共查询到20条相似文献,搜索用时 312 毫秒
1.
M. S. Gaponenko I. A. Denisov V. E. Kisel A. M. Malyarevich A. A. Zhilin A. A. Onushchenko N. V. Kuleshov K. V. Yumashev 《Applied physics. B, Lasers and optics》2008,93(4):787-791
Glass doped with PbS quantum dots is presented as a saturable absorber (SA) for a passive Q-switching of a diode-pumped 1.9 μm Tm:KYW laser. Output pulses with energy of 44 μJ at a repetition rate of 2.5 kHz with
an average output power of 110 mW were obtained. The Q-switching conversion efficiency was 33%. The absorption saturation intensity of the glass doped with PbS quantum dots with
a mean radius of 5.2 nm at a wavelength of 2 μm was measured to be 1.5 MW/cm2. 相似文献
2.
We have theoretically investigated the thermal characteristics of double-channel ridge–waveguide InGaAs/InAlAs/InP quantum
cascade lasers (QCLs) using a two-dimensional heat dissipation model. The temperature distribution, heat flow, and thermal
conductance (G
th) of QCLs were obtained through the thermal simulation. A thick electroplated Au around the laser ridges helps to improve
the heat dissipation from devices, being good enough to substitute the buried heterostructure (BH) by InP regrowth for epilayer-up
bonded lasers. The effects of the device geometry (i.e., ridge width and cavity length) on the G
th of QCLs were investigated. With 5 μm thick electroplated Au, the G
th is increased with the decrease of ridge width, indicating an improvement from G
th=177 W/K⋅cm2 at W=40 μm to G
th=301 W/K⋅cm2 at W=9 μm for 2 mm long lasers. For the 9 μm×2 mm epilayer-down bonded laser with 5 μm thick electroplated Au, the use of InP
contact layer leads to a further improvement of 13% in G
th, and it was totally raised by 45% corresponding to 436 W/K⋅cm2 compared to the epilayer-up bonded laser with InGaAs contact layer. It is found that the epilayer-down bonded 9 μm wide BH
laser with InP contact layer leads to the highest G
th=449 W/K⋅cm2. The theoretical results were also compared with available obtained experimentally data. 相似文献
3.
Tunable diode-laser absorption of CO2 near 2.7 μm incorporating wavelength modulation spectroscopy with second-harmonic detection (WMS-2f) is used to provide a
new sensor for sensitive and accurate measurement of the temperature behind reflected shock waves in a shock-tube. The temperature
is inferred from the ratio of 2f signals for two selected absorption transitions, at 3633.08 and 3645.56 cm−1, belonging to the ν
1+ν
3 combination vibrational band of CO2 near 2.7 μm. The modulation depths of 0.078 and 0.063 cm−1 are optimized for the target conditions of the shock-heated gases (P∼1–2 atm, T∼800–1600 K). The sensor is designed to achieve a high sensitivity to the temperature and a low sensitivity to cold boundary-layer
effects and any changes in gas pressure or composition. The fixed-wavelength WMS-2f sensor is tested for temperature and CO2 concentration measurements in a heated static cell (600–1200 K) and in non-reactive shock-tube experiments (900–1700 K) using
CO2–Ar mixtures. The relatively large CO2 absorption strength near 2.7 μm and the use of a WMS-2f strategy minimizes noise and enables measurements with lower concentration,
higher accuracy, better sensitivity and improved signal-to-noise ratio (SNR) relative to earlier work, using transitions in
the 1.5 and 2.0 μm CO2 combination bands. The standard deviation of the measured temperature histories behind reflected shock waves is less than 0.5%.
The temperature sensor is also demonstrated in reactive shock-tube experiments of n-heptane oxidation. Seeding of relatively
inert CO2 in the initial fuel-oxidizer mixture is utilized to enable measurements of the pre-ignition temperature profiles. To our
knowledge, this work represents the first application of wavelength modulation spectroscopy to this new class of diode lasers
near 2.7 μm. 相似文献
4.
