共查询到20条相似文献,搜索用时 234 毫秒
1.
Yudi Rosandi Herbert M. Urbassek 《Applied Physics A: Materials Science & Processing》2010,101(3):509-515
The optical properties of blue-violet InGaN light-emitting diodes under normal and reversed polarizations are numerically
studied. The best light-emitting performance under normal and reversed polarization is obtained in a single quantum-well structure
and double quantum-well structure, respectively. The key factors responsible for these phenomena are presumably the carrier
concentration distribution and the amount of carriers in quantum wells. The turn-on voltage of light-emitting diodes under
reversed polarization is lower than that of light-emitting diodes under normal polarization, due mainly to lower potential
heights for electrons and holes in the active region. 相似文献
2.
E. Takahashi S. Kato Y. Matsumoto I. Okuda 《Applied physics. B, Lasers and optics》2010,98(2-3):501-505
External-laser-induced preionization of excimer lasers was investigated. A discharge XeF laser was preionized by two different UV lasers [a KrF laser (λ=249 nm) and an ArF laser (λ=193 nm)], and the improvements in performance of the XeF laser were compared. The XeF laser beam profiles were measured by an intensified CCD (ICCD) camera with temporal resolution of 10 ns. Striated XeF laser profiles were obtained with 249 nm laser preionization, whereas there was no striation in the profiles for 193 nm laser preionization. These striations originated from discharge in the XeF laser induced by laser preionization. The influence of excited rare-gas atoms on the discharge instability was examined. 相似文献
3.
C. Li X. Shi J. Si F. Chen T. Chen Y. Zhang X. Hou 《Applied physics. B, Lasers and optics》2010,98(2-3):377-381
Photoinduced multiple microchannels in the interior of silicon produced by an 800-nm femtosecond laser were observed. The multiple microchannels were aligned spontaneously with a period along the propagation direction of the laser beam, which could be attributed to the interface spherical aberration induced due to refractive-index mismatch. We also observed that the depth of the photoinduced microchannels increased with the increase of the laser power. The power dependence of the depth of photoinduced microchannels in silicon was different from that in transparent materials, which probably arose from the competition between self-focusing due to the nonlinear Kerr effect and self-defocusing related to the thermal accumulation in the process of laser irradiation. 相似文献
4.
E. Schulz T. Binhammer D. S. Steingrube S. Rausch M. Kovacev U. Morgner 《Applied physics. B, Lasers and optics》2009,95(2):269-272
Sub-10-fs-pulses are generated by self-compression in a noble gas filament. Using input pulses from a Ti:sapphire amplifier
system with an energy of about 1.5 mJ at a repetition rate of 3 kHz and a pulse duration of 30 fs self-compressed sub-10-fs
pulses with energies of about 0.3 mJ have been generated. These pulses are characterized with spectral phase interferometry
for direct electrical-field reconstruction (SPIDER). Depending on the laser parameters, we observe a significant change in
the chirp of the white-light. The spectral distribution of the outcoming beam profile is measured to distinguish the white-light
core from the surrounding halo. 相似文献
5.
N. G. C. Astrath F. B. G. Astrath J. Shen J. Zhou C. E. Gu L. C. Malacarne P. R. B. Pedreira A. C. Bento M. L. Baesso 《Applied physics. B, Lasers and optics》2009,94(3):473-481
A complete theoretical model is presented for the thermal mirror technique under top-hat laser excitation. Considering the
attenuation of the top-hat excitation laser intensity along the thickness of a sample due to its optical absorption coefficient,
we calculate the laser-induced temperature and surface deformation profiles. A simplified theoretical model for a high absorption
sample is also developed. The center intensity of a probe beam reflected from the thermal mirror at a detector plane is derived.
Numerical simulation shows that the thermal mirror under the top-hat laser excitation is as sensitive as that under Gaussian
laser excitation. With top-hat laser excitation, the experimental results of thermo-physical properties of opaque samples
are found to be well consistent with literature values, validating the theory. 相似文献
6.
