No standard comprehensive nomenclature or notation is currently generally adapted in the field of laser tissue interaction. Part of the reason for this is the conflict of standard notation when merging the fields of optics and heat transfer which leads to duplication of many symbols. Welch and van Gemert have proposed a standard set of notations in their book 'Optical-Thermal Response of Laser Irradiated Tissue', which are to a large extent based on the ISO Standards on Quantities and Units of Light and Related Electromagnetic Radiation. We will use this proposed notation convention. A summary of important and often used symbols is given below.
Basic Parameters
| SYMBOL | DESCRIPTION | DEFINITION | UNITS |
| A | Area | m2 | |
| t | Time | s | |
| V | Volume | m3 | |
| r,z | position | (x,y,z) |
Optical Parameters
| SYMBOL | DESCRIPTION | DEFINITION | UNITS |
| R | Reflectance | ||
| T | Transmission | ||
| d | Penetration depth of collimated light | d = 1/m t | m |
| ma | Absorption coefficient | Probability of absorption per infinitesimal path length | 1/m |
| ms | Scattering coefficient | Probability of scattering per infinitesimal path length | 1/m |
| mt | Total attenuation coefficient |
Probability of interaction per infinitesimal path length mt = ma + ms |
1/m |
| g | Anisotropy factor | Average cosine of angle of scattering | |
| ms ’ | Reduced scattering coefficient | ms ’ = ms (1-g) | 1/m |
Light Parameters
| SYMBOL | DESCRIPTION | DEFINITION | UNITS |
| l | wavelength | m | |
| n | frequency | 1/s | |
| Eo, E | Irradiance at surface | W/m2 | |
| H | Radiant exposure | H=ò E dt | J/m2 |
| Q | Radiant energy | Q=hnN | J |
| W | Radiant energy density | W=DQ/DV | J/m3 |
| f | Fluence rate | W/m2 | |
| y | Fluence | y=ò f dt | J/m2 |
| tp | Pulse duration | s | |
| ¦ | Repetition rate or pulse frequency | Number of pulses per unit time | 1/s |
| wL | Spot radius | Assume Gaussian | m |
| Qp | Laser pulse energy | J | |
| n | Index of refraction |
Thermal Parameters
| SYMBOL | DESCRIPTION | DEFINITION | UNITS |
| T | Temperature | °C,K | |
| c | Specific heat | J/kg°C | |
| k | Thermal conductivity | W/m°C | |
| Lv | Latent heat of vaporization | J/kg | |
| r | Density | Kg/m3 | |
| a | Thermal diffusivity | a=k/(rc) | m2/s |
| S | Rate of heat generation | S=maf | W/m3 |
| P | Pressure | Bars | |
| t | Thermal diffusion time | S | |
| W | Volume expansion factor | ||
| C | Concentration | mol/l | |
| A | Frequency factor or molecular collision rate | 1/s | |
| Ea | Activation energy | J/mol | |
| R | Universal gas constant | J/mol K | |
| W | Damage integral |
Useful Constants
| SYMBOL | DESCRIPTION | DEFINITION | UNITS |
| h | Planck's Constant | 6.62 10-34 | J s |
| R | Universal Gas Constant | 8.234 | J/mol K |
| r | Density of water at 20 oC and 1 atm | 1.0 103 | kg/m3 |
| c | Heat capacity of water at 20 oC and 1 atm | 4.18 103 | J/kg K |
| Lv | Latent heat of vaporization of water at 1 atm | 2,260 | J/g |