablation rate with the fluence
for ablation rates smaller than ∼6 μm/pulse at 532 nm, and 0.3 μm/pulse at 1064 nm wavelength. The significantly smaller ablation rate at 1064 nm is due to the small optical absorptivity,
the strong oxidation of the aluminium target, and to the strong attenuation of the pulses into the plasma plume at this wavelength.
A jump of the ablation rate is observed at the fluence threshold value, which is ∼50 J/cm2 for the second harmonic, and ∼15 J/cm2 for the fundamental pulses. Further increasing the fluence leads to a steep increase of the ablation rate at both wavelengths,
the increase of the ablation rate being approximately exponential in the case of visible pulses. The jump of the ablation
rate at the threshold fluence value is due to the transition from a normal vaporization regime to a phase explosion regime,
and to the change of the dimensionality of the hydrodynamics of the plasma-plume.
相似文献
4.
T. I. Karu P. G. Kryukov V. S. Letokhov Yu. A. Matveetz V. A. Semchishen 《Applied Physics A: Materials Science & Processing》1981,24(3):245-247
The action of powerful pulsed picosecond radiation from a Nd: YAG laser (λ=530 nm, pulse energy: 0.01 J, intensity: 2GW/cm2) and an argon laser (λ=515 nm, power: 50 mW) on protoporphyrin-IX dimethylether in three solvents (trichlormethane, carbon
tetrachloride, dioxane) has been studied. Under continuous irradiation the quantum yield and resulting products do not differ
materially from the ones produced under mercury lamp irradiation. When irradiation is performed by powerful laser pulses of
picosecond duration the quantum yield of photodecomposition of protoporphyrin-IX dimethylether inereases substantially: by
10 in dioxane, by 4 in carbon tetrachloride and by 100 in trichlormethane. It is assumed that a quite different mechanism
of multistep excitation is responsible for photodecomposition under powerful picosecond pulses. 相似文献
5.
The selective ablation of thin (∼100 nm) SiO2 layers from silicon wafers has been investigated by applying ultra-short laser pulses at a wavelength of 800 nm with pulse
durations in the range from 50 to 2000 fs. We found a strong, monotonic decrease of the laser fluence needed for complete
ablation of the dielectric layer with decreasing pulse duration. The threshold fluence for 100% ablation probability decreased
from 750 mJ/cm2 at 2 ps to 480 mJ/cm2 at 50 fs. Significant corruption of the opened Si surface has been observed above ∼1200 mJ/cm2, independent of pulse duration. By a detailed analysis of the experimental series the values for melting and breaking thresholds
are obtained; the physical mechanisms responsible for the significant dependence on the laser pulse duration are discussed. 相似文献
6.
A long train of actively mode-locked pulses is obtained from a negative feedback controlled Nd:YAG laser. The 70s pulse train contains up to 0.1 J energy and the duration of the picosecond pulses is 120 ps. The laser is operated at a repetition rate of 20 Hz. ActiveQ-control of the cavity generates a short pulse train of duration 50 to 70 ns. An excellent peak-to-background intensity ratio of the correlation function for the picosecond pulses in the train of 5×103 is reported. 相似文献
7.
N. G. Semaltianos W. Perrie P. French M. Sharp G. Dearden S. Logothetidis K. G. Watkins 《Applied Physics A: Materials Science & Processing》2009,94(4):999-1009
Femtosecond laser (180 fs, 775 nm, 1 kHz) ablation characteristics of the nickel-based superalloy C263 are investigated. The
single pulse ablation threshold is measured to be 0.26±0.03 J/cm2 and the incubation parameter ξ=0.72±0.03 by also measuring the dependence of ablation threshold on the number of laser pulses.
The ablation rate exhibits two logarithmic dependencies on fluence corresponding to ablation determined by the optical penetration
depth at fluences below ∼5 J/cm2 (for single pulse) and by the electron thermal diffusion length above that fluence. The central surface morphology of ablated
craters (dimples) with laser fluence and number of laser pulses shows the development of several kinds of periodic structures
(ripples) with different periodicities as well as the formation of resolidified material and holes at the centre of the ablated
crater at high fluences. The debris produced during ablation consists of crystalline C263 oxidized nanoparticles with diameters
of ∼2–20 nm (for F=9.6 J/cm2). The mechanisms involved in femtosecond laser microprocessing of the superalloy C263 as well as in the synthesis of C263
nanoparticles are elucidated and discussed in terms of the properties of the material. 相似文献
8.
