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1.
We report the observation of crystallization and simultaneous formation of surface microstructures in hydrogenated amorphous
silicon (a-Si:H) thin films as one step laser processing. Light trapping microstructures of around 300 nm in height were formed
on a-Si:H films of thickness in the range of 1.5 μm to 2 μm deposited on soda lime glass after exposure to femtosecond laser
pulses. Scanning electron microscope (SEM) images show the formation of spikes that are around 1 μm part and their heights
could be controlled by the laser fluences. Atomic force microscope (AFM) images were taken to study the roughness created
on the surface. The mean roughness of the textured surface increases with laser fluence at smaller power densities, and for
power densities beyond 0.5 J/cm2 the film removal deteriorates the texturing. X-ray diffraction results indicate the formation of a nano-crystalline structure
with (111) and (311) crystal orientation after the laser treatment. The observed black color and enhanced optical absorption
in the near infrared region in laser treated films may be due to a combined effect of light trapping in the micro-structured
silicon surface because of multiple total internal reflections, phase change in the film, possible defect sites induced after
laser treatment and formation of SiOx. Demonstration of light trapping microstructures in thin a-Si:H films and simultaneous crystallization could provide new
opportunities for optoelectronic devices.
PACS 42.55.Px; 42.62.Cf; 81.05.Ge 相似文献
2.
We report on the fabrication of hollow optical waveguides in fused silica using femtosecond laser micromachining. We show
that in such hollow waveguides, high-intensity femtosecond laser beams can be guided with low optical loss. Our technique,
which was established earlier for fabrication of optofluidic structures in glass, can ensure a high smoothness at the inner
surfaces of the hollow waveguides and provide the unique capability of fabrication of hollow waveguides with complex geometries
and configurations. A transmission of ∼90% at 633 nm wavelength is obtained for a 62-mm-long hollow waveguide with an inner
diameter of ∼250 μm. In addition, nonlinear propagation of femtosecond laser pulses in the hollow waveguide is demonstrated,
showing that the spectral bandwidth of the femtosecond pulses can be broadened from ∼27.2 to ∼55.7 nm. 相似文献
3.
T. Imahoko K. Takasago T. Sumiyoshi H. Sekita K. Takahashi M. Obara 《Applied physics. B, Lasers and optics》2007,87(4):629-634
We have developed a 6–12 μm mid-infrared (MIR) femtosecond laser source for glyco-protein structure analysis. The MIR femtosecond
laser pulses are generated by a differential frequency generation (DFG) configuration with a combination of Ti:sapphire based
regeneratively amplified femtosecond laser pulses (780 nm, 160 fs, 1 mJ) and a β-BaB2O4 (BBO) based optical parametric amplifier (OPA). The MIR pulse energy exceeds 4.5 μJ, where a glyco-protein molecule has resonant
absorption lines due to the vibrational–rotational transitions. The pulse width is estimated to be less than 1 ps according
to the cross correlation measurement between the two OPA output pulses. Using the MIR femtosecond laser pulses, we demonstrated
photo-dissociation of the sialyl Lewis X (sLeX) proton added ion, which is the first time to the best of our knowledge.
PACS 42.65.Re; 42.62.-b; 42.60.-b; 42.65.-k; 87.50 相似文献
4.
Csaba László Sajti Svea Petersen Ana Menéndez-Manjón Stephan Barcikowski 《Applied Physics A: Materials Science & Processing》2010,101(2):259-264
In-situ functionalization of gold nanoparticles with fluorophore-tagged oligonucleotides is studied by comparing femtosecond
laser ablation in stationary liquid and in biomolecule flow. Femtosecond laser pulses induce significant degradation to sensitive
biomolecules when ablating gold in a stationary solution of oligonucleotides. Contrary, in-situ conjugation of nanoparticles
in biomolecule flow considerably reduces the degree of degradation studied by gel electrophoresis and UV–Vis spectrometry.
