Oscillations, Waves, and Interactions - GWDG

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220 A. Vogel, I. Apitz, V. Venugopalan well characterized by the scaling law µ ′ s ∼ λ −b where b ∼ 0.5–2 [12,13]. Optical scattering will reduce the optical penetration depth δ of light relative to the absorption depth (1/µa). In addition, when scattering is dominant over absorption, backscattering and total internal reflection lead to a fluence rate proximal to the tissue surface that can exceed by several times the incident irradiance [14,15]. However, ablation is typically performed at wavelengths where µa ≫ µ ′ s. The thermal and mechanical transients generated during the pulsed laser ablation process are substantial and can result in dynamic changes of the optical absorption properties. Motivated by spectroscopy literature indicating that the absorption peak of water at λ = 2.94 µm drops and shifts towards shorter wavelengths for increasing temperature [18], various researchers investigated the reduction in the IR absorption coefficient of tissue when heated [16,19,20]. In Fig. 3 we present data for the dependence of the absorption coefficient of water on volumetric energy ε for λ = 2.94 and 2.79 µm [16,17], and of the variation in optical penetration depth with incident radiant exposure [6]. The latter results, shown in the bottom of Fig. 3, demonstrate that for Φ0 > 0.5 J/cm 2 , Er:YSGG laser radiation (λ = 2.79 µm) offers better spatial confinement of the laser energy compared to Er:YAG laser radiation (λ = 2.94 µm). This is opposite to the behaviour one would expect from the absorption coefficients measured at small radiant exposures (Fig. 2). Variations in optical absorption with temperature are also important for ultraviolet laser ablation. Staveteig and Walsh [21] hypothesized that absorption of UV radiation by peptide bonds is followed by heating of the surrounding water that results in a change in hydrogen bonding structure of water and thus to a red shift of the water absorption band, which at room temperature is located at 160 nm. They demonstrated that the absorption of water at λ = 193 nm may be raised to as much as µa ≈ 10 4 cm −1 at ε = 2 kJ/cm 3 . Phase transitions of the tissue water are strongly influenced by the mechanical tissue properties. There is a positive correlation between tissue strength and collagen content. Tissues that represent extremes of mechanical strength are the liver and tendon. Liver is a cell-continuous tissue with little ECM and collagen content, which results in a very low ultimate tensile strength (UTS) of 23 kPa and moderate extensibility at fracture ∼ 50% [9,22]. Tendon is a matrix-continuous tissue that possesses high collagen content. This provides for high strength and stiffness with an UTS of � 100 MPa and fracture extensibility of ∼ 10%. Skin has similarly high collagen content (25–33%) but lower UTS (∼ 10 MPa) and much larger fracture extensibility of ∼ 30–100% because the collagen fibrils in the dermis are “wavy” and form a loose three-dimensional network [9] (see Fig. 1). Nearly all tissue mechanical data have been acquired under “quasi-static” loading conditions in which the tissue is deformed at very slow strain rates; typically on the order of 10 −3 s −1 . However, the processes involved in pulsed laser ablation of tissue produce extremely high strain rates; on the order of 10 5 –10 7 s −1 . Studies performed to examine the effect of strain rate in the range 0.3–170 s −1 have revealed that while the tissue strain at fracture remains roughly constant, the UTS increases in proportion to the logarithm of the strain rate [23–25]. The increase in UTS is due to the viscous dissipation between the collagen fibrils and the adjacent ground substance during the rapid deformation. It is not known whether the logarithmic dependence between strain rate and tissue UTS remains valid at the extreme strain
Dynamics of pulsed laser tissue ablation 221 Figure 3. Graphs illustrating the effects of dynamic optical properties of a water target produced by Er:YAG (λ = 2.94 µm) and Er:YSGG (λ = 2.79 µm) laser irradiation; top: variation of optical absorption coefficient of water with volumetric energy density. Data compiled from Refs. [16] and [17]; bottom: variation of optical penetration depth with incident radiant exposure. Optical penetration depth is defined as the location at which the volumetric energy density drops to 1/e of the surface value. Note that for incident radiant exposures F0 > 0.4 J/cm 2 , Er:YSGG laser irradiation offers more superficial energy deposition compared to Er:YAG laser irradiation. rates produced by pulsed laser ablation. However, the available UTS data suggest that the tissue strength under ablative conditions can be considerably higher than
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Thomas Kurz, Ulrich Parlitz, and Ud
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erschienen im Universitätsverlag G
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Bibliographische Information der De
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iv Contents Laser speckle metrology
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Oscillations, Waves and Interaction
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Applied physics at the “Dritte”
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noise component [GNE] 5 4 3 2 1 can
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3.4 Transfer to running speech Spee
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3.4.2 Analysis of running speech Sp
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Speech research 33 Area [Pixels] 60
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Speech research 35 [13] D. Michaeli
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Specific signal types in hearing re
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74 D. Ronneberger et al. Mechel fou
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76 D. Ronneberger et al. (flow velo
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78 D. Ronneberger et al. |t + acous
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80 D. Ronneberger et al. Figure 6.