Albert?Mihranyan Mortadha?Muhel Maria?Str?mme 《Applied Physics A: Materials Science & Processing》2009,94(2):299-305
The dissolution process of sparingly soluble CaCO3 microparticles and how the fractal surface dimension of the particles changes during dissolution is analyzed. The particles
and the dissolution process are studied using scanning electron microscopy, X-ray diffraction, nitrogen adsorption, laser
diffraction and conductance measurements. Ball milling of the particles is shown to maintain the particle crystallinity, and
to introduce an increased fractal surface dimension in the 1–10 μm size range. Dissolution is found to increase the surface
dimension of initially smooth particles and to maintain the fractal surface roughness of milled particles. The dissolution
process increases the relative number of small particles (50 nm–1 μm) whereas the larger ones decrease in size. The solubility
of the milled fractal particles was ∼1.8 times higher than that for the initially smooth ones. The presented findings show
that developing methods for increasing the fractal surface roughness of particles should be of interest for improving the
solubility of poorly soluble drug candidates. 相似文献
5.
High-resolution infrared polarization spectroscopy (IR-PS) and degenerate four wave mixing (IR-DFWM) spectroscopy of methane
using a diode-seeded modeless laser (DSML) system are reported. Mid-infrared radiation around 3.3 μm is generated by difference
frequency mixing of the single-mode output of the DSML around 0.634 μm with the frequency-doubled output of a single-mode
Nd:YAG pump laser at 0.532 μm. Polarization spectroscopy signals in the forward geometry were generated in methane at around
5 Torr pressure. IR-PS spectra were recorded with a typical signal-to-noise ratio of 150:1 with methane pressures of at least
1 Torr. The line shape of the IR-PS signals was analysed to measure pressure broadening induced by nitrogen buffer gas yielding
a value of 6.3±1.5 MHz Torr−1. IR-DFWM spectra of methane were generated in the counter-propagating pump geometry yielding Doppler-free signals with signal-to-noise
ratios of typically 650:1. Signals were obtained at methane pressures down to less than 10 mTorr. A comparison of IR-PS and
IR-DFWM is made indicating that IR-DFWM has some advantages over IR-PS in this spectral region in terms of sensitivity, signal-to-noise
ratio and ease of use. The results illustrate the utility of the DSML for high-resolution nonlinear spectroscopy in the mid
infrared. 相似文献
6.
High-resolution photorefractive gratings in nematic liquid crystals sandwiched with photoconductive polymer film 总被引:1,自引:1,他引:0
F. Yao Y. Pei Yu Zhang J. Zhang C. Hou X. Sun 《Applied physics. B, Lasers and optics》2008,92(4):573-576
Photorefractive gratings with high grating resolution were observed in the 20 μm thick low-molar-mass nematic liquid crystal
(NLC) cell with a separate photoconductive (PC) poly(N-vinylcarbazole) layer. An orientational grating with a grating spacing of 1.9 μm was produced. It is believed that a space–charge
field with small fringe spacing forms in the PC layer and its evanescent component penetrates into the NLC layer. The penetrated
evanescent field drives the NLC to reorient, and consequently the orientational grating forms. The model indicates that the
modulated field exists in several hundred nanometers near the surface, and thus the orientational grating is not full of the
NLC film, which is consistent with the observed phenomena of the multiple diffractions. Besides, asymmetric two-beam coupling
of 11.2% was achieved for the grating with a grating spacing of 1.9 μm, and a net gain coefficient of larger than 62 cm−1 was obtained. 相似文献
7.
M. Wu E. Gu A. Zarowna A. L. Kanibolotsky A. J. C. Kuehne A. R. Mackintosh P. R. Edwards O. J. Rolinski I. F. Perepichka P. J. Skabara R. W. Martin R. A. Pethrick D. J. S. Birch M. D. Dawson 《Applied Physics A: Materials Science & Processing》2009,97(1):119-123
Star-shaped oligofluorene consists of highly-fluorescent macromolecules of considerable interest for organic electronics.
