Absorption spectra and light penetration depth of normal and pathologically altered human skin

A three-layered skin model (stratum corneum, epidermis, and dermis) and engineering formulas for radiative transfer theory are used to study absorption spectra and light penetration depths of normal and pathologically altered skin. The formulas include small-angle and asymptotic approximations and a layer-addition method. These characteristics are calculated for wavelengths used for low-intensity laser therapy. We examined several pathologies such as vitiligo, edema, erythematosus lupus, and subcutaneous wound, for which the bulk concentrations of melanin and blood vessels or tissue structure (for subcutaneous wound) change compared with normal skin. The penetration depth spectrum is very similar to the inverted blood absorption spectrum. In other words, the depth is minimal at blood absorption maxima. The calculated absorption spectra enable the power and irradiation wavelength providing the required light effect to be selected. Relationships between the penetration depth and the diffuse reflectance coefficient of skin (unambiguously expressed through the absorption coefficient) are analyzed at different wavelengths. This makes it possible to find relationships between the light fields inside and outside the tissue. __________ Translated from Zhurnal Prikladnoi Spektroskopii Vol. 74, No. 3, pp. 387–394, May–June, 2007.     

Light scattering by dielectric bodies of irregular shape in a layered medium in problems of biomedical optics: II. Numerical analysis

Using the mathematical model constructed earlier, optical characteristics (refractive index and absorption coefficient) of the biotissue being simulated, probed in vivo by a laser beam, are analyzed. The action spectra of the laser radiation power absorbed by oxihemoglobin and deoxihemoglobin of blood, which are associated with selectivity of absorption of radiation by these hemoglobin derivatives, are calculated.     

Theoretical studies on the structural, electronic, and optical properties of Cu2CdGeSe4

We investigate the electronic structure for Cu₂CdGeSe₄ in stannite structure with the first-principles method. This crystal is the direct band gap compound. In addition, the dielectric function, absorption coefficient, reflectivity, and energy-loss function are studied using the density functional theory within the generalized gradient approximation. We discuss the optical transitions between the valence bands and the conduction bands in the spectra of the imaginary part of the dielectric function at length. We also find a very high absorption coefficient and wide absorption spectrum for this material. The prominent structures in the spectra of reflectivity and energy-loss function are discussed in detail.     

Noninvasive determination of absorption coefficient and reduced scattering coefficient of human skin tissues in vivo with oblique-incidence reflectometry

A spatial distribution of diffuse reflectance produced by obliquely incident light is not centered about the point of light entry. The value of shift in the center of diffuse reflectance is directly related to the absorption coefficient μa and the effective attenuation coefficient μeff. μa and the reduced scattering coefficient μ's of human skin tissues in vivo are measured by oblique-incidence reflectometry based on the two-source diffuse theory model. For ten Chinese volunteers aged 15-63 years, μa and μ's are noninvasively determined to be 0.029 - 0.075 and 0.52 - 0.97 mm-1, respectively.     

Improvement of the parametric method of the theory of vibronic spectra of polyatomic molecules: Absorption spectra and the structure of butadiene, hexatriene, and octatetraene in the excited state

The structure of the excited states and absorption spectra of butadiene, hexatriene, and octatetraene are calculated by the parametric method of the theory of vibronic spectra using models of the first-and second-order approximations. It is shown that these molecular models adequately reflect the molecular structure and allow one to predict quantitatively the shape and fine vibrational structure of the absorption spectra. When passing to the second-order approximation, only two additional (angular) parameters are used. These parameters are transferable in the series of polyenes. Compared to the first-order approximation model, the second-order approximation model more accurately takes into account the angular deformations of polyenes upon their excitation and describes the intensity distribution in the vibrational spectrum, including weak lines. In addition, the calculations also quantitatively predict spectral variations in the molecular series. The parametric method is more efficient for modeling polyatomic molecules in the excited states and their vibrational spectra compared to other semiempirical and ab initio methods.     