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82 D. Ronneberger et al. Figure 8.
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84 D. Ronneberger et al. (flow velo
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86 D. Ronneberger et al. R / L ⋅
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88 D. Ronneberger et al. e. g. temp
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90 D. Ronneberger et al. 3.2 Qualit
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92 D. Ronneberger et al. As usual t
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94 D. Ronneberger et al. (wavenumbe
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96 D. Ronneberger et al. powers of
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98 D. Ronneberger et al. an increas
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100 D. Ronneberger et al. The term
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102 D. Ronneberger et al. Neverthel
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104 D. Ronneberger et al. [4] J. Br
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106 D. Ronneberger et al. strömung
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108 D. Guicking synchronised tuning
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110 D. Guicking primary noise micro
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112 D. Guicking primary sensor desi
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114 D. Guicking by an antiphase sou
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116 D. Guicking R L C C + + 1 1−C
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118 D. Guicking More involved than
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120 D. Guicking In the 1980s, longi
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122 D. Guicking with electrodynamic
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124 D. Guicking 3.6 Noise reduction
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126 D. Guicking the turbulence of a
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128 D. Guicking References [1] Lord
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130 D. Guicking [44] Falcke, H.,
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132 D. Guicking [84] J. Melcher,
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134 D. Guicking [125] D. Heyland et
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136 D. Guicking [166] S. Zommer et
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138 D. Guicking [212] M. L. Post an
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140 W. Lauterborn et al. liquid κ
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142 W. Lauterborn et al. Figure 2.
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144 W. Lauterborn et al. nator, and
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146 W. Lauterborn et al. by types a
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148 W. Lauterborn et al. bubble rad
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154 W. Lauterborn et al. P koll [kb
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156 W. Lauterborn et al. Pulse widt
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158 W. Lauterborn et al. laser puls
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168 W. Lauterborn et al. R [µ m] 1
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270 K. D. Hinsch Figure 7. Optical
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272 K. D. Hinsch Figure 9. Humidity
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274 K. D. Hinsch locations that tak
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276 K. D. Hinsch Figure 13. Map of
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278 K. D. Hinsch References [1] D.
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280 Schreiber not moving along with
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282 Schreiber These properties made
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284 Schreiber Figure 3. The G ring
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286 Schreiber Rotation Rate [rad/s]
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288 Schreiber and it is currently b
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290 Schreiber n1 D A B n Figure 8.
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292 Schreiber Beamwalk [µm] 80.0 7
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294 Schreiber ∆ Perimeter [*10e12
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296 Schreiber and the last term acc
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298 Schreiber Δf [µHz] 100 50 0 -
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300 Schreiber formation of a new wo
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302 Schreiber PSD [*10 16 (rad/s) 2
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304 Schreiber 7.2 The ring laser co
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306 Schreiber Demodulator Signal [V
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308 Schreiber Est. Phase Vel. (m/s)
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310 Schreiber [18] V. Frede and V.
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312 Martin Dressel tice is reduced
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314 Martin Dressel Metallic whisker
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316 Martin Dressel (a) (b) (c) CH 3
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318 Martin Dressel 3.1 Charge densi
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320 Martin Dressel Absorptivity σ
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322 Martin Dressel brought a confir
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324 Martin Dressel a charge disprop
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326 Martin Dressel Conductivity 70
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328 Martin Dressel Reflectivity Con
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330 Martin Dressel References [1] M
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332 Martin Dressel and L. Montgomer
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334 R. Pottel, J. Haller and U. Kaa
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368 U. Kaatze and R. Behrends with
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370 U. Kaatze and R. Behrends Figur
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386 U. Kaatze and R. Behrends of th
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398 U. Kaatze and R. Behrends [6] M
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400 U. Kaatze and R. Behrends [49]
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402 U. Kaatze and R. Behrends (2002
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404 U. Kaatze and R. Behrends Copyr
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406 U. Parlitz here chaos control m
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408 U. Parlitz Figure 2. Amplitude
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410 U. Parlitz 4 10 5 5 (a) (b) (c)
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412 U. Parlitz two-parameter studie
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414 U. Parlitz GN differential opti
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416 U. Parlitz P 1 P 2 P 3 S P 1 P
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418 U. Parlitz Figure 9. Correlatio
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420 U. Parlitz series” where for
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422 U. Parlitz current state future
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424 U. Parlitz tion [69] of two uni
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426 U. Parlitz LD1 LD2 M BS1 BS2 OD
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428 U. Parlitz with a clear tendenc
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430 U. Parlitz (a) y (c) y 40 20 È
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432 U. Parlitz [29] P. Grassberger,
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434 U. Parlitz [76] H. D. I. Abarba
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436 S. Lakämper and C. F. Schmidt
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462 Index basin of attraction, 144
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464 Index cone bubble structure, 19
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466 Index turbulent, 111, 126 fluct
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468 Index LPC, 29 luminescence of b
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470 Index peak factor, 38, 43 Peier
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472 Index laser-induced bubble, 152
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474 Index ultraharmonic resonance,
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