Temperature Dependence Of Absorption Coefficient Research Articles

Thermal stability and optical properties of aromatic polyimides containing side-substituted azobenzene groups

Aromatic azopolyimides based on 9,9-bis[4-(3,4-dicarboxyphenoxy)phenyl]fluorene dianhydride and aromatic diamines containing substituted azobenzene group have been studied regarding their thermal and photooptical properties. The thermal analysis showed that the decomposition of these polymers takes place in two or three stages. The optical properties of the investigated polymers have been analyzed by transmission and reflectivity measurements within the spectral range of 200–2500 nm. Temperature dependence of absorption coefficient has been found on the basis of “in situ” transmission measurements, during annealing of thin films up to 300°C. It turned out that this process did not change the conjugation of polymer chain but caused a slightly more, irreversible structural disorder.

OH in natural orthopyroxene: an in situ FTIR investigation at varying temperatures

In situ unpolarized and polarized Fourier transform infrared spectra of a natural orthopyroxene at varying temperatures were obtained using a heating stage attached on an Infrared microscope. The three main bands (3,595, 3,520 and 3,410 cm−1) at room temperature are ascribed to OH fundamental stretching bands. With increasing temperature from room temperature to 500 °C, the 3,595 cm−1 band shifts 20 cm−1 to lower frequency. The total integral absorbance decreases with increasing temperature. These changes are reversible. Excluding the influences of dehydration, proton migration, thermal expansion, and changes in OH dipole direction, the change of integral absorbance with temperature reflects the temperature dependence of absorption coefficient due to the anharmonicity of OH vibration. Based on the integral absorption coefficient at room temperature (14.84 ppm−1 cm−2) from Bell et al. (Am Mineral 80:463–474, 1995), the integral absorption coefficients at other temperatures are calculated. The variation of integral absorption coefficient between room temperature and 500 °C obtained in this study is about 18.5 % and may be greater at higher temperature according to the proposed linear relationship.

Improved thermal model and its application in UV high-power pulsed laser ablation of metal target

An improved thermal model describing UV high-power nanosecond laser ablation of metal target is presented. The vaporization effect, the plasma shielding effect, as well as the absorption coefficient and absorptivity dependence of temperature are considered in this model. Take iron target as an example, the numerical solutions are obtained from the heat flow equations (before and after melting) using a finite difference method. The space and time dependence of temperature of the target, the time dependence of temperature at two different positions for a certain laser fluence, and the ablation rate as a function of laser fluence are also presented. The numerical results that agreed well with the experimental data are much better than the one without, which indicates that the above two effects and the temperature dependence of absorption coefficient and absorptivity in UV high-power laser ablation of metal target should not be neglected. We hope the present model will be useful for further experimental investigation of metal thin films prepared by pulsed laser deposition.

Analysis of Internal Modified-Layer Formation Mechanism into Silicon Single Crystal with Nanosecond Laser

When a permeable nanosecond pulsed laser is focused into the interior of a silicon wafer and is scanned in the horizontal direction, a belt-shaped high dislocation density layer that consists of a partially polycrystalline region that is formed at an arbitrary depth in the wafer. By applying tensile stress perpendicularly to this belt-shaped modified-layer, the silicon wafer can be separated easily into individual chips without creating any damage to the wafer surface compared to the conventional blade dicing method, because the internal cracks spread from the modified layer up and down to the surfaces. This technology is called “stealth dicing” (SD), and attracts attention as a novel dicing method in semiconductor industries. The purpose of this study is to clarify the formation mechanism of modified layer. A coupling problem composed of focused laser propagation in a silicon single crystal is examined, considering laser absorption, temperature rise, and heat conduction, with particular attention to an experimental result that the absorption coefficient varies with temperature. Simple thermal stress analysis was also conducted based on those results. As a result, the formation mechanism of the modified layer could be explained clearly. It was seen that the temperature dependence of absorption coefficient is the most important factor of the modified layer formation. The present analysis can be applied to find the optimum laser irradiation condition for SD method.

Effects of the temperature dependence of absorption coefficients in edge-pumped Yb:YAG slab lasers

A study of the temperature dependence on an absorption coefficient is presented. We describe the absorption spectrum measurement of the laser material Yb:YAG that was performed over a wide temperature range. As the temperature increases from 23°C to 300°C, the central wavelength of the Yb:YAG absorption spectrum at 940 nm varies slightly from 941.2 nmto941.1 nm, and the maximal absorption cross section drops dramatically from 7.89×10−21 cm2 to 4.23×10−21 cm2. According to our experimental results, we have presented an analytic description of temperature distribution with the numerical iterative method and have investigated the pumping optimization and laser oscillator performance, taking into account that the absorption coefficient is strongly influenced by temperature. Our analyses also include the effect of pump absorption saturation and the temperature dependence of Boltzmann population fractions, stimulated emission cross section, and thermal conductivity. We have shown that the predicted laser output power exceeds the actual value if the temperature dependence of Yb:YAG's absorption coefficient is neglected.

