共查询到20条相似文献,搜索用时 31 毫秒
1.
Jerome P. Ferrance Kenith E. Meissner John W. Pettit 《Journal of nanoparticle research》2010,12(2):405-415
Optical signals were used to modulate the resistance of single-walled carbon nanotube–polymer composite films for development
of optical switching devices. Films were fabricated from nanotubes dispersed in poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene)
(MEH-PPV) solutions in either tetrahydrofuran (THF) or toluene. MEH-PPV was affected by the solvent choice, with THF causing
an absorbance shift to shorter wavelengths. Composite films formed from THF dispersions showed 1–4% resistance decreases when
illuminated with a green diode laser. Illumination of toluene-based films showed up to 5.4% resistance decreases, smaller
than expected based on the polymer solution absorbance. Fluorescent emission from the polymer in toluene appears to inhibit
charge transfer from the polymer to the nanotubes. THF films were unaffected by illumination with a red diode laser, while
toluene dispersion films showed resistance decreases up to 1%. Nanotube dispersion and film formation reproducibility, evaluated
for both the solvents, showed that the solvent affected film resistance and dispersion stability. 相似文献
2.
We report a linearly polarized Tm doped fiber laser. The fiber laser was set up by using a piece of polarization maintaining
Tm doped double clad fiber of 5 m length as gain medium and a polarization beam splitter as a polarization selector. The fiber
laser was pumped by a fiber pigtailed laser diode working at 790 nm with a maximum output power of 90 W. The linearly polarized
Tm laser operated at wavelength around 2030 nm. A maximum output power up to 21.9 W was achieved when the pump power was 63.27
W with a threshold of 11.92 W, a slope efficiency of about 43.7%, and a polarization extinction ratio of 92.7% (11.37 dB).
In addition to the blue fluorescence, we also observed the violet fluorescence under high pump power level. The up-conversion
fluorescence was considered to be attributed to the 1
G
4 → 3
H
6, and 1
D
2 → 3
F
4 transitions of Tm ions, respectively. 相似文献
3.
We have studied the Amplified Spontaneous Emission (ASE) characteristics of the conjugated copolymer poly{[2-[2′,5′-bis(2″-ethylhexyloxy)phenyl]-1,4-phenylenevinylene]-co-[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene]} (BEHP-co-MEH-PPV) in a few organic solutions under optical pumping by the third harmonic of Nd:YAG (355 nm). The results show that in BEHP-co-MEH-PPV, the BEHP-PPV component is capable of forcing MEH-PPV to produce ASE at 560 nm, which appears to arise out of the non-excimeric state of MEH-PPV.The ASE of BEHP-co-MEH-PPV was also compared with the conventional laser dyes Rhodamine B (Rh B), Rhodamine 6G (Rh 6G), and also the new laser material MEH-PPV. 相似文献
4.
F. Kong X.L. Wu G.S. Huang R.K. Yuan C.Z. Yang P.K. Chu G.G. Siu 《Applied Physics A: Materials Science & Processing》2006,84(1-2):203-206
We report the temperature-dependent photoluminescence (PL) behavior of two poly (p-phenylene-vinylene) derivatives with different backbones, a homopolymer poly-[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene-vinylene] (MEH-PPV) and a copolymer poly-{[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene]-alt-[2,5-diphenylene-1,3,4-oxadiazole-vinylene]} (MEH-OPPV). The PL peak positions of the MEH-PPV in both solid solution and film are blue shifted with increasing measurement temperature because the thermally induced torsion and libration modes reduce the conjugation lengths of the polymer, but the shift rate is smaller in the MEH-PPV film than that in the solid solution. The PL peak position of the MEH-OPPV film is independent of measurement temperature because there is a large dihedral angle between the adjacent monomer units. The large dihedral angle increases the conformational disorder to eliminate the effect of the disorder induced by the thermally induced torsion and libration modes on the conjugation lengths of the MEH-OPPV. PACS 73.61.Ph; 78.55.Kz 相似文献
5.
L.F.L. Costa J.C.S. Moraes F.C. Cruz R.C. Viscovini D. Pereira 《Applied physics. B, Lasers and optics》2007,86(4):703-706
We report 12 new THz (far-infrared) laser lines from methanol (CH3OH), ranging from 58.1 μm (5.2 THz) to 624.6 μm (0.5 THz). A 13CO2 laser of wide tunability (110 MHz) has been used for optical pumping, allowing access to previously unexplored spectral regions.
Optoacoustic absorption spectra were used as a guide to search for new THz laser lines, which have been characterized in wavelength,
polarization, offset, relative intensity, and optimum operation pressure. For 20 laser lines previously observed, we have
measured the absorption offset with respect to the 13CO2 laser line center.