Ablating gold with 100 μJ femtosecond laser pulses DNA sequence does not degrade, while the degree of fluorophore tag degradation
was 84% in stationary solution compared to 5% for 1 mL/min liquid flow. It is concluded that femtosecond laser-induced degradation
of biomolecules is triggered by absorption of nanoparticle conjugates suspended in the colloid and not by ablation of the
target. Quenching of nanoparticle size appears from 0.5 μM biomolecule concentration for 0.3 μg/s nanoparticle productivity
indicating the successful surface functionalization. Finally, increasing the liquid flow rate from stationary to 450 mL/min
enhances nanoparticle productivity from 0.2 μg/s to 1.5 μg/s, as increasing liquid flow allows removal of light absorbing
nanoparticles from the ablation zone, avoiding attenuation of subsequent laser photons. 相似文献
5.
A CW seeded femtosecond optical parametric amplifier, a compromise between OPG/OPA and strongly seeded OPA configurations,
has been demonstrated. An independent CW Nd: YAG laser with sub-watt power decreases the pump threshold of the OPA and improves
the stability of the output pulses considerably. Output signal energies as high as 30 μJ with pulse durations less than 250
fs near 1 μm are reported. from this two-stage device. 相似文献
6.
We obtained an array of multicolored femtosecond laser pulses with as many as 17 different colors that are spatially isolated.
The mechanism of generation was proved to be cascaded four-wave mixing and with the following procedure. The output beam from
a femtosecond laser was split into two. One of the two beams was pulse-compressed with a hollow core fiber and the intensity
of the other was reduced. The two beams were synchronized and combined with a small crossing angle in a plate of fused silica
glass plate. The wavelengths of the sidebands are continuously tunable from near-ultraviolet to near-infrared. The pulse duration,
spatial mode, spectrum, and energy stability of the sidebands were studied. As many as fifteen spectral up-shifted pulses
and two spectral downshifted pulses were obtained with spectral bandwidths broader than 1.8 octaves. Properties such as pulse
energy as high as 1 μmJ, 45 fs pulse duration, smaller than 1.1 times of the diffraction limit Gaussian spatial profile, and
better than 2% RMS power stability of the generated sidebands make it can be used in various experiments. The characterization
showed that the sidebands have sufficiently good qualities to enable application to for various multicolor femtosecond laser
experiments, for example, a multicolor pump-probe experiment. 相似文献
7.
J. Siebenmorgen K. Petermann G. Huber K. Rademaker S. Nolte A. Tünnermann 《Applied physics. B, Lasers and optics》2009,97(2):251-255
Single tracks and pairs of tracks were written into undoped and Nd-doped YAG crystals using a commercial femtosecond laser
system delivering pulses with pulse duration of 140 fs and pulse energies up to 10 μJ. The pulses were focused by a 50× microscope
objective below the surface of the crystals. Due to the elasto-optical effect, stress-induced birefringence was observed in
domains surrounding the single tracks and between the pairs of tracks. Waveguiding was demonstrated in certain channels in
these domains. To investigate the underlying guiding mechanism highly selective chemical etching of the modified material
was performed with etching rates up to 5 μm/h. Pumped at 808 nm, laser operation at a wavelength of 1064 nm was achieved.
The maximum output power was 25.5 mW at 261 mW of launched pump power with a slope efficiency of 23%. 相似文献
8.
A possibility of the femtosecond laser system with a pulse duration of about 300 fs and an energy of 150 nJ in a range of
1.6 μm based on side-coupled fibers one of which is doped with erbium and is pumped through cladding is demonstrated. The
parameters of a ring master oscillator and an amplifier that make it possible to generate femtosecond pulses with a peak power
of up to 450 kW are presented. 相似文献
9.
C. Zhou Y. Cai L. Ren P. Li S. Cao L. Chen M. Zhang Z. Zhang 《Applied physics. B, Lasers and optics》2009,97(2):445-449
We demonstrated a self-starting passively synchronized Er- and Yb-fiber laser system. Synchronization was implemented by the
master-slave configuration where partial output power of the Er-fiber laser was injected into the Yb-fiber laser via a 2-m-long
single-mode fiber. The output pulses both were in femtosecond range, and the cavity mismatch tolerance was 160 μm, corresponding
to 1267 Hz in frequency domain. The RMS (root mean square) timing jitter between these two lasers was calculated as 14.7 fs
(5-kHz bandwidth) in one second. 相似文献
10.