Ultra-short pulsed laser ablation and micromachining of n-type, 4H-SiC wafer was performed using a 1552 nm wavelength, 2 ps pulse, 5 μJ pulse energy erbium-doped fiber laser with an objective of rapid etching of diaphragms for pressure sensors. Ablation rate, studied as a function of energy fluence, reached a maximum of 20 nm per pulse at 10 mJ/cm2, which is much higher than that achievable by the femtosecond laser for the equivalent energy fluence. Ablation threshold was determined as 2 mJ/cm2. Scanning electron microscope images supported the Coulomb explosion (CE) mechanism by revealing very fine particulates, smooth surfaces and absence of thermal effects including melt layer formation. It is hypothesized that defect-activated absorption and multiphoton absorption mechanisms gave rise to a charge density in the surface layers required for CE and enabled material expulsion in the form of nanoparticles. Trenches and holes micromachined by the picosecond laser exhibited clean and smooth edges and non-thermal ablation mode for pulse repetition rates less than 250 kHz. However carbonaceous material and recast layer were noted in the machined region when the pulse repetition rate was increased 500 kHz that could be attributed to the interaction between air plasma and micro/nanoparticles. A comparison with femtosecond pulsed lasers shows the promise that picosecond lasers are more efficient and cost effective tools for creating sensor diaphragms and via holes in 4H-SiC. 相似文献
9.
E. D'Anna S. Luby A. Luches E. Majkova M. Martino 《Applied Physics A: Materials Science & Processing》1993,56(5):429-436
Interdiffusion phenomena, thermal damage and ablation of W/Si and Si/W bilayers and multilayers under XeCl-excimer laser (=308 nm) irradiation at fluences of 0.15, 0.3 and 0.6 J/cm2 were studied. Samples were prepared by UHV e-beam evaporation onto oxidized Si. The thickness of W and Si layers and the total thickness of the structures were 1–20 nm and 40–100 nm, respectively. 1 to 300 laser pulses were directed to the same irradiation site. At 0.6 J/cm2 the samples were damaged even by a single laser pulse. At 0.3 J/cm2 WSi2 silicide formation, surface roughening and ablation were observed. The threshold for significant changes depends on the number of pulses: it was between 3–10 pulses and 10–30 pulses for bilayers with W and Si surfaces, respectively, and more than 100 pulses for multilayers with the same total thickness of tungsten. At 0.15 J/cm2 the periodicity of the multilayers was preserved. Temperature profiles in layered structures were obtained by numerical simulations. The observed differences of the resistance of various bilayers and multilayers against UV irradiation are discussed. 相似文献
10.
N.E. Karatzas 《Optics Communications》2006,267(2):498-504
Calculations are presented for the first four (odd and even) harmonics of an 800 nm laser from a gold surface, with pulse widths ranging from 100 down to 14 fs. For peak laser intensities above 1 GW/cm2 the harmonics are enhanced because of a partial depletion of the initial electron states. At 1011 W/cm2 of peak laser intensity the calculated conversion efficiency for 2nd-harmonic generation is 3 × 10−9, while for the 5th-harmonic it is 10−10. The generated harmonic pulses are broadened and delayed relative to the laser pulse because of the finite relaxation times of the excited electronic states. The finite electron relaxation times cause also the broadening of the autocorrelations of the laser pulses obtained from surface harmonic generation by two time-delayed identical pulses. Comparison with recent experimental results shows that the response time of an autocorrelator using nonlinear optical processes in a gold surface is shorter than the electron relaxation times. This seems to indicate that for laser pulses shorter than ∼30 fs, the fast nonresonant channel for multiphoton excitation via continuum-continuum transitions in metals becomes important as the resonant channel becomes slow (relative to the laser pulse) and less efficient. 相似文献
11.
