Podcast
Questions and Answers
What is the typical duration for measurements when using an integrating sphere?
What is the typical duration for measurements when using an integrating sphere?
Lasers and novel broadband sources give consistent and satisfactory results in all cases.
Lasers and novel broadband sources give consistent and satisfactory results in all cases.
False
What is the purpose of a spectro-radiometer in precise work?
What is the purpose of a spectro-radiometer in precise work?
To investigate the spectra of light sources.
The __________ is the ratio of velocity in a vacuum to that of the medium.
The __________ is the ratio of velocity in a vacuum to that of the medium.
Signup and view all the answers
Match the optical concepts with their definitions:
Match the optical concepts with their definitions:
Signup and view all the answers
What is a common type of measurement device for laser power?
What is a common type of measurement device for laser power?
Signup and view all the answers
The maximum power density for thermopiles is typically 10 GWcm-2.
The maximum power density for thermopiles is typically 10 GWcm-2.
Signup and view all the answers
What principle do thermocouples operate on to measure temperature?
What principle do thermocouples operate on to measure temperature?
Signup and view all the answers
A Si photo diode uses ___________ to indicate power.
A Si photo diode uses ___________ to indicate power.
Signup and view all the answers
Match the following delivery methods with their descriptions:
Match the following delivery methods with their descriptions:
Signup and view all the answers
What is a typical maximum power handling capability for thermopiles?
What is a typical maximum power handling capability for thermopiles?
Signup and view all the answers
Photodiodes have a longer response time compared to thermopiles.
Photodiodes have a longer response time compared to thermopiles.
Signup and view all the answers
What is the typical diameter of the sensor used for laser beam measurement?
What is the typical diameter of the sensor used for laser beam measurement?
Signup and view all the answers
What happens to the reflection at a smooth air-glass interface as the angle of incidence increases?
What happens to the reflection at a smooth air-glass interface as the angle of incidence increases?
Signup and view all the answers
Total internal reflection occurs at Brewster’s Angle when the reflected intensity is equal to the incident intensity.
Total internal reflection occurs at Brewster’s Angle when the reflected intensity is equal to the incident intensity.
Signup and view all the answers
What is the primary purpose of an optical fibre?
What is the primary purpose of an optical fibre?
Signup and view all the answers
The refractive index of air is _____
The refractive index of air is _____
Signup and view all the answers
Match the property with its corresponding description:
Match the property with its corresponding description:
Signup and view all the answers
What does the numerical aperture (NA) refer to?
What does the numerical aperture (NA) refer to?
Signup and view all the answers
Snell's Law describes the relationship between the angles of incidence and refraction at an interface.
Snell's Law describes the relationship between the angles of incidence and refraction at an interface.
Signup and view all the answers
Identify the angle of incidence at which total internal reflection occurs in glass.
Identify the angle of incidence at which total internal reflection occurs in glass.
Signup and view all the answers
Which type of fibre is typically used for communication due to its low signal noise?
Which type of fibre is typically used for communication due to its low signal noise?
Signup and view all the answers
The numerical aperture (NA) determines the cone of acceptance in fibre optics.
The numerical aperture (NA) determines the cone of acceptance in fibre optics.
Signup and view all the answers
What is the numerical aperture (NA) value for the fibre described in the content?
What is the numerical aperture (NA) value for the fibre described in the content?
Signup and view all the answers
The apex angle of the cone of acceptance is defined by the numerical ______.
The apex angle of the cone of acceptance is defined by the numerical ______.
Signup and view all the answers
Match the types of fibres with their characteristics:
Match the types of fibres with their characteristics:
Signup and view all the answers
For a plane fibre delivering into air, what happens to the output cone?
For a plane fibre delivering into air, what happens to the output cone?
Signup and view all the answers
Silica glass is known for having high loss and is commonly used for optical fibres.
Silica glass is known for having high loss and is commonly used for optical fibres.
Signup and view all the answers
Name a type of glass mentioned in the content that includes Zirconium, Barium, Lanthanum, and Aluminium.
Name a type of glass mentioned in the content that includes Zirconium, Barium, Lanthanum, and Aluminium.
Signup and view all the answers
Study Notes
Power Measurement and Laser Delivery Systems
- Medical physics and INIR specifications are covered.
- Measurement tools, fiber optic delivery, articulated arm delivery, hollow wave-guide delivery, and hand-pieces are included in the lecture outline.
- Safety signs and signals, guidance on health and safety regulations, are referenced.
Laser Power Meter
- All medical lasers feature integrated displays estimating power based on selected factors.