PACS 33.20.Ea; 33.20.Vq; 33.80.-b 相似文献
6.
Soluble multi-walled carbon nanotubes (MWNTs) have been obtained by noncovalent modification with poly [2-methoxy,5-(2′-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV). For the composite MWNT/MEH-PPV, there is π-π interaction between the MEH-PPV and MWNTs in addition to the wrapping of the polymer. The nonlinear optical transmittance was measured using a nanosecond optical parametric oscillator pumped with a Nd:YAG system. Excellent optical limiting performance of the composite MWNT/MEH-PPV was observed both in the visible region of 590-680 nm and at the wavelength of 1064 nm. By means of time-correlated single-photon counting fluorescence measurement, an explanation based on the nonlinear absorption of MWNT dominated by the intermolecular energy transfer was proposed. 相似文献
7.
We have studied the amplified spontaneous-emission characteristics (ASE) of conjugated poly[2-methoxy-5-(2-ethylhexyloxy)1,4-phenylenevinylene] MEH-PPV in a few organic solutions. The ASE of MEH-PPV appears to arise from its excimeric state. This is perhaps the first report, to the best of our knowledge, on an excimeric-liquid state laser. MEH-PPV in solutions of benzene or tetrahydrofuran (THF) was pumped by the second and third harmonics of an Nd:YAG (532 and 355 nm) for different pump-pulse energies. The ASE of MEH-PPV was compared with the conventional laser dyes Rhodamine B (Rh B) and Rhodamine 6G (Rh 6G). The most important and distinguishing features are: (a) MEH-PPV has a four-times better photochemical stability than Rh B or Rh 6G; (b) the threshold and concentration for the laser action in MEH-PPV is far less than Rh B or Rh 6G. 相似文献
8.
V.B. Tiwari S. Singh S.R. Mishra H.S. Rawat S.C. Mehendale 《Applied physics. B, Lasers and optics》2006,83(1):93-96
We report on a Doppler-free polarization spectroscopy based technique of laser frequency stabilization using a balanced bi-polarimeter
set-up. Two linearly polarized weak laser beams are used to probe birefringence induced by two oppositely circularly polarized
strong pump beams in a vapour cell. Subtraction of balanced polarimeter signals obtained from the two probe beams results
in a background-free dispersion-like reference signal without frequency modulation. The dispersion-like signal corresponding
to the closed transition 5 2
S
1/2 (F=2) →5 2
P
3/2 (F′=3) of 87Rb was used for frequency locking of a diode laser. The frequency fluctuations and the drift were measured to be less than
0.25 MHz and 0.02 MHz, respectively, for an observation period of more than 10 hours.
PACS 42.62.Fi; 42.55.Px; 32.30.-r 相似文献
9.
The conjugated polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) is an important electrooptical material, which is useable as an excellent laser media. In this paper, we present the absorption and fluorescence spectral characteristics of MEH-PPV in a few organic solvents. The paper shows that MEH-PPV exists in an excimeric state in benzene, and that the laser action as shown here arises from a liquid excimeric state. 相似文献
10.
M. L. Du 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,38(3):533-536
We derive a formula using closed-orbit theory for the photodetachment cross-section of H- in the presence of a static electric field when there is an arbitrary angle θL between the laser polarization direction and the static electric field. This formula generalizes the previous result for
laser polarization parallel to the static electric field, the effect of laser polarization direction appears as a factor cos2(θL) in the amplitude of the oscillation. A photodetachment cross-section formula valid above and below detachment threshold
is proposed. 相似文献
11.
M. Schnürer S. Ter-Avetisyan H. Stiel U. Vogt W. Radloff M. Kalashnikov W. Sandner P.V. Nickles 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(3):331-335
Using 50 fs ( ∼ 2×1018 W/cm2) and 2 ps ( ∼ 5×1016 W/cm2) pulses from a Ti:Sa multi-TW laser at 800 nm wavelength large Xe-clusters ( 105...106 atoms per cluster) have been excited. Absolute yield measurements of EUV-emission in a wavelength range between 10 nm and
15 nm in combination with cluster target variation were carried out. The ps-laser pulse has resulted in about 30% enhanced
and spatially more uniform EUV-emission compared to fs-laser excitation. Circularly polarized laser light instead of linear
polarization results in enhanced emission which is probably caused by electrons gaining higher energies by the polarization
dependent optical field ionization process. An absolute emission efficiency at 13.4 nm of up to 0.8% in 2π sr and 2.2% bandwidth
has been obtained.
