Biomedical Optics 4 MCQ

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Questions and Answers

What is the primary active medium used in Nd:YAG lasers?

Carbon dioxide gas

Gallium nitride

Dye solution

Yttrium-aluminum-garnet crystal (correct)

In which clinical application is the ArF excimer laser primarily utilized?

Tumor ablation

Pain management therapy

Laser eye surgery (LASIK) (correct)

Dental procedures

What feature characterizes the laser diodes mentioned in the content?

They emit continuous waves exclusively.

They utilize a resonant cavity to form the laser. (correct)

They require cryogenic temperatures to function.

They operate only at UV wavelengths.

What is the range of power output displayed by clinical Nd:YAG lasers?

10-50W Signup and view all the answers

What is a significant property of pulsed excimer lasers?

They produce pulses of approximately 10 ns. Signup and view all the answers

Which wavelength is associated with the ArF excimer laser?

193 nm Signup and view all the answers

How is the energy emission characterized in pulsed Nd:YAG lasers?

They can generate pulses ranging from tens to several hundred mJ. Signup and view all the answers

What aspect of ArF excimer laser function allows for photoablation without thermal damage?

Short wavelength Signup and view all the answers

Which laser is known for its application in treating vascular lesions?

Pulsed dye laser Signup and view all the answers

What type of bonds are formed between the Ar and K atoms in an ArF excimer laser?

Ionic bonds Signup and view all the answers

What is a primary characteristic of the Diode laser?

Used primarily for laser hair removal Signup and view all the answers

What type of light does the Argon laser emit?

Blue-green light Signup and view all the answers

What clinical applications are associated with diode lasers mentioned in the content?

Optical imaging and photodynamic therapy Signup and view all the answers

Which laser is most suitable for skin resurfacing procedures?

Er: YAG laser Signup and view all the answers

The wavelength of the Alexandrite laser is closest to which of the following?

755 nm Signup and view all the answers

Which of the following lasers is specifically indicated for the management of vitiligo?

He-Ne laser Signup and view all the answers

Which laser type is primarily absorbed by melanin and used for hair reduction?

Ruby laser Signup and view all the answers

What is the primary application of the Nd:YAG laser?

Photocoagulation treatments Signup and view all the answers

Which wavelength range corresponds to the Ruby laser?

694 nm Signup and view all the answers

Which laser has the highest wavelength mentioned in the provided content?

Nd:YAG laser Signup and view all the answers

What primarily enables optical fibres to transmit light effectively over long distances?

Total internal reflection within the core Signup and view all the answers

What is the significance of the numerical aperture in optical fibres?

It governs the maximum acceptance angle and controls light divergence. Signup and view all the answers

Which of the following types of fibres typically has a core diameter ranging from 8-10 µm?

Single-mode fibre Signup and view all the answers

In clinical applications involving light for therapeutic purposes, what is typically unnecessary beyond dosimetry or calibration?

Detection of the light itself Signup and view all the answers

What characteristic of the core medium is crucial for maintaining total internal reflection?

Its refractive index must be slightly higher than that of the cladding. Signup and view all the answers

What is a potential application for light in medical settings?

To destroy tumours or reshape the cornea Signup and view all the answers

What is the primary application of the CO₂ laser with a wavelength of 10,600 nm?

Deep laser resurfacing Signup and view all the answers

Which wavelength range of red to near infrared light is most effective for treating aging skin?

650-1000 nm Signup and view all the answers

What is a significant advantage of using optical fibers in light therapy?

Allows for precise delivery of light Signup and view all the answers

Which application is associated with blue to green light in the range of 495-570 nm?

Kill bacteria and control acne Signup and view all the answers

What therapeutic effect is achieved through light in the 570-600 nm range?

Detoxification and sensory nervous system stimulation Signup and view all the answers

Which of the following wavelengths is associated with the treatment of psoriasis, dermatitis, and vitiligo?

380-495 nm Signup and view all the answers

Which of the following wavelengths has low penetration into tissue?

495-570 nm Signup and view all the answers

What is the main effect of using light in the range of 600-650 nm?

Stimulates collagen production Signup and view all the answers

What characteristic of light allows it to be effectively used in photobiomodulation therapy?

Its coupling into optical fibers Signup and view all the answers

Which property is NOT associated with the LED light in the 650-1000 nm range?

Killing bacteria Signup and view all the answers

What primarily causes the intensity of a light beam to decay exponentially when traveling through a scattering medium?

Elastic scattering of photons Signup and view all the answers

Which characteristic distinguishes lasers from light-emitting diodes (LEDs)?

Lasers provide a narrowband output much more than LEDs. Signup and view all the answers

What role does nitrogen (N₂) play in the carbon dioxide laser?