Here, we demonstrate controlled micro-patterning of these organic nanostructured molecules by blending them with custom-synthesized
photo-curable aliphatic polymer matrices to facilitate solventless inkjet printing. The printed microstructures are spherical
with minimum dimensions of 12 μm diameter and 1 μm height when using a cartridge delivering ∼1 pL droplets. We evaluate the
physical characteristics of the printed structures. Photoluminescence studies indicate that the blend materials possess similar
fluorescence properties to neat materials in solid films or toluene solution. The fluorescence lifetime consists of two components,
respectively 0.68±0.01 ns (τ
1) and 1.23±0.12 ns (τ
2). This work demonstrates that inkjet printing of such blends provides an attractive method of handling fluorescent nano-scaled
molecules for photonic and optoelectronic applications. 相似文献
8.
Al-2 wt% Li alloy was prepared using metals of 99.99% high purity in the vacuum atmosphere. The bulk samples were directionally
solidified upward with a constant growth rate, V, (∼8.30 μm/s) and different temperature gradients, G, (3.11–6.06 K/mm) and also with a constant G (6.06 K/mm) and different V (8.3–164.70 μm/s) in the directional solidification apparatus. The cellular spacings, λ, were measured from both transverse and longitudinal section of the specimens and expressed as functions of solidification
processing parameters, G and V, by using a linear regression analysis. The effects of the G and V on λ, were investigated. The experimental results were compared with the current theoretical and numerical models, and similar
previous experimental results. 相似文献
9.
U.?B?yük N.?Mara?l? H.?Kaya E.??ad?rl? K.?Ke?lio?lu 《Applied Physics A: Materials Science & Processing》2009,95(3):923-932
Al–Cu–Ag alloy was prepared in a graphite crucible under a vacuum atmosphere. The samples were directionally solidified upwards
under an argon atmosphere with different temperature gradients (G=3.99–8.79 K/mm), at a constant growth rate (V=8.30 μm/s), and with different growth rates (V=1.83–498.25 μm/s), at a constant gradient (G=8.79 K/mm) by using the Bridgman type directional solidification apparatus. The microstructure of Al-12.80-at.%–Cu-18.10-at.%–Ag
alloy seems to be two fibrous and one lamellar structure.
The interlamellar spacings (λ) were measured from transverse sections of the samples. The dependence of interlamellar spacings (λ) on the temperature gradient (G) and the growth rate (V) were determined by using linear regression analysis. According to these results it has been found that the value of λ decreases with the increase of values of G and V. The values of λ
2
V were also determined by using the measured values of λ and V. The experimental results were compared with two-phase growth from binary and ternary eutectic liquid. 相似文献
10.
M.?Silies H.?Witte S.?Linden J.?Kutzner I.?Uschmann E.?F?rster H.?Zacharias 《Applied Physics A: Materials Science & Processing》2009,96(1):59-67
The interaction of ultrashort laser pulses with solid state targets is studied concerning the production of short X-ray pulses
with photon energies up to about 10 keV. The influence of various parameters such as pulse energy, repetition rate of the
laser system, focusing conditions, the application of prepulses, and the chirp of the laser pulses on the efficiency of this
highly nonlinear process is examined. In order to increase the X-ray flux, the laser pulse energy is increased by a 2nd multipass
amplifier from 750 μJ to 5 mJ. By applying up to 4 mJ of the pulse energy a X-ray flux of 4×1010 Fe K
α
photons/s or 2.75×1010 Cu K
α
photons/s are generated. The energy conversion efficiency is therefore calculated to η
Fe≈1.4×10−5 and η
Cu≈1.0×10−5. The X-ray source size is determined to 15×25 μm2. By focusing the produced X-rays using a toroidally bent crystal a quasi-monochromatic X-ray point source with a diameter
of 56 μm×70μm is produced containing ≈104 Fe K
α1 photons/s which permits the investigation of lattice dynamics on a picosecond or even sub-picosecond time scale. The lattice
movement of a GaAs(111) crystal is shown as a typical application. 相似文献
11.