Received 11 January 2001 and Received in final form 27 March 2001 相似文献
12.
The beam propagation factor, M2 of the master-oscillator power-amplifier (MOPA) CuBr laser emission compliant with ISO 11146 is studied methodically. Statistical
parameters of 2D intensity profile of the near and far fields of MOPA laser radiation are measured by a beam analyzing technique
as functions of timing delay between MO and PA. For first time the influence of the gas buffer (causing the radiation profile
to change from annular to top-hat and Gaussian-like) and light polarization on CuBr laser beam focusability (M2) was under investigation. The MOPA gain curve is found and the influence of gain on the input signal (from MO into PA) due
to the absorption/amplification in PA on the field profiles is shown. For annular radiation M2 range is from 13–14 (small delays) to 5–6 (large delays) and for filled-center radiation M2 is 6–7 (small delays) and at the end of gain curve is as much as 4. With polarized light, M2 drops to 3 at the end of gain curve. The brightness of laser emission with hydrogen goes up 3–5 times and the linearly-polarized
beam is at least 40% brighter than that of partial or non-polarized beams. 相似文献
13.
N.?Whiting P.?Nikolaou N.?A.?Eschmann M.?J.?Barlow R.?Lammert J.?Ungar W.?Hu L.?Vaissie B.?M.?Goodson
Next-generation laser diode arrays with integrated ‘on-chip’ volume holographic gratings can provide high power with spectrally
narrowed output that can be tuned about the rubidium D1 line—without causing significant changes to the laser’s flux or spectral profile. These properties were exploited to independently
evaluate the effects of varying the laser centroid wavelength and power on batch-mode Rb/129Xe spin-exchange optical pumping (SEOP) as functions of xenon partial pressure and cell temperature. Locally optimized SEOP
was often achieved with the laser tuned to either the red or blue side of the Rb D1 line; global optimization of SEOP was observed at lower cell temperatures and followed the D1 absorption profile, which was asymmetrically broadened and red-shifted from the nominal wavelength. The complex dependence
of the optimal wavelength for laser excitation on the cell temperature and Xe density appears to result from an interplay
between cell illumination and the Rb/129Xe spin-exchange rate, as well as [Xe]cell-dependent changes to the Rb absorption lineshape that are in qualitative agreement with expectations based on previous work
[Romalis et al., Phys. Rev. A, 56:4569–4578, (1997)], but significantly greater in magnitude. These next-generation lasers provide a ∼2–3-fold improvement in 129Xe polarization compared to conventional broadband lasers. 相似文献
14.
采用与信标发射接收系统参数匹配的长脉冲光源,可在脉冲回光时间内产生较亮星等的钠信标,既有利于提高信标探测的信噪比,也有利于实现自适应光学系统的高频闭环校正.基于450 mm直径望远镜和大能量长脉冲光源,开展了钠信标探测实验,得到了长脉冲光源产生的钠信标回光特性.通过CCD和光电倍增管,采集得到了不同发射能量、出射偏振态下的回光强度,并获得了最大强度为15万光子/m2/pulse的回光,对应脉冲回光时间内约4.1等星的亮度.分析推算了实验条件下钠原子的柱密度.实验全过程未出现明显的饱和现象,验证了采用长脉冲钠信标光源避免饱和效应、得到高亮度钠信标的可行性. 相似文献
15.
Using pulsed laser with different wavelengths, transient photovoltage (TPV) is investigated for the sandwich device of indium tin oxide (ITO)/poly (2-methoxy-5-(2′-ethylhexyloxy)-1, 4-phenylenevinylene) (MEH-PPV) (500 nm)/Al. At laser wavelength of 500 nm, a 0.1 millisecond negative TPV signal appears followed by a positive one lasting 40-80 milliseconds. With increasing laser wavelength, the negative signal becomes weak and disappears when wavelengths λ?560 nm. This work demonstrates the process of exciton dissociation at the interface between ITO and MEH-PPV. A new method measuring the relative dissociation rate at the interface between polymer and electrode is introduced. It is estimated that the dissociation rate at Al interface is 4-8 times of that at the ITO interface. 相似文献
16.
Kinetic, spectral, intensity, angular, and polarization of resonant two-photon absorption (TPA) in β-CdP2 has been investigated. Resonant TPA was observed for which the total energy of the two photons was 2.60 eV. It is shown that
resonant TPA takes place via a real intermediate level d
3 in the band gap at the depth E
c-0.86 eV. The electron transverse relaxation time for resonant TPA, the cross section for absorption of laser photons in d
3→C transitions, the equilibrium population of d
3 centers in a doped n-type sample, and the resonant TPA constant were determined as 4.3×10−14 s, 1.25×10−17 cm2, 0.95, and 0.028 cm/MW, respectively.