A parameter for evaluating the sensitivity of quantum vibrational energy to anharmonicity in a diatomic gasdynamic laser is defined and calculated by considering the corresponding diatomic molecules as quantum anharmonic oscillators under an interatomic Morse potential. The variation of the above parameter in terms of the vibrational states and in terms of an involved anharmonic coefficient is discussed. In particular, the parameter in question at the classical limit is examined. Both weak and strong anharmonicities are discussed. 相似文献
7.
We describe the application of a long-wavelength vertical-cavity surface-emitting laser (VCSEL) with extended tuning range
to the detection of benzene vapor at atmospheric pressure. A benzene absorption feature centered at 1684.24 nm was accessed
by reducing the heat sink temperature of a VCSEL designed for room-temperature operation to −55°C. This allowed us to increase
the injection current and thus to extend a single-scan tuning interval up to 46.4 cm−1 or 13.2 nm around a central wavelength of 1687.4 nm. Five absorption lines of methane in the 5903–5950 cm−1 range could be acquired within single laser scans at a repetition rate of 500 Hz. A benzene absorption feature between 5926
and 5948 cm−1 was recorded for concentration measurements at atmospheric pressure using a single-pass 1.2 m absorption cell. A 50 ppmv
mixture of CH4 in N2 was introduced into the cell along with benzene vapor to calibrate benzene concentration measurements. Benzene mixing ratios
down to ∼90 ppmv were measured using a direct absorption technique. The minimum detectable absorbance and detection limit
of benzene were estimated to be ∼10−4 and 30 ppmv, respectively. Using the wavelength modulation technique, we measured a second harmonic sensor response to benzene
vapor absorption in air at atmospheric pressure as a function of modulation index. We conclude that a low-temperature monolithic
VCSEL operating near 1684 nm can be employed in compact benzene sensors with a detection limit in the sub-ppm range. 相似文献
8.
T. Ajtai á. Filep A. Varga G. Motika Z. Bozóki G. Szabó 《Applied physics. B, Lasers and optics》2010,101(1-2):403-409
A novel type of system based on a frequency-quadrupled Nd:YAG laser light source at 266 nm and a dual-cell photoacoustic detection unit was developed, and its applicability for ozone-concentration measurement with a minimum detectable ozone concentration of about 100 pptV was demonstrated. The instrument was calibrated against an ozone generator, and it was installed at a regional environmental monitoring station to be operated in parallel with a commercial UV-absorption photometry based ozone-monitoring instrument. While good agreement between the readings of the two systems was found, the photoacoustic system outperformed its optical absorption based counterpart as far as minimum detectable concentration and measurement accuracy is concerned. 相似文献
9.
S. Aggoune F. Vidal E. H. Amara 《Applied Physics A: Materials Science & Processing》2010,101(1):167-171
The interaction between a laser-produced aluminum plasma and the ambient air, at a pressure of 173.3 Pa, is studied at the
plasma thermalization stage. A two-dimensional approach is developed to solve the Navier–Stokes equations, where a finite
volume discretization allows for obtaining a numerical solution. The simulation runs over a time representing 10 μs of plasma
expansion. It is shown that the shock and drag models are good approximations for the two successive regimes after the initial
strong expansion stage, and the calculation makes evident the plume sharpening on the axial direction before its confinement
by the ambient gas, which is in good agreement with the experimental observation. 相似文献
10.
Ming-Chun Tien Aaron T. Ohta Kyoungsik Yu Steven L. Neale Ming C. Wu 《Applied Physics A: Materials Science & Processing》2009,95(4):967-972
Heterogeneous integration of InGaAsP microdisk lasers on a silicon platform is demonstrated experimentally using an optofluidic
assembly technique. The 200-nm-thick, 5- and 10-μm-diameter microdisk lasers are fabricated on InP and then released from
the substrates. They are reassembled on a silicon platform using lateral-field optoelectronic tweezers (LOET). The assembled
laser with 5-μm diameter exhibits a threshold pump power of 340 μW at room temperature under pulse condition. The heterogeneously-integrated
InGaAsP-on-Si microdisk laser could provide the much needed optical source for CMOS-based silicon photonics. The small footprint
and low power consumption make them attractive for optical interconnect applications. The optofluidic assembly technique enables
efficient use of the III–V epitaxial materials in silicon photonic integrated circuits. 相似文献
11.
