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Optoacoustic imaging:Thermoelastic expansionSteven L. Jacques, Guenther Paltauf |
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Optoacoustic imaging:Thermoelastic expansionSteven L. Jacques, Guenther Paltauf |
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The pressure generated in an object by thermoelastic expansion due to a very short laser pulse is described:
| where | M | = Bulk Modulus [Pa/strain], strain is dimensionless |
| = rho cs2, rho = density [kg/m3], cs = sound velocity [m/s] | ||
| beta | = Thermal expansivity [strain/degreeC], strain is dimensionless | |
| rho | = Density [kg/m3] | |
| Cp | = Specific heat [(J/(kg degC)] | |
| Gamma | = Grueneisen coefficient [dimensionless] | |
| mua | = Absorption coefficient [m-1] | |
| H | = Radiant exposure [J/m2] | |
| W | = Energy depostion [J/m3] |
The energy deposition W = (mua)(H) [J/m3].
The temperature rise = (energy deposition)/(rho Cp) [degree C].
The strain = (beta)(temperature rise) [dimensionless].
The stress or pressure = (M)(strain) [J/m3] = [kg/(m s2] = [Pa].
The Grueneisen coefficient Gamma = (M)(beta)/(rho Cp) [dimensionless].
The units of pressure (P) are (force)/(area). The units of energy deposition (W) are (energy)/(volume) = (force x distance)/(area x distance) in which the distance term cancels to equal (force)/(area). Hence the units of pressure and energy deposition are identical. The conversion factor for pressure is 1 J/m3 = 1 Pa = 10-5 [bar].