Effect of storage conditions of skin samples on their optical characteristics

The optical characteristics of skin samples are experimentally studied ex vivo and in vitro at different storage conditions. The experiments are performed on a Cary-2415 spectrophotometer in the spectral range 400–700 nm. Based on the measured diffuse reflectance and total transmittance spectra, the spectra of the absorption and reduced scattering coefficients are calculated in terms of the inverse adding-doubling method. It is shown that the method of storage of samples mainly affects the reduced scattering coefficient of biotissue. Thus, upon storage of skin in an isotonic solution and in its absence, the reduced scattering coefficient increases ∼1.5 and ∼2 times, respectively, compared to the value of this parameter for the intact sample. The differences in the absorption spectra of ex vivo samples and samples stored under different conditions are the most noticeable in the absorption range of blood and are significant above 600 nm.     

Estimation of the spectral absorption of light by components of human skin

The spectra of the absorption coefficients of external radiation by basic chromophores of human skin, such as melanin, basic tissue, and blood (including oxy- and deoxyhemoglobin), are studied in the wavelength range of 300–1000 nm. For estimates, analytical methods of the theory of light transfer are used, which take into account the multilayer structure of a biological tissue, multiple light scattering in a medium, and multiple rereflections of radiation between layers. The calculated spectra are compared with the wavelength dependences of the absorption indices of these components available from the literature. It is shown that the spectral behaviors of the coefficients and indices of absorption strongly differ, which is related to the selectivity of the optical properties of a biological tissue. The possibilities of predicting the absorption coefficients of the skin components from the absorption coefficient of the entire skin measured under conditions of variation of its biophysical parameters (the volume concentrations of melanin and blood vessels) over a wide range are evaluated.     

The effect of an external mechanical compression on in vivo optical properties of human skin

We have studied the influence of an external mechanical compression on diffuse reflection spectra of skin tissue under in vivo conditions. An analysis of these spectra based on the diffusion approximation of the radiation transfer theory has allowed us to find that the application of the external compression weakens absorbing and scattering properties of skin tissue. After the removal of the compression, the recovery time of the skin tissue (on the order of 1 h) considerably exceeds the stabilization time of its parameters after application of external mechanical compression (several minutes). In this case, at the initial moment of time after the removal of the compression, the fullness of blood vessels and the degree of oxygenation of blood hemoglobin in the skin tissue increase considerably compared to normal skin.     

人体皮肤吸收光谱的活体检测

以Kubelka-Munk理论为基础,研究黄种人皮肤的光学特性.通过分析皮肤内的光传输模型,得出皮肤光吸收比公式,并提出一种新的基于虚拟仪器和光谱技术的皮肤光吸收作用活检方法,实现皮肤吸收光谱的活体检测,首次得到正常人体活体皮肤的吸收光谱.     

Impurity optical absorption in parabolic quantum well

Optical absorption in GaAs parabolic quantum well in the presence of hydrogenic impurity is considered. The absorption coefficient associated with the transitions between the upper valence subband and donor ground state is calculated. The impurity ground state wave function and energy are obtained using the variational method. Dependence of the absorption spectra on impurity position in quantum well was investigated. It is shown, that along with quantum well width decrease the absorption threshold shifts to higher frequencies. Results obtained within frames of parabolic approximation are compared with results for rectangular infinite-barrier quantum well case. The acceptor state → conduction band transitions considered as well.     

Sound decay in a rectangular room with impedance walls

The problem of sound decay in a rectangular room is considered for the case of a room with walls the acoustic properties of which are described by the impedance, which implies a dependence of the absorption coefficient on the angle of incidence of sound waves. The ray approximation is used to determine the sound decay laws for different distributions of wall absorption. It is shown that, in a room with impedance walls, the sound decay is slower than in the conventional reverberation model, in which the wall absorption coefficient is independent of the angle of incidence. The problem is also solved in the wave approximation to determine the decay law for a preset frequency band.     

Theoretical studies on the structural, electronic, and optical properties of Ag2HgSnSe4

We investigate the electronic structure of Ag₂HgSnSe₄ in a wurtzite-stannite structure with the first principles method. This crystal is a direct band-gap compound. In addition the dielectric function, absorption coefficient, reflectivity, and energy-loss function are studied using the density functional theory in the generalized gradient approximation. We discuss the optical transitions between the valence bands and the conduction bands in the spectrum of the imaginary part of the dielectric function at length. We also find a very high absorption coefficient and a wide absorption band for this material. The prominent structures in the spectra of reflectivity and the energy-loss function are discussed in detail.     