Alex Spiro Mary Lowe Guerman Pasmanik 《Applied Physics A: Materials Science & Processing》2012,107(4):801-808
Experimental results on picosecond laser processing of aluminum, nickel, stainless steel, molybdenum, and tungsten are described. Hole drilling is employed for comparative analysis of processing rates in an air environment. Drilling rates are measured over a wide range of laser fluences (0.05–20?J/cm2). Experiments with picosecond pulses at 355?nm are carried out for all five metals and in addition at 532?nm, and 1064?nm for nickel. A comparison of drilling rate with 6-ps and 6-ns pulses at 355?nm is performed. The dependence of drilling rate on laser fluence measured with picosecond pulses demonstrates two logarithmic regimes for all five metals. To determine the transition from one regime to another, a critical fluence is measured and correlated with the thermal properties of the metals. The logarithmic regime at high-fluence range with UV picosecond pulses is reported for the first time. The energy efficiency of material removal for the different regimes is evaluated. The results demonstrate that UV picosecond pulses can provide comparable quality and higher processing rate compared with literature data on ablation with near-IR femtosecond lasers. A significant contribution of two-photon absorption to the ablation process is suggested to explain high processing rate with powerful UV picosecond pulses. 相似文献
12.
A synchronously mode-locked, cavity-dumped picosecond dye laser is described. The structure and intensity of the picosecond
pulses measured under different conditions are reported. It was found that the structure of the pulses from the synchronously
pumped dye laser depends critically on the length of the Ar+ laser pulses. At the shortest Ar+ laser pulses of about 70 ps the dye pulses are as short as 1.1 ps. With Ar+ laser pulses of 200 ps the dye laser pulses contains a broad satellite pulse which contains a large fraction of the total
intensity. When a cavity dumper is added to the system one gets dye laser pulses 15–20 ps long with a substructure, which
indicates incomplete mode-locking. Well mode-locked 1.5–2.0 ps pulses were obtained in the red part of the dye laser action
spectrum, i.e. 620–650 nm for R6G, 595–608 nm for R 110 and 657–662 nm for RB, respectively. Addition of mode-locking dyes
also improved the pulse quality at some wavelengths. 相似文献
13.
A. Matusevich A. Tolstik M. Kisteneva S. Shandarov V. Matusevich A. Kiessling R. Kowarschik 《Applied physics. B, Lasers and optics》2008,92(2):219-224
A photorefractive Bi12TiO20 (BTO) crystal is exposed with high intensity pulsed-laser beams 532 nm (the average intensity of the laser was 110 mW/cm2, the average intensity per pulse was 2 MW/cm2), and the photo-induced dynamics of the absorption between 480 and 900 nm are studied and explained by two long-lived energy
levels in the forbidden band. The relaxation times of the long-lived energy levels are experimentally found to be 104 and 105 s. The hysteresis character of the absorption coefficient is discussed.
PACS 42.70.Mp; 42.70.Gi 相似文献
14.
W. KLodzimierz Nakwaski 《Optical and Quantum Electronics》1979,11(4):319-327
The analysis of the heat spreading in the single-heterostructure GaAs-Ga1-x Al
x
As laser diode supplied with short current pulses (in the case, however, when the adiabatic approximation is no longer valid) at room temperature is presented in this paper. Relations are derived, describing the time-dependent temperature rise within the volume of the laser diode. The calculations are carried out for a typical SH laser diode. It turns out that in the duration of the short current pulses (t
I=200 ns,j=1.5 × 104A cm–2) the increase in junction temperature of the typical SH laser diode amounts to about 6.1 K. This increase leads to an increase of about 9% in the threshold current, to a decrease of about 18% in the laser radiation intensity, and to a shift of the spontaneous radiation band and of the stimulated radiation modes of about 1.9 nm and 0.22 nm, respectively, during each current pulse. 相似文献
15.
Sumei Wang Qinan Li Qiulin Zhang Jie Xing Baohua Feng Shiwen Zhang 《Optics Communications》2007,277(1):130-133
Simultaneous self-Q-switched and mode-locked have been demonstrated in a diode-pumped Nd,Cr:YAG laser. For the first time as we know, almost 100% modulation depth has been achieved at an intracavity intensity of 5.6 × 105 W/cm2. The maximum average output power of 6.52 W corresponding to a slope efficiency of 30% is obtained at 1064 nm. The laser produces high-quality pulses in a TEM00-mode at the pump power of 16.5 W. The pulse duration of the mode-locked pulses is about 600 ps with 136 MHz repetition rate. 相似文献
16.