An optical clock based on an Er3+ fiber femtosecond laser and a two-mode He–Ne/CH4 optical frequency standard (λ=3.39 μm) is realized. Difference-frequency generation is used to down convert the 1.5-μm frequency comb of the Er3+ femtosecond laser to the 3.4-μm range. The generated infrared comb overlaps with the He–Ne/CH4 laser wavelength and does not depend on the carrier–envelope offset frequency of the 1.5-μm comb. In this way a direct phase-coherent
connection between the optical frequency of the He–Ne/CH4 standard and the radio frequency pulse repetition rate of the fiber laser is established. The stability of the optical clock
is measured against a commercial hydrogen maser. The measured relative instability is 1×10−12 at 1 s and for averaging times less than 50 s it is determined by the microwave standard, while for longer times a drift
of the He–Ne/CH4 optical standard is dominant. 相似文献
12.
Study on the p-type QWIP-LED device 总被引:1,自引:1,他引:0
A p-type quantum well infrared photodetector (QWIP) integrated with a light-emitting diode (LED) (named QWIP-LED) was fabricated
and studied. The infrared photo-response spectrum was obtained from the device resistance variation and the near-infrared
photo-emission intensity variation. A good agreement between these two spectra was observed, which demonstrates that the long-wavelength
infrared radiation around 7.5 μm has been transferred to the near-infrared light at 0.8 μm by the photo-electronic process
in the QWIP-LED structure. Moreover, the experimentally observed infrared response wavelength is in good agreement with the
theoretical calculation value of 7.7 μm. The results on the upconversion of the infrared radiation will be very useful for
the new infrared focal plane array technology. 相似文献
13.
Etienne Shaffer Amr S. Helmy Dominique Drouin Jan J. Dubowski 《Applied Physics A: Materials Science & Processing》2008,93(4):869-874
We have investigated ArF (λ=193 nm) excimer laser-induced crystallization of amorphous CdSe semiconductor thin films. The crystallization has been monitored
by a related photoluminescence emission in the free-exciton and defect-band transition regions. For different irradiation
conditions, we have observed formation of nanorods, up to 2 μm long, as well as the formation of arrays of CdSe nanobeads
with a narrow size distribution and characteristic dimensions corresponding to λ/2 and λ/8. The successful crystallization has also been confirmed by confocal Raman spectroscopy. 相似文献
14.
Liu L. Loh N. H. Tay B. Y. Tor S. B. Yin H. Q. Qu X. H. 《Applied Physics A: Materials Science & Processing》2011,103(4):1145-1151
Micro powder injection molding (μPIM) has been developed as a potential technique for mass production of microcomponents in microsystems due to its shaping
complexity at low cost, in which sintering is a crucial step to dictate the final properties of the microcomponents. In this
paper, final-stage sintering behavior of 316L stainless steel microsize structures prepared by μPIM, φ100 μm and φ60 μm, respectively, was studied. The effect of size reduction in the regime of micrometers on the density of various microsize
structures was investigated. Sintering kinetics of the microsize structures of φ100 μm and φ60 μm were studied based on particle level sintering models. It is found that the microsize structures of φ60 μm had higher density than the microsize structures of φ100 μm given the same sintering condition. The results indicate that size reduction in the regime of micrometers facilitated
densification of microsize structures. The grain growth mechanism of microsize structures varied with size. Whereas the grain
growth of the microsize structures of φ100 μm is governed by surface-diffusion-controlled pore drag, the grain growth of the microsize structures of φ60 μm is controlled by boundary diffusion. During densification, the microsize structures, φ100 μm and φ60 μm, are both controlled by lattice diffusion. The corresponding activation energies are reported in the paper. 相似文献
15.