Spectral characteristics of indocyanine Green upon its interaction with biological tissues

The changes in the absorption spectra of solutions of Indocyanine Green are studied in relation to the nature and composition of the solvent and the dye concentration. The reflection spectra from selected areas of human skin stained with different solutions of Indocyanine Green are studied in vivo upon successive stripping of stained surface epidermal layers. The reflection spectra from human hairs stained in vitro with an alcohol solution of Indocyanine Green are measured. It is shown that the shift of the absorption band maximum of Indocyanine Green determined by the interaction of the dye with epidermal or hair keratin does not depend on the solvent composition or the depth of location of the stained layer.     

基于有效衰减系数直接测量的人体光谱特征分析

在活体成分无创测量中,人体组织的漫射光谱之间存在千差万别,即使同一组织的光谱也时刻发生着变化,这是影响活体组织成分测量精度的重要原因。通过漫射光谱实时监测组织的光学特性非常重要。由于漫射光的吸光度光谱沿光源-探测器距离不再呈现线性变化,不同距离下的测量结果不易相互借鉴,因此不宜采用单一距离的漫反射光测量方式。采用双光源-探测器距离的测量方式,通过差分测量获得了组织有效衰减系数,其与测量距离无关,是反映组织吸收、散射的综合光学参数。实验系统采用中心光纤入射,距中心0.6和2.0 mm的两个环状分布的光纤束接收漫反射光,并据此推测出被测组织的有效衰减系数。通过实时监测组织的有效衰减系数,可以监测组织的状态与成分变化信息。采用Intralipid脂肪乳作为组织仿体,考察了其中的葡萄糖浓度、血红蛋白浓度、颗粒密度、温度四个因素变化时在1 000~1 300 nm波段的有效衰减系数光谱,比较了它们的光谱特征。结果表明,有效衰减系数的光谱形状主要由介质的吸收变化决定。其中血红蛋白的有效衰减系数光谱显示出其在1 000~1 200 nm波段吸收显著,1 200~1 300 nm吸收减弱,这与血红蛋白的吸收特征一致;温度的光谱显示出与温度对水吸收光谱影响的光谱形状一致; 葡萄糖与颗粒密度引起的有效衰减系数光谱相似,原因在1 000~1 300 nm波段葡萄糖吸收较弱,其主要影响介质散射特性。最后测量了不同人体的手指、手掌、手背、手臂外侧、手臂内侧的有效衰减系数光谱,比较了部位差异和个体差异。从人体光谱差异上很明显地看到了血红蛋白、散射特性不同引起的光谱差异。综上,提出的有效衰减系数光谱测量方法特别适用于活体组织的成分测量,为实时监测组织的散射、吸收变化提供了一条新途径。     

Transmission and absorption based photoacoustic methods of determination of the optical absorption spectra of Si samples — Comparison

This paper is a comparison of two photoacoustic methods of determination of the optical absorption coefficient spectra of semiconductors illustrated with results obtained from Si samples. It presents experimental transmission and absorption photoacoustic spectra of Si samples as also the appropriate models leading to the determination of optical absorption coefficient spectra. The idea and the experimental set-up of the analyzed methods are presented in the paper too. From the fitting procedure of theoretical characteristics to experimental transmission and absorption photoacoustic spectra and after computations of the optical absorption coefficient spectra three components of the optical absorption coefficient spectra of Si samples were identified i.e. band to band transitions, Urbach tail and free carrier absorption. Their parameters are given and discussed in the paper. At the end the advantages and disadvantages of both methods are discussed. To the best of our knowledge, no such proof of the correctness of the PA method of determination of optical absorption spectra has been done.     