E. Yu. Loktionov A. V. Ovchinnikov Yu. Yu. Protasov D. S. Sitnikov 《Journal of Applied Spectroscopy》2010,77(4):561-568
We present the results of an experimental study of the ablation energy thresholds and ablated mass for a number of refractory
metals (Ti, Zr, Nb, Mo) by femtosecond (τ
0.5 = 45–70 fs) exposed to laser pulses in the ultraviolet — near infrared range (λ = 266, 400, 800 nm) under atmospheric conditions and under vacuum (p ~ 10–2 Pa). We have analyzed the ablation efficiency (mass yield per unit energy of the acting coherent radiation) and ablation
energy thresholds vs. the laser pulse duration and photon energy. 相似文献
17.
K.L. Ishikawa 《Applied physics. B, Lasers and optics》2004,78(7-8):855-858
We simulate the response of He+ exposed simultaneously to fundamental and 27th harmonic pulses from an intense Ti:sapphire laser. High-order harmonic emission from He+ is enhanced by 17 orders of magnitude compared with the case of the fundamental pulse alone. Moreover, while an individual 10 fs laser with a fundamental wavelength of 800 nm and a peak intensity of 3×1014 W/cm2, or its 27th harmonic pulse with a peak intensity of 1013 W/cm2, ionizes no more than 5×10-6 of He+, their combined pulses lead to a surprisingly high He2+ yield of 17%. The underlying mechanism is either harmonic generation from a coherent superposition of states or two-color frequency mixing, depending on the laser wavelength. PACS 32.80.Rm; 42.50.Hz; 42.65.Ky 相似文献
18.
J. P. Fischer J. Dams M. H. Götz E. Kerker F. H. Loesel C. J. Messer M. H. Niemz N. Suhm J. F. Bille 《Applied physics. B, Lasers and optics》1994,58(6):493-499
Plasma-mediated ablations of brain tissue have been performed using picosecond laser pulses obtained from a Nd:YLF oscillator/regenerative amplifier system. The laser pulses had a pulse duration of 35 ps at a wavelength of 1.053 µm. The pulse energy varied from 90 µJ to 550 µJ at a repetition rate of 400 Hz. The energy density at the ablation threshold was measured to be 20 J/cm2. Comparisons have been made to 19 ps laser pulses at 1.68 µm and 2.92 µm from an OPG/OPA system and to microsecond pulse trains at 2.94 µm from a free running Er:YAG laser. Light microscopy and scanning electron microscopy were performed to judge the depth and the quality of the ablated cavities. No thermal damage was induced by either of the picosecond laser systems. The Er:YAG laser, on the other hand, showed 20 µm wide lateral damage zones due to the longer pulse durations and the higher pulse energies. 相似文献
19.
Shifeng Du Dongxiang Zhang Baohua Feng Jing-Yuan Zhang Jing-Cun Zang 《Optics Communications》2009,282(14):2960-12186
We report the generation of high-peak power multi-wavelength picosecond laser pulses using optical parametric amplification (OPA) in BBO seeded with pulses generated in a 5-mm length BaWO4 crystal by stimulated Raman scattering of 18-ps laser pulses at 532 nm. The maximum output energy of the amplified first-Stokes component at 559.7 nm was about 1.76 mJ. The corresponding maximum peak power, pulse duration and spectral line width were measured to be 117.3 MW, 15 ps and 18.0 cm−1, respectively. The multi-wavelength picosecond laser pulses were in the visible and near infrared ranges. Using this Raman-seeded OPA technique, the beam quality of the stimulated Raman scattering pulses can be improved. 相似文献
20.
S. Banerjee G. Ravindra Kumar L.C. Tribedi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,10(2):295-300
We present studies of X-ray emission from aluminium under picosecond and femtosecond irradiation in the intensity range 1012-1015 W cm-2. We use a new and simple method to measure spectrally resolved absolute X-ray yields. It is shown that the X-ray yields can be obtained for arbitrary levels of X-ray flux. We
present details of the variation of the absolute yields as a function of wavelength, intensity, polarization and pulse duration
of the incident laser radiation. Electron temperatures in the keV range are observed at 1015 W cm-2 with femtosecond laser pulses.
Received 12 August 1999 and Received in final form 29 November 1999 相似文献