Advanced Dicing Technology for Semiconductor Wafer—Stealth Dicing

Stealth Dicing (SD) was developed to solve such inherent problems of dicing process as debris contaminants and unnecessary thermal damage on work wafer. In SD, laser beam power of transmissible wavelength is absorbed only around focal point in the wafer by utilizing temperature dependence of absorption coefficient of the wafer. And these absorbed power forms modified layer in the wafer, which functions as the origin of separation in followed separation process. Since only the limited interior region of a wafer is processed by laser beam irradiation, damages and debris contaminants can be avoided in SD. Besides characteristics of devices will not be affected. Completely dry process of SD is another big advantage over other dicing methods.

Modified-layer formation mechanism into silicon with permeable nanosecond laser

The purpose of this study is to clarify the formation mechanism of modified layer. A coupling problem composed of focused laser propagation in a silicon single crystal is examined, considering laser absorption, temperature rise and heat conduction, with particular attention to an experimental result that the absorption coefficient varies with temperature. Simple thermal stress analysis was also conducted based on those results. As a result, the formation mechanism of the modified layer could be explained clearly. It was seen that the temperature dependence of absorption coefficient is the most important factor of the modified layer formation. This present analysis can be applied to find the optimum laser irradiation condition for Stealth Dicing (SD) method, and it is a future subject to confirm it experimentally. It was supported by this present analysis that the problem of thermal effect on the device region can be solved by the SD method. [Received 7 May 2006; Accepted 2 February 2007]

Thermo-Elastic-Plastic Analysis on Internal Processing Phenomena of Single-Crystal Silicon by Nanosecond Laser

When a nanosecond pulse laser is irradiated into a single crystal silicon, a local area near the focal point is melted and solidified, and internal cracks develop from this modified layer to the surrounding single crystal layer. This processing is applied to a dicing of silicon wafer, which is called stealth dicing (SD) and attracts attention in industries of semiconductor. A light of 1064 nm penetrates usually through a single crystal silicon. When a pulsed laser of this wavelength with high pulse energy is focused up to near the diffraction limit inside the silicon, however, strong absorption occurs near the focal point. This phenomenon depends on not only increase of beam intensity by focusing but also the temperature dependence of absorption coefficient. We conducted the thermo- elastic-plastic analysis by the finite element method, and calculated the stress intensity factor. As a result, the stress intensity factor exceeds the fracture toughness of a silicon. This result suggests the possibility of crack development from the modified layer to the surrounding single crystal layer.

428 透過性ナノ秒レーザによるシリコンの内部改質層形成機構(OS-14 レーザ応用加工)

When a permeable nanosecond pulse laser which is focused into the inside of a silicon wafer is scanned in the horizontal direction, a belt-shaped high dislocation density layer is formed at an arbitrary depth in the wafer. Applying tensile stress perpendicularly to this belt-shaped modified layer, silicon wafer can be separated easily into individual chip without creating any damage to the wafer surface comparing with the conventional blade dicing method, because the cracks that spread from the modified layer up and down progress to the surface. This technology is called "stealth dicing" (SD), and attracts attentions as a novel dicing technology in semiconductor industries. In order to clarify the formation mechanism of modified layer, we paid attention to an experimental result that the absorption coefficient varies with temperature. We analyzed a coupling problem composed of focused laser propagation in a silicon single crystal, laser absorption, temperature rise, and heat conduction. Simple thermal stress analysis was also conducted based on those results. As a result, formation mechanism of the modified layer could be explained clearly. Temperature dependence of absorption coefficient is the most important factor of the modified layer formation.

Mathematical model and some nonlinear effects of heat and mass transfer in multiphase media under action of high-frequency electromagnetic radiation

The application of high-frequency electromagnetic radiation is one of the promisingmethods inoilandgas technologies,that canbewell usefor struggleagainst pitch, paraffin or gas-hydrate fall-out in wells and in pipelines, for action on reservoir and for other purposes. During in the operation of wells on their surfaces the asphalt-pitch-paraffinfall-out areoccurs causedof lowingof temperatureandpressure. These fall-out fills the space between pipes, that bring to a stop of well sometimes. The high-frequency electromagnetic heating is convenient mean (and the only possible way in some cases) to eliminate these complications. By that the experiments and the numerical simulation shows, that some nonlinear effects are possible. These effects are caused due to some media have temperature dependence of absorption coefficient. This dependence can be have more or less expressed “resonance“ view, to say have maximum by certain temperature. The position, height and width of that ”resonance“ dependences of electromagnetic radiation frequency and of dielectric properties of medium. These nonlinear properties can be used to rise of heating efficiency. If the radiation frequency is correct, one can to realize the heating in a ”temperature wave“ regime, that essentially rises the velocity of heating. And what is more, if one will use the nonlinear dependences α(T), one can to realize a ”reverse temperature wave“, that will move backwards: from far end of tube to the source of radiation, i.e. one can receive effects, those are impossible by usual conditions. Inthispaperthe temperaturedependence of absorption coefficient is investigated and the mathematical modelling of high-frequency electromagnetic heating (with due regard for this dependence) is carried out.