J. S. Yu S. Slivken A. Evans M. Razeghi 《Applied Physics A: Materials Science & Processing》2008,93(2):405-408
High-temperature, high-power, and continuous-wave (CW) operation of quantum-cascade lasers with 35 active/injector stages
at λ∼8.85 μm above room temperature is achieved without using a buried heterostructure. At this long wavelength, the use of a
wider ridge waveguide in an epilayer-down bonding scheme leads to a superior performance of the laser. For a high-reflectivity-coated
21 μm×3 mm laser, the output power of 237 mW and the threshold current density of 1.44 kA/cm2 at 298 K under CW mode are obtained with a maximum wall-plug efficiency of 1.7%. Further improvements were observed by using
a 4-mm-long cavity. The device exhibits 294 mW of output power at 298 K and it operates at a high temperature, even up to
358 K (85°C). The full widths at half-maximum of the laser beam in CW operation for the parallel and the perpendicular far-field
patterns are 25°and 63°, respectively. 相似文献
16.
We report on monitoring of nitric oxide (NO) traces in human breath via infrared cavity leak-out spectroscopy. Using a CO
sideband laser near 5 μm wavelength and an optical cavity with two high-reflectivity mirrors (R=99.98%), the minimum detectable absorption is 2×10−10 cm−1 Hz1/2. This allows for spectroscopic analysis of rare NO isotopologues with unprecedented sensitivity. Application to simultaneous
online detection of 14NO and 15NO in breath samples collected in the nasal cavity is described for the first time. We achieved a noise-equivalent detection
limit of 7 parts per trillion for nasal 15NO (integration time: 70 s). 相似文献
17.
S. D. Pan X. Q. Yu Z. Yan Y. Shen X. J. Lv S. N. Zhu 《Applied physics. B, Lasers and optics》2008,93(4):749-752
We present an approach to generating a tunable orange laser from 0.601 to 0.604 μm based on a quasi-periodically poled superlattice
in LiTaO3 and a Q-switched 1.064 μm Nd:YVO4 laser as pump. The orange laser was generated in a cavity by a parametric process cascaded by a frequency mixing with a maximum
output of 310 mW using 15 W pump power. 相似文献
18.
19.
C. K. Chung Y. C. Sung G. R. Huang E. J. Hsiao W. H. Lin S. L. Lin 《Applied Physics A: Materials Science & Processing》2009,94(4):927-932
Pyrex glass etching is an important technology for the microfluid application to lab-on-a-chip devices, but suffers from very
low etching rate and mask-requiring process in conventional HF/BOE wet or plasma dry etching as well as thermal induced crack
surface by CO2 laser processing. In this paper, we applied the liquid-assisted laser processing (LALP) method for linear through-wafer deep
etching of Pyrex glass without mask materials to obtain a crackless surface at very fast etching rates up to 25 μm/s for a
20 mm long trench. The effect of laser scanning rate and water depth on the etching of the 500 μm thick Pyrex glass immersed
in liquid water was investigated. The smooth surface without cracks can be achieved together with the much reduced height
of bulge via an appropriate parameter control. A mechanism of thermal stress reduction in water and shear-force-enhanced debris
removal is discussed. The quality improvement of glass etching using LALP is due to the cooling effect of the water to reduce
the temperature gradient for a crackless surface and natural convection during etching to carry away the debris for diminishing
bulge formation.
An erratum to this article can be found at 相似文献
20.
Zongqing Ma Yongchang Liu Zhizhong Dong Liming Yu Zhiming Gao Qian Zhao 《Applied Physics A: Materials Science & Processing》2009,96(4):975-978
Based on the phase identification and microstructural observation, it is found that the Cu addition in the μm-SiC-doped samples
could depress the reaction between Mg and SiC and thus decrease the amount of both C substitution for B and the Mg2Si nanoparticles. As a result, compared to the only μm-SiC-doped MgB2 sample, the T
c
of the Cu and μm-SiC multi-doped MgB2 sample is improved and the J
c
in high fields is deteriorated. 相似文献