OBT Principles of Optical Beam Physics 3

Question 1

What is the primary advantage of using pulsed over continuous-wave (CW) optical beams in some therapeutic applications?

Accepted Answer

Selective thermal confinement via thermal relaxation time

Answer

Pulsed delivery allows the pulse duration to be shorter than the thermal relaxation time of the target, confining heat and minimizing collateral damage.

Question 2

In optical beam physics, what does the term 'coherence length' refer to?

Accepted Answer

The propagation distance over which a beam maintains phase correlation

Answer

Coherence length is the propagation distance over which a light wave maintains a specified degree of phase coherence, important for interference-based techniques.

Question 3

Which scattering type dominates in biological tissue for visible and near-infrared wavelengths?

Accepted Answer

Mie scattering

Answer

Mie scattering dominates in tissue because cellular structures (nuclei, organelles) are comparable in size to the wavelengths used in therapy.

Question 4

What is the 'optical window' in biological tissue, and why is it therapeutically significant?

Accepted Answer

600–1100 nm range where absorption by water and hemoglobin is minimized, allowing deeper penetration

Answer

The optical window (600–1100 nm) is where tissue chromophores absorb least, enabling deeper light penetration for therapeutic applications.

Question 5

How does increasing the numerical aperture (NA) of an optical delivery system affect the focused spot size?

Accepted Answer

Decreases spot size

Answer

Higher NA captures a larger cone of light, enabling tighter focusing and a smaller diffraction-limited spot size (d ≈ λ/2NA).

(OBT) Optical Beam Therapy Certification Practice Test

(OBT) Optical Beam Therapy Certification Practice Test

OBT Principles of Optical Beam Physics 3