F. Amrani A. Haboucha M. Salhi H. Leblond A. Komarov F. Sanchez 《Applied physics. B, Lasers and optics》2010,99(1-2):107-114
We investigate experimentally ordered and disordered pattern formation of solitons in a double-clad fiber laser. We point out an analogy between the different states of matter and the states of a set of dissipative solitons. In particular, we have identified a gas, a supersonic gas flow, a liquid, a polycrystal and a crystal of solitons. The different states are obtained only by adjustment of the intracavity phase plates. 相似文献
12.
J. Cheng W. Perrie M. Sharp S. P. Edwardson N. G. Semaltianos G. Dearden K. G. Watkins 《Applied Physics A: Materials Science & Processing》2009,95(3):739-746
Picosecond laser single pulse ablation of Au, Al and Ti alloy (Ti6Al4V) was experimentally investigated with a laser pulse
width of 10 ps at a wavelength of 1064 nm for potential industrial micromachining applications. The diameters, depths and
morphologies of the drilled craters were studied. Two novel phenomena were found: as hole diameters decreased with fluence,
a change of slope of the trend line indicated a change in ablation mechanism for Al and Ti alloy, metallic materials with
short electron-phonon coupling times (<10 ps), while Au showed no such transition: an isolated island structure was also observed
on Au due to significant melt expulsion. A one-dimensional two-temperature model has been used to discriminate different ablation
phenomena. It is shown that metallic materials with different electron–phonon coupling constant have different ablation characteristics
in the ps regime. This study could be very helpful for metallic material micromachining with high repetition rate ps lasers
pulses which indicates that high throughput may be achieved as well as good machining quality. 相似文献
13.
T. Eidam F. Röser O. Schmidt J. Limpert A. Tünnermann 《Applied physics. B, Lasers and optics》2008,92(1):9-12
We report on the generation of 27 fs pulses with an average output power of 57 W and a repetition rate of 78 MHz. The pulses
are generated by combining a high average power fiber chirped pulse amplification (FCPA) system with a microstructured large-mode-area
fiber for nonlinear compression. The FCPA system delivers 270 fs pulses in a linearly polarized beam with diffraction-limited
quality. Nonlinear compression is achieved by launching the pulses into a short (few cm) piece of microstructured fiber and
subsequent compression by a pair of chirped mirrors.
PACS 42.55.Wd; 42.55.Xi, 42.65.Re 相似文献
14.
A. Fix G. Ehret J. Löhring D. Hoffmann M. Alpers 《Applied physics. B, Lasers and optics》2011,102(4):905-915
A diode-pumped, single-frequency laser system emitting at 935 nm has recently been developed to serve as the transmitter for water vapor differential absorption lidar (DIAL) measurements. This laser uses Nd:YGG (Y3Ga5O12) as the active medium and emits radiation directly at 935 nm without the need of additional frequency conversion processes. The system was diode-pumped at 806 nm and was built up in a master-oscillator-power-amplifier configuration. It generates more than 30 mJ of pulse energy at 100 Hz repetition rate with a beam quality (M 2) of better than 1.4. Since water vapor DIAL demands for stringent requirements of the spectral properties those were carefully investigated in the scope of this paper. Single-frequency operation is achieved by injection seeding and active length control of the oscillator cavity. The range of continuously tunable single-frequency radiation extends to ~0.4 nm centered around 935.31 nm. Values of the spectral purity of >99.996% were determined using long-pass absorption measurements in the atmosphere exceeding the requirements by a large margin. Finally, for the first time water vapor DIAL measurements were performed using a Nd:YGG laser. The reported results show much promise of these directly pumped lasers at 935 nm for future spaceborne but also airborne water vapor lidar systems. 相似文献
15.
X. M. Duan B. Q. Yao G. Li T. H. Wang Y. L. Ju Y. Z. Wang 《Applied physics. B, Lasers and optics》2010,99(3):465-468
A stable output, high power diode-pumped Tm: YLF laser operating at 1908 nm with FWHM line width less than 0.1 nm is reported.
