DEPTH OF FIELD The working range of the beam in or near the focal plane of
a lens; a function of wavelength, diameter of the unfocused beam, and focal length
of the lens.
DEPTH OF FOCUS The distance over which the focused laser spot has a constant
diameter and thus constant irradiance.
DICHROIC FILTER Filter that allows selective transmission of colors desired
wavelengths.
DIFFRACTION Deviation of part of a beam, determined by the wave nature of radiation
and occurring when the radiation passes the edge of an opaque obstacle.
DIFFUSE REFLECTION Takes place when different parts of a beam incident on a
surface are reflected over a wide range of angles in accordance with Lambert's
Law. The intensity will fall-off as the inverse of the square of the distance
away from the surface and also obey a Cosine Law of reflection.
DIFFUSER An optical device or material that homogenizes the output of light
causing a very smooth, scattered, even distribution over the area affected. The
intensity will obey Lambert's law (see Diffuse Reflection).
DIVERGENCE The increase in the diameter of the laser beam with distance from
the exit aperture. The value gives the full angle at the point where the laser
radiant exposure or irradiance is e(-1) or e(-2) of the maximum value, depending
upon which criteria is used.
DOSIMETRY Measurement of the power, energy, irradiance or radiant exposure
of light delivered are two crystalline materials used as laser to tissue.
DRIFT All undesirable variations in output either amplitude or frequency).
ANGULAR DRIFT Any unintended change in direction of the beam before, during,
and after warmup; measured in mrad.
DUTY CYCLE Ratio of total "on" duration to total exposure duration for a repetitively
pulsed laser.