Fiz. Tverd. Tela (St. Petersburg) 40, 1252–1256 (July 1998) 相似文献
17.
Michal Novotn?? P??emysl Fitl Anna Krasilnikova Sytchkova Ji???- Bul?-?? Jan Lanaok Petr Pokorna David Najdek Jia Boan 《Central European Journal of Physics》2009,7(2):327-331
The effect of pulsed laser treatment of metal, and metal blacks, was studied. Gold and black gold thin films were fabricated
by thermal evaporation of gold in a vacuum and nitrogen atmosphere respectively. Black gold films were grown in a nitrogen
atmosphere at pressures of 200 Pa and 300 Pa. UV pulsed laser radiation (λ = 266 nm, τ = 4 ns), with fluence ranging from 1 mJ·cm−2 to 250 mJ·cm−2 was used for the film treatment in a vacuum and nitrogen atmosphere. The nitrogen pressure was varied up to 100 kPa. Surface
structure modifications were analyzed by optical microscopy, atomic force microscopy (AFM) and scanning electron microscopy
(SEM). Energy dispersive X-ray spectroscopy (EDX) was used for chemical characterization of the samples. A significant dependence
of the film optical and structural properties on laser treatment conditions (laser fluence, ambient pressure and number of
applied pulses) was found. The threshold for observable damage and initiation of changes of morphology for gold and black
gold surfaces was determined. Distinct modifications were observed for fluences greater than 106 mJ·cm−2 and 3.5 mJ·cm−2 for the gold and black gold films respectively. Absorbtivity of the black gold film is found to decrease with an increase
in the number of laser pulses. Microstructural and nanostructural modifications after laser treatment of the black gold film
were observed. EDX analysis revealed that no impurities were introduced into the samples during both the deposition and laser
treatment.
相似文献
18.
The polarization states of 〈111〉-cut Yb:YAG crystal microchip lasers were investigated by pumped with the elliptically polarized
pump beam from fiber-coupled laser-diode. The manipulated polarized lasers were achieved in laser-diode pumped Yb:YAG microchip
laser by controlling the crystalline-orientations in 〈111〉-growth Yb:YAG crystal. Generally elliptically polarized lasers
were obtained in laser-diode pumped Yb:YAG microchip lasers. However, crystalline-orientation manipulated linearly polarized
laser was obtained when six different sites with different crystalline orientations were set to parallel to the major axis
direction of the elliptically polarized pump beam. Six different sites in Yb:YAG crystal were separated with 30° and 90°,
which were responsible for the linearly polarized laser oscillations. Circularly polarized lasers were observed when a Yb:YAG
crystal was aligned to a special position between two sites responsible for linearly polarized laser oscillation. Effects
of the polarization states of pump source on the laser polarization states of Yb:YAG microchip lasers and polarization direction
of different polarized lasers with respect to Yb:YAG crystal rotation was addressed. 相似文献
19.
We present an environmentally-stable picosecond Yb-doped fiber laser by employing an achromatic quarter-wave-plate (AQWP)
as a pulse stabilizer in the all-normal-dispersion and polarization-maintaining linear laser cavity. It is shown that the
AQWP plays a critical role to control both the polarization state and spectral filtering of the proposed mode-locked laser.
The demonstrated laser generates 2-ps-long pulses with pulse energies of 1 nJ at a repetition rate of 117 MHz and parabolic
spectral width of 26 nm. The fundamental RF carrier frequency exhibits Allan deviation of 3.8 × 10−8 at 1-s averaging time and phase noise of −95 dBc/Hz at 10-Hz offset frequency. 相似文献
20.
Y. J. Chen Y. F. Lin X. H. Gong H. M. Zhu Z. D. Luo Y. D. Huang 《Applied physics. B, Lasers and optics》2010,98(1):55-60
End-pumped by a single-stripe 805-nm diode laser, a maximum continuous-wave output power of 290 mW with slope efficiency of
42% and 90 mW with slope efficiency of 44% around 2 μm were achieved in a 1.6-mm-thickness, unprocessed 7.2 at.% Tm3+:BaGd2(MoO4)4 cleavage plate in a hemispherical and plano–plano cavities, respectively, when the absorbed pump power was 830 mW. The dependence
of the polarization of output laser on the output coupler transmission was investigated. The influence of upconversion on
the laser performance was analyzed. The results show that the unprocessed Tm3+:BaGd2(MoO4)4 cleavage plate is a promising 2-μm laser gain medium pumped by diode laser around 808 nm. 相似文献