The generation of programmable complex femtosecond pulses in the mid infrared (3–10 μm) with high precision is reported. Designed
pulse shapes in the near infrared (1–1.6 μm) are transferred to the mid infrared via difference-frequency mixing with a second
infrared pulse spectrally narrowed in a zero-dispersion compressor. In particular, pulse sequences with variable relative
phases have been obtained. The control of the pulse properties is achieved purely electronically, allowing for implementation
into a feedback loop.
Received: 12 December 2003 / Published online: 3 April 2003
RID="*"
ID="*"Corresponding author. Fax: +49-89/32905-200, E-mail: mcm@mpq.mpg.de 相似文献
11.
D.A. Akimov A.A. Ivanov M.V. Alfimov S.N. Bagayev T.A. Birks W.J. Wadsworth P.St.J. Russell A.B. Fedotov V.S. Pivtsov A.A. Podshivalov A.M. Zheltikov 《Applied physics. B, Lasers and optics》2002,74(4-5):307-311
Spectral broadening of femtosecond Cr:forsterite laser pulses is enhanced due to the use of tapered fibers. Supercontinuum
generation with unamplified subnanojoule femtosecond Cr:forsterite laser pulses is observed for the first time. With 40-fs
0.6-nJ pulses of 1.25-μm Cr:forsterite laser radiation coupled into a tapered fiber having a taper waist diameter of about
2 μm and a taper waist length of 90 mm, we observed the spectra spanning more than two octaves at the output of the fiber
in the regime of anomalous group-velocity dispersion. This result opens the way for the creation of compact femtosecond Cr:forsterite
laser plus tapered fiber systems for optical metrology and biomedical applications.
Received: 23 October 2001 / Accepted: 16 January 2002 / Published online: 14 March 2002 相似文献
12.
W. J. Mandeville M. K. Shaffer Yalin Lu D. O’Keefe R. J. Knize 《Applied Physics A: Materials Science & Processing》2011,104(2):755-758
We produce microstructured silicon using frequency doubled, nanosecond Nd:YAG pulses in SF6 gas. The micro-penitentes formed are up to 20 μm tall with a sulfur concentration of 0.5% near the surface. The infrared
absorption is increased to near unity and extends well below the original bandgap far into the infrared. These data are similar
to results reported by others using more complicated and less economical femtosecond titanium sapphire and picosecond and
nanosecond excimer lasers. 相似文献
13.
We developed a high-power oscillator–regenerative amplifier femtosecond laser system. Based on chromium-doped forsterite.
The system is operating near 1.25 μm at a 5–10 kHz repetition rate. Chirped-pulse amplification produced 0.86 W (0.75 W) of
average power, or 465 mW (400 mW) after compression at 5 kHz (10 kHz). Nearly bandwidth-limited pulses of duration 135 fs
(shortest) and 150 fs (typical) are available with an energy of 93 μJ and 40 μJ at 5 and 10 kHz, respectively.
Received: 7 June 2002 / Published online: 15 November 2002
RID="*"
ID="*"Corresponding author. Fax: +49-30/63921289, E-mail: petrov@mbi-berlin.de 相似文献
14.
L. Daniault D. A. Gaponov M. Hanna S. Février P. Roy F. Druon P. Georges M. E. Likhachev M. Y. Salganskii M. V. Yashkov 《Applied physics. B, Lasers and optics》2011,103(3):615-621
We report on high power amplification of femtosecond pulses in 40-μm core diameter Yb-doped photonic bandgap Bragg fibers.
The robustness to bending and transverse spatial behavior of these fibers is analyzed through simulations. The fibers are
used in both stages of a moderately stretched (150 ps) femtosecond chirped pulsed amplification (CPA) system. A compressed
average power of 6.3 W is obtained using a low-index polymer-coated Bragg fiber with excellent beam quality and high efficiency,
in agreement with numerical simulations. The use of an air-clad Bragg fiber allows us to scale the output power to 47 W at
a repetition rate of 35 MHz. This experiment demonstrates the great potential of Bragg fibers to increase the mode area and
the power of practical bending-tolerant femtosecond fiber systems. 相似文献
15.
