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J. Seres J. Klebniczki E. Seres J. Hebling 《Applied physics. B, Lasers and optics》1998,67(5):569-572
Received: 1 April 1998/Revised version: 20 April 1998 相似文献
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In the case of cw Gaussian illumination, the thermo-optical n2 cannot be characterised by a constant value. It is shown that, if absorption has both linear and nonlinear contributions, the thermo-optical n2 consists of a position- and power-dependent term. Hence analytical formulae that assume a constant n2 are no longer valid for the Z-scan fitting. In this paper a new Z-scan theory is introduced, which is applicable to the thermo-optical effect in the presence of both linear and nonlinear absorption and an arbitrary extent of optical nonlinearity. The calculation technique can be used for large sample thickness too, by dividing it into thin slices. It was found that inside one slice, the distribution of the light-induced refraction is similar to that for the case of graded index media. The propagation can be described through the transformation of the q-parameter. It is demonstrated that the Z-scan technique makes the sensitive measurement of the linear absorption coefficient possible. The linear and nonlinear absorption coefficients were experimentally determined for Mg doped LiNbO3 to be =0.6 m-1 and =2.9×10-9 m/W, respectively. PACS 42.79.Ry; 78.20.Nv; 77.84.Dy 相似文献
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We have achieved efficient simultaneous intracavity doubling of the signal frequency and sum-frequency generation between the signal and the pump in a periodically poled LiNbO(3) femtosecond optical parametric oscillator pumped by a Ti:sapphire laser. The responsible mechanisms are second-, third-, and fourth-order quasi-phase matching (QPM). An ~56% poling duty cycle permits efficient even-order QPM. Femtosecond pulses tunable in the visible were generated with a total efficiency of more than 8% for only 480-mW pump power at 80 MHz. Optimization of the poling duty cycle can improve the efficiency further. 相似文献
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J. Hebling J. Klebniczki P. Heszler Zs. Bor B. Rácz 《Applied physics. B, Lasers and optics》1989,48(5):401-403
A new experimental realisation of the travelling-wave amplified spontaneous emission (TWASE) is described utilising a prismatic arrangement to get the pulse front delay in the pump beam. Rhodamine dye solutions were pumped by the amplified 25 ps long 555 nm pulses of a distributed feedback dye laser. The pulse shortening in the TWASE resulted in 12 ps output pulses with 18% energy efficiency. The observed spectrum showed numerous lines, and it contained the amplified Raman line of the pump beam. Several spots were found in the far-field zone of the generated TWASE. 相似文献
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The properties of passive Q-switched short-cavity dye lasers (SCDL) and passive Q-switched distributed-feedback dye lasers (DFDL) are investigated theoretically by using rate-equation models. The calculations, in agreement with experimental results, predict a significant decrease of the pulse energy fluctuation and the pulse duration of both the SCDL and DFDL, when passive Q-switching is used. 相似文献
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We report on efficient THz pulse generation via optical rectification with femtosecond laser pulses focused to a line by a cylindrical lens. This configuration provides phase-matched conditions in the superluminal regime. 35 pJ THz pulses have been generated with this technique in a stoichiometric LiNbO3 crystal pumped by 2 μJ femtosecond laser pulses at room temperature. An unusual superquadratic rise of the THz pulse energy with the laser pulse energy has been observed at high laser energies. This extraordinary energy dependence of the THz generation efficiency is explained by self-focusing of the laser beam in the crystal. Z-scan measurements and comparison of the THz pulse spectra created with laser pulses having different energies confirm this interpretation. 相似文献
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J. Hebling 《Applied physics. B, Lasers and optics》1988,47(3):267-272
The behaviour of an excimer-laser-pumped distributed feedback dye laser (ELP DFDL) using a mixture of saturable absorber and laser dye as an active medium was studied. In a DFDL self-Q-switching occurs because of the population inversion dependence of the feedback. If the DFDL contains absorber saturation of the absorption by the leading edge of the created laser pulse also causes Q-switching. As a result of this double self-Q-switching, mixing a saturable absorber into the laser dye, the laser pulses become shorter and more stable. This was demonstrated experimentally. Mixing Rhodamine B into the dye solution of a Coumarin 153 ELP DFDL, a six-fold reduction in the pulse duration and a more than two-fold reduction in the pulse energy instability were observed. The experimental results were in good qualitative agreement with the predictions of a simple rate equation model. 相似文献
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C. F. Oliveira F. G. Basso E. C. Lins C. Kurachi J. Hebling V. S. Bagnato C. A. de Souza Costa 《Laser Physics》2010,20(7):1659-1666
Studies have shown that the increase of cell metabolism depends on the low level laser therapy (LLLT) parameters used to irradiate
the cells. However, the optimal laser dose to up-regulate pulp cell activity remains unknown. Consequently, the aim of this
study was to evaluate the metabolic response of odontoblast-like cells (MDPC-23) exposed to different LLLT doses. Cells at
20000 cells/cm2 were seeded in 24-well plates using plain culture medium (DMEM) and were incubated in a humidified incubator with 5% CO2 at 37°C. After 24 h, the culture medium was replaced by fresh DMEM supplemented with 5% (stress by nutritional deficit) or
10% fetal bovine serum (FBS). The cells were exposed to different laser doses from a near infrared diode laser prototype designed
to provide a uniform irradiation of the wells. The experimental groups were: G1: 1.5 J/cm2 + 5% FBS; G2: 1.5 J/cm2 + 10% FBS; G3: 5 J/cm2 + 5% FBS; G4: 5 J/cm2 + 10% FBS; G5: 19 J/cm2 + 5% FBS; G6: 19 J/cm2 + 10% FBS. LLLT was performed in 3 consecutive irradiation cycles with a 24-hour interval. Non-irradiated cells cultured
in DMEM supplemented with either 5 or 10% FBS served as control groups. The analysis of the metabolic response was performed
by the MTT assay 3 h after the last irradiation. G1 presented an increase in SDH enzyme activity and differed significantly
(Mann-Whitney test, p < 0.05) from the other groups. Analysis by scanning electron microscopy showed normal cell morphology in all groups. Under
the tested conditions, LLLT stimulated the metabolic activity of MDPC-23 cultured in DMEM supplemented with 5% FBS and exposed
to a laser dose of 1.5 J/cm2. These findings are relevant for further studies on the action of near infrared lasers on cells with odontoblast phenotype. 相似文献
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Chung MK Hebling CM Jorgenson JW Severin K Lee SJ Gagné MR 《Journal of the American Chemical Society》2008,130(35):11819-11827
A dynamic combinatorial library composed of racemic hydrazone-based dipeptides becomes deracemized on binding to the chiral analytes (-)-cytidine and (-)-2-thiocytidine through the amplification of two receptors, (SS)-dimer and (RRRR)-tetramer. The deracemization phenomenon was investigated by laser polarimetry, mass-tagged pseudo-enantiomers in conjunction with electrospray ionization mass spectrometry, HPLC/UV-MS, UPLC/UV-MS, rapid-resolution LC-MS, collision-induced dissociation MS/MS, and numerical simulations. These data were consistent with a phenomenon where (SS)-dimer and (RRRR)-tetramer selectively bind the chiral analyte in preference to their enantiomeric counterparts, which ultimately causes them to be amplified and the library to become deracemized. 相似文献