Effect of a finite conduction-band width on XMCD spectra at the L2,3 absorption edges of mixed-valence Ce and Yb compounds in high magnetic fields

Effect of a finite conduction-band width is studied in detail on the spectra of X-ray absorption spectroscopy (XAS) and its X-ray magnetic circular dichroism (XMCD) at the L_2,3 absorption edges of mixed valence Ce and Yb compounds in high magnetic fields. Calculations are made with an extended single impurity Anderson model and within the leading term approximation in the 1/N_f expansion method, where N_f is the degeneracy of the 4f states. It is shown that a model with a vanishing conduction-band width is applicable, as an approximation method, to the calculation of XAS and XMCD spectra for realistic systems with a finite conduction-band width, if the values of the 4f level and the hybridization strength are renormalized appropriately. This justifies the previous calculations on general features of high-magnetic-field XAS and XMCD spectra with zero conduction-band width. At the same time, it is also shown that for more realistic calculations of high-magnetic-field XMCD spectra of some specific mixed-valence Ce and Yb compounds, the present theory with a finite conduction-band width is more appropriate.     

Infrared absorption in dense sodium vapor

The absorption spectra of a dense resonance medium were experimentally studied for the example of thermally heated dense sodium vapor. Several mechanisms that might cause substantial absorption and enhanced intensity of emission in the IR spectral region, λ τ; 0.9 μm, were considered. For the first time, a detailed study of the structure of the absorption spectra of sodium vapor in the specified wavelength range was performed to determine the influence of the kind and pressure of the buffer gas. It was found that buffer gas characteristics had a substantial effect on the absorption coefficient of vapor. The presence of the molecular component (dimers and trimers) in sodium vapor could not explain the experimental dependences of absorption in the infrared region. Possible influence of microparticles formed in condensation of convective sodium vapor flows in heated cells on the optical properties of vapor was considered. Microparticles could contribute to the observed absorption, but were incapable of explaining the substantial intensity of vapor radiation reported earlier. Possible many-particle effects on the absorption in the far spectral line wing were discussed. For the first time, the method of molecular dynamics was used to show for the example of the distribution function of ionic microfields in a dense plasma that such effects were in principle capable of substantially raising the profile of the line and increasing absorption in the region of large detunings from the resonance compared with the simple quasi-static model in the nearest-neighbor approximation.     

Energy spectrum and optical absorption spectra of carbon nanotubes with chiralities of (10, 10), (11, 9), and (12, 8)

The energy spectra of single-wall carbon nanotubes (CNTs) with chiralities of (10, 10), (11, 9), and (12, 8) are calculated in the static fluctuation approximation for the Hubbard model. The choice of these systems for investigation was dictated by the fact that these systems are the most typical of heterogeneous samples obtained by synthesis. It is shown that in the chosen model and approximation, the type of conduction is independent of chirality, which contradicts the generally accepted opinion concerning the critical dependence of the CNT conduction current on the chirality indices. The optical absorption spectra of the CNTs under investigation are calculated using the resultant energy spectra. The shape of the optical absorption spectrum averaged over the known weight composition is in good agreement with experimental data. The results of investigation suggest that the rule according to which CNTs exhibit metal-type conductivity when the difference in the chirality indices is a multiple of three; otherwise, they have the semiconductor-type conductivity, is in all probability not general, but has applicability limits that can be established by rigorous calculations based on the Hubbard model.     

呋喃妥因的太赫兹光谱分析

利用太赫兹时域光谱技术测量了硝基呋喃类药物中呋喃妥因原药在0.2～1.8 THz范围内的吸收系数、折射率等光学指纹特性,结果表明呋喃妥因在该频率范围内出现了多个强度不同的特征吸收峰,吸收系数光谱可用于鉴定呋喃妥因。借助Gaussian软件利用密度泛函理论对呋喃妥因分子在0.2～1.8 THz范围内的吸收系数光谱进行了模拟,并对吸收系数实验光谱中部分吸收峰的振动模式进行了分析和指认。结果表明实验谱中1.25和1.60 THz处的吸收峰与理论谱中1.30和1.67 THz处吸收峰一致,是由呋喃妥因分子内的振动模式引起的。     

Optical transitions in spherical quantized layer under the presence of radial electrical field

Single electronic states and direct optical transitions in the quantized spherical layer under the presence of static radial electric field are considered. In dipole approximation, the electrooptical absorption coefficient for interband and inband–intersubband direct transitions are calculated. The selection rules and explicit dependence of absorption coefficient from the field factor and geometrical sizes of the model are revealed.