Using a volume Bragg grating, 41.1 W of output with M
2∼2 under an incident pump power of 111.7 W was achieved, corresponding to an optical-to-optical conversion efficiency of 36.8%
and a slope efficiency of 43.2%. A laser wavelength shift of only 0.3 nm with the incident pump power varying from 13.1 W
to 111.7 W was observed. 相似文献
16.
Y. Tao M. S. Tillack S. Yuseph R. Burdt F. Najmabadi 《Applied physics. B, Lasers and optics》2010,99(3):397-400
It was found that the electron density scale length of Sn plasma irradiated with a long duration CO2 laser pulse is much shorter than that predicted by the classical isothermal model. The experimentally observed small dominant
region of in-band (2% bandwidth) 13.5-nm extreme ultraviolet (EUV) emission coincides with this constrained hydrodynamic behavior.
The lower hydrodynamic efficiency may come from the strongly inhibited ablation mass and makes a CO2-laser-produced Sn plasma suitable as an EUV radiation source. 相似文献
17.
This paper reports on the first spectroscopic application of a novel type of GaN blue diode laser emitting around 450 nm, which has recently become available. The diode was characterised and then implemented in an extended cavity, to achieve mode-hop free tuning over a frequency range exceeding 105 GHz. The spectroscopic utility of the device was demonstrated by probing the 52P3/2 to 62S1/2 transition of atomic indium seeded to an atmospheric pressure flame. Single scans over the pressure broadened hyperfine structure were recorded with high signal-to-noise ratios and profiles of the indium LIF distribution through the flame were acquired, at a high spatial resolution. Potential applications of diodes emitting in this spectral region range from industrial sensing to atomic cooling experiments. PACS 42.55.Px; 32.50.+d; 42.62.Fi 相似文献
18.
P. Kumar 《Applied Physics A: Materials Science & Processing》2010,99(1):245-250
Controlled single step fabrication of silicon conical surface modulations on [311] silicon surface is reported utilizing KrF excimer laser [λ=248 nm] at laser fluence below ablation threshold laser fluence. When laser fluence was increased gradually from 0 to 0.2 J/cm2 for fixed 200 numbers of shots; first nanopores are observed to form at 0.1 J/cm2, then very shallow nanocones evolve as a function of laser fluence. At 0.2 J/cm2, nanoparticles are observed to form. Up to 0.15 J/cm2 the very shallow nanocone volume is smaller but increases at a fast rate with laser fluence thereafter. It is observed that the net material volume before and after the laser irradiation remains the same, a sign of the melting and resolidification without any ablation. 相似文献
19.
Theophilos Maltezopoulos Manuel Mittenzwey Armin Azima Jörn Bödewadt Hatem Dachraoui Marie Rehders Christoph Lechner Michael Schulz Marek Wieland Tim Laarmann Jörg Roßbach Markus Drescher 《Applied physics. B, Lasers and optics》2014,115(1):45-54
Direct seeding with a high-harmonic generation (HHG) source can improve the spectral, temporal, and coherence properties of a free-electron laser (FEL) and shall reduce intensity and arrival-time fluctuations. In the seeding experiment sFLASH at the extreme ultraviolet FEL in Hamburg FLASH, which operates in the self-amplified spontaneous emission mode (SASE), the 21st harmonic of an 800 nm laser is refocused into a dedicated seeding undulator. For seeding, the external light field has to overcome the noise level of SASE; therefore, an efficient coupling between seed pulse and electron bunch is mandatory. Thus, an HHG beam with a proper divergence, width, beam quality, Rayleigh length, pointing stability, single-shot pulse energy, and stability in the 21st harmonic is needed. Here, we present the setup of the HHG source that seeds sFLASH at 38.1 nm, the optimization procedures, and the necessary diagnostics. 相似文献
20.
Quantum electrodynamics in a laser and the electron laser collisionQuantum electrodynamics in a laser and the electron laser collision 下载免费PDF全文
Quantum electrodynamics in a laser is formulated, in which the electron-laser interaction is exactly considered, while the interaction of an electron and a single photon is considered by perturbation. The formulation is applied to the electron- laser collisions. The effect of coherence between photons in the laser is therefore fully considered in these collisions. The possibility of y-ray laser generation by use of this kind of collision is discussed. 相似文献