It enhances laser efficiency. Signup and view all the answers

What is the primary mechanism through which superluminescent diodes (SLDs) generate light?

Stimulated emission during electron-hole recombination. Signup and view all the answers

What is a common application of carbon dioxide lasers due to their strong absorption by water?

Laser scalpels and skin resurfacing Signup and view all the answers

What is the main difference between LEDs and superluminescent diodes in terms of light emission?

SLDs generate light with amplified stimulated emission, unlike LEDs. Signup and view all the answers

In terms of light wave behavior, what does transport theory primarily describe?

Statistical mechanics of particle passage through scattering media. Signup and view all the answers

Why are carbon dioxide lasers often utilized for medical procedures involving tissue?

They efficiently vaporize tissue constituents with high water content. Signup and view all the answers

Which feature differentiates incoherent light sources from coherent light sources?

Coherent sources have predictable phase relations between light waves. Signup and view all the answers

Study Notes

Coefficient Scattering

Consider a collimated light beam traveling in the z-direction through a thin, non-absorbing medium that scatters light elastically.
As the beam passes through the medium, some light scatters out of the beam in different directions.
The intensity of the beam decreases exponentially; exp(-μsz).
The probability that a photon is scattered while traveling a short distance between z and z + dz is μsz.

Tissue Propagation Light

Transport theory is the statistical mechanics area that describes the passage of particles (neutrons, photons, molecules) through a scattering medium.
It is only possible to give some statistics about a large population of particles.

Light Detectors and Sources

Incoherent Light Sources: Light Emitting Diodes (LEDs) and Superluminescent Diodes (SLDs).
Lasers (coherent light sources).

Light Emitting Diodes: Superluminescent & Emitting Light

LEDs are semiconductors (p-n junctions) that emit light when electrons and holes recombine at the junction.
LEDs are not narrowband sources like lasers but have a peak wavelength (wide bandwidth).
LEDs are cheap, very reliable and can be modulated at high frequencies.

SLED (or Diode SLED)

These are high power sources of broadband light.
They generate light at p-n junctions, as LEDs do, though with additional amplification due to stimulated emission.

Lasers: Medical Laser CO2

Carbon dioxide laser (λ = 10.6 µm).
Laser levels are vibrational levels of the CO2 molecule, although the active medium also contains He and N2 to improve efficiency.
IR light is strongly absorbed by water, useful for vaporizing tissue (e.g., laser scalpels and resurfacing).
Power of clinical systems typically range from 10-50W.

Lasers: Medical Laser Nd:YAG

Nd:YAG laser (λ = 1064 nm).
A four-level solid-state laser using an yttrium-aluminum-garnet (YAG) crystal doped with neodymium Nd3+ ions.
Pulsed Nd:YAG lasers generate pulses of tens to hundreds of millijoules (mJ).
Clinically used for photodisruption in posterior capsulotomy, photoacoustic imaging, and coagulation.

Lasers: Medical Laser ArF excimer

ArF excimer laser (λ = 193 nm).
Excimer lasers are gas lasers that emit UV wavelengths. 'Excimer' is a contraction of excited-dimer.
The active medium is a gas of diatomic molecules that are bound only in an excited state; returning to the ground state causes atoms to separate.
Molecule in ground state is empty.
Pulsed excimer lasers typically produce ~10ns pulses with 0.2-1 J energy.
Clinically used in corrective laser eye surgery (LASIK).

Lasers: Medical Diode Laser

Laser diodes (λ = 650-2000 nm) are semiconductor lasers with operation similar to superluminescent diodes but use a resonant cavity to form the laser.
Feature advantages include compactness, low cost, and long lifespan.
Available in a wide range of red-NIR wavelengths with output power as high as 50 W for NIR diode arrays.
Clinical applications include NIR spectroscopy, optical imaging, photodynamic therapy, and photocoagulation.

Optics Fibre

Light, particularly laser light, has a significant advantage in its use with optical fibers.
Laser light can easily be coupled into optical fibers allowing precise delivery to the desired location.

Photodiodes

Photodiodes are particularly convenient in endoscopy and minimally invasive surgery where surgical tools need to fit into small holes.
Optical fibers utilize total internal reflection to trap light beams; allowing for transmission over long distances, even into hard-to-reach areas.
Step-index fibers have a core medium where light travels, and a cladding medium surrounding the core. The core's refractive index is slightly higher than the cladding's.
Numerical aperture (NA) governs the maximum acceptance angle and the divergence angle of the light beam as it leaves the fiber.

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Description

Explore the principles of transport theory as it pertains to light scattering in various mediums. This quiz will cover concepts such as coefficient scattering and light sources, including LEDs and lasers. Test your understanding of how light interacts with scattering materials and the detectors involved.