A k distribution method considering centres and wings of atmospheric absorption lines

The k distribution method is applied to band overlap and pressure as well as temperature dependence of absorption coefficients. The overlap of spectral absorption coefficients of H2O, CO2, O3, N2O, and CH4 is considered by a multivariate frequency distribution of absorption coefficients for a given pressure and temperature. In a first approach the vertical inhomogeneity is taken into account by the separation into the absorption coefficient at a reference state, the temperature dependence of the line strengths, and the dependence of the line profiles on pressure and temperature. If at distinct spectral positions absorption coefficients are changing from line wing absorption in the lower atmosphere to line centerlike absorption in the stratosphere, this is considered by a rough approximation. The known far wing scaling approximation is included, modified as special case. Comparison of infrared radiation flux densities in a standard atmosphere from this k distribution method with those from a line‐by‐line model leads to a difference about −1.8 W/m2 for the upward radiation flux density at the top of the atmosphere and −0.25 W/m2 for the downward directed at the surface. Cooling rate differences remain smaller than |0.1| K/d for the entire troposphere, but reach an intolerable 5 K/d at 50‐km height. In a second approach an extended version of the k distribution model is obtained by separating the spectral absorption coefficients into central and wing contributions. A multivariate frequency distribution which considers both strongly increases accuracy to less than 0.2% relative error for flux densities at all heights. And for cooling rates, a relative error of at most ±15% is found in the upper stratosphere.

Temperature Dependence of Absorption Coefficient in Silicon of Lower Purity

Temperature Dependence of Absorption Coefficient in Silicon of Lower Purity

Temperature dependence of the absorption coefficient of CH 2O at the 3.508 μm HeXe laser line

The observed temperature and pressure dependence (for 700⩽ T, °K⩽2100, 0.44⩽ p, atm⩽2.7) of the spectral absorption coefficient of formaldehyde at the HeXe laser line at 3.508 μm may be accounted for by assuming that the principal contribution at elevated temperatures is made by an isolated, distant line in the ground vibrational state.

溶融ZnCl<SUB>2</SUB>-MCl (M=Li, Na, K, Cs) 2成分系の超音波の吸収

Absorption coefficients of ultrasonic waves in the molten ZnCl2-MCl (M=Li, Na, K, Cs) binary systems were measured with a U.S. spectrometer by the double-transducer method over the frequency range of 5 to 55 MHz. Bulk viscosity coefficients of these systems were determined from the measured absorption data.The results obtained are summarized as follows:(1) Absorption coefficient is greatest in pure ZnCl2 and decreases with increasing content of MCl for all these systems. The absorption coefficient of pure ZnCl2 shows the greatest negative temperature gradient. The temperature dependence of absorption coefficients for the mixtures decreases with increasing MCl content and becomes constant within the experimental error in the composition range of more than 70 mol%MCl for all these systems.(2) Bulk viscosity of pure ZnCl2 has an extremely large value and a large negative dependence on temperature. For all the systems, bulk viscosity coefficients on the ZnCl2-rich side decrease markedly with increasing MCl content and the extent of decrease increases in the order of LiCl<NaCl<KCl<CsCl.(3) Composition dependences of the apparent activation energies of bulk viscosity, EηB, and the ratio of apparent activation energies of bulk and shear viscosities, EηB⁄EηS were determined. It is found that the ratio EηB⁄EηS is nearly equal to unity on the ZnCl2-rich side except the ZnCl2-CsCl system. This fact may indicate that the mechanism of bulk viscosity is analogous to that of shear viscosity on the ZnCl2-rich side.(4) Bulk viscosity coefficients of alkali metal chlorides obtained in the present work are much smaller than those reported by other investigators. Compared with the organic liquids and the calculated values by the two state model combined with the hole theory, it is suggested that the present results are more reasonable than the others.

Pressure and temperature dependence of Freon-12 absorption coefficients for CO_2 waveguide laser radiation

Freon-12 absorption coefficients for the P(22) through P(48) CO(2) waveguide laser transitions of the 00 degrees 1-(10 degrees 0, 02 degrees 0)(I) band are presented. For pressures below 10 Torr and a spectral resolution of 0.1 MHz, the absorption coefficients show considerable spectral structure within +/-250 MHz of the CO(2) laser line center; but individual absorption lines are only resolved for pressures below 100 microm. The absorption coefficients around the CO(2) waveguide laser lines are shown to be spectrally structureless as well as pressure independent above 20 Torr. The temperature dependence of the absorption coefficients are presented for the first time, and they are shown to be linearly dependent on temperature.

Refractive Indices and Absorption Coefficients of SbSBr

Refractive indices n a , n b and n c of SbSBr have been found to be 2.64, 3.13 and 4.00, respectively, using modified Chaulnes' method. These values can be explained as being caused by the large electronic polarizabilities of sulfur and bromine. Absorption coefficients for the light having electric vectors parallel to the [100], [110] and [001] were obtained. Although SbSBr is paraelectric in the measured temperature range of -60∼190°C, non-linear temperature dependence of absorption coefficients was observed. The results are discussed in comparison with those for SbSI.