M. Hoffmann Y. Barbarin D. J. H. C. Maas M. Golling I. L. Krestnikov S. S. Mikhrin A. R. Kovsh T. Südmeyer U. Keller 《Applied physics. B, Lasers and optics》2008,93(4):733-736
We report the first successful modelocking of a vertical external cavity surface emitting laser (VECSEL) with a quantum dot
(QD) gain region. The VECSEL has a total of 35 QD-layers with an emission wavelength of about 1060 nm. In SESAM modelocked
operation, we obtain an average output power of 27.4 mW with 18-ps pulses at a repetition rate of 2.57 GHz. This QD-VECSEL
is used as-grown on a 450 μm thick substrate, which limits the average output power. 相似文献
16.
We report a direct observation of the temperature field on a steel specimen during ablation by multiple femtosecond laser pulses using an infrared thermography technique. From the experimental results and simulation study of the temperature field, we quantified the deposited thermal power into the specimen during the ablation process. We found that more than two thirds of the incident laser power was deposited in the steel specimen when ablated by multiple femtosecond laser pulses. This result provides further understanding of the heating effect in materials processing by ultrashort laser pulses. 相似文献
17.
C. M. Zhang J. L. Wang L. W. Song C. Li Y. S. Huang Y. X. Leng R. X. Li Z. Z. Xu 《Laser Physics》2010,20(4):727-732
High-conversion-efficiency and tunable self-phase-stabilized infrared laser pulses have been generated from a two-stage optical
parametric amplifier. With a 1 kHz repetition rate 800 nm pump source, the output idler pulses are tunable from 1.2 to 2.4
μm, and the maximum output average power of the idler pulses is >2 W with the total 7.4 W pump power, and the maximum parametric
conversion efficiency in the final optical parametric amplifier is near 60%. Due to the differential frequency process, the
output idler pulses is self-phase-stabilized, the phase fluctuation can reach 0.374 rad (rms). 相似文献
18.
L. Englert M. Wollenhaupt L. Haag C. Sarpe-Tudoran B. Rethfeld T. Baumert 《Applied Physics A: Materials Science & Processing》2008,92(4):749-753
Laser material processing of dielectrics with temporally asymmetric femtosecond laser pulses of identical fluence, spectrum,
and statistical pulse duration is investigated experimentally. To that end single shot structures at the surface of fused
silica as a function of fluence and pulse shape are analyzed with the help of scanning electron microscopy. Structures for
the bandwidth limited pulses show the known expansion in structure size with increasing laser fluence approaching the diffraction
limit, which is 1.4 μm for the 0.5NA microscope objective used. In contrast, structures from the asymmetric pulses are remarkably
stable with respect to variations in laser fluence and stay below 300 nm despite doubling the fluence. Different thresholds
for surface material modification with respect to an asymmetric pulse and its time reversed counterpart are attributed to
control of different ionization processes. 相似文献
19.
The hard X-ray yield generated with femtosecond laser pulses is studied for differently chirped irradiating laser pulses.
The radiation of a Ti:sapphire CPA laser system (29 fs, 750 μJ, 1 kHz) is focused onto an iron containing solid state target
producing incoherent hard X-ray radiation, Bremsstrahlung as well as target-specific Kα and Kβ lines. The hard X-ray yield has been optimized by introducing negative and positive group delay dispersion (GDD) and third
order dispersion (TOD) to the femtosecond laser pulse. The Kα yield could be enhanced by a factor of 1.7 and reached 1.9×108 Fe Kα photons/s in 4π with the laser pulse positively chirped, and 1.5×108 Fe Kα photons/s with the pulse negatively chirped. When the pulse energy is lowered to about 400 μJ the yield maximum at negative
chirp vanishes and only the maximum at positive chirp remains. We explain this behavior with an increased electron temperature
caused by the induced GDD and TOD in the pulse.
PACS 42.65.Re; 52.38.Ph; 52.50.Jm 相似文献
20.
We studied the absorption spectrum of intact human tooth enamel and dentine in the range of 0.26–10 μm. We present the infrared
absorption spectra of destruction products of human tooth enamel and dentine by submillisecond laser pulses on a crystal of
yttrium-scandium-gallium garnet, activated by chrome and erbium ions with a wavelength of 2.79 μm. We discuss the effect of
water spraying on the mechanism of laser ablation and the infrared absorption spectra. We report for the first time transformations
observed in the absorption spectra of human tooth enamel in the wavelength range of 2.5–3.5 μm under its heating to +700°C. 相似文献