- Engineers need to measure power when servicing or employing new techniques, and more regularly for specialist procedures like PDT.
- Thermopiles or photodiodes are common power measurement devices.
Thermopile
- Consists of a bank of thermocouples.
- Measures temperature using the Seebeck Effect.
- Indicates laser power.
- Two dissimilar metals, joined together, form junctions heated or cooled.
- Voltage change indicates temperature.
- The cold end is maintained at ambient temperature.
Photodiode Detectors
- Utilizes a silicon photodiode.
- Measures current to indicate power.
- Voltage relates to temperature.
- Highly specialized and wavelength-specific.
- Quick response time.
- Limited to a few mW continuous power.
Questions Relating to Thermopiles
- Sensor size is typically around 10mm diameter.
- Matte black surfaces absorb approximately 98% of incident light.
- Good wavelength response, typically a few percent from 200–20,000nm.
- Maximum power handling is usually 10W.
- Maximum average power density is ~10kW/cm².
- Damage threshold is ~ 10 GW/cm².
- Typically, response time is 1–2 seconds.
Integrating Sphere
- Diffuse reflections from the inner surface of a sphere measure laser power from a broad beam source.
- Output is independent of beam shape and geometry.
Spectro-Radiometer
- Simple power outputs can suffice for lasers with well-known properties.
- Unknown or novel broadband sources (LEDs, Xenon lamps) may yield inconsistent or unsatisfactory results.
- Precise data (like for PDT) needs spectro-radiometer investigation.
Fiber Optics: Total Internal Reflection
- Reflection/refraction occur when optical radiation encounters a boundary with differing wave velocities.
- Refractive index (n) is the ratio of velocity in a vacuum to that of the medium (e.g., water = 1.33; glass ≈ 1.5).
- For air to medium with refractive index n : reflected/incident ≈ [(n-1)/(n+1)]².
- Fresnel equations explain wave behavior at interfaces.
- Incident, reflected, and transmitted beams lie in the same plane.
- Reflection/refraction angle obeys Snell's Law.
- Fiber optics are formed by a transparent core surrounded by a cladding with a slightly lower refractive index.
- Maximum acceptance angle, θ, is defined by the numerical aperture (NA) as n₁sinθ = √(n₁² - n₂²), where n₁ is the core refractive index and n₂ is the cladding refractive index.
- Numerical aperture is normally referred to as the NA.
- The output cone for a plane fibre delivering into air equals the input cone's acceptance cone.
- In urological procedures, NA remains constant, but the delivery cone differs.
Modes for Fibres
- Multimode fibres (often used in surgery) allow a range of harmonics, improving illumination.
- Communication fibres are typically graded or single-mode.
- Graded index fibres reduce signal noise and enable longer distances.
Materials for Fibres and Lenses
- Common materials include silica glass (for near-infrared, low loss), and specialized materials (e.g., ZBLAN, for specific lasers).
- Plastic optical fibre (POF) is inexpensive, but has high loss and seldom offers a gradable index.
- Suitability for CO2 and other materials depends on losses, cost, and fabrication difficulties.
Hollow Waveguides
- Far-infrared transmission can be challenging due to high Fresnel loss (over 25%) within the core.
- Hollow waveguides (air cores) are under development, potentially with lower loss.
Coupling into Fibres
- Illuminating beams need to match the fiber's acceptance cone and focus to roughly the same size as the fiber core.
CO₂ Beam Delivery through Articulated Arms
- Hollow tubes with mirrors at each turn deliver the CO₂ beam.
CO₂ Beam Delivery through Articulated Arm Mirrors
- Copper or gold mirrors are selected for their reflectivity and ability to maintain flat surfaces.
Lenses
- Zinc Selenide lenses are the only material that is transparent to both treatment and aiming CO₂ beams at treatment sites.
CO₂ Handpieces
- Various handpieces cater to different tasks, including positioning spacers to regulate target distance.
Fibres Bundles in Endoscopy
- Endoscopy uses fibre bundles consisting of filaments (3-4 microns) of Ge-doped silica glass for illumination and imaging.
Imaging and Illumination Parameters in Endoscopy
- Crosstalk (light and signal leakage) influences image clarity.
- Illumination level depends on core diameters.
- Image resolution depends inversely on diameter (1/2d).
- Contrast is affected by light intensity.
- Core area ratio to whole bundle is approximately 50%.
- Defects and ordering errors also reduce image quality.
Laser-Induced Fluorescence Imaging
- Topical and in-vivo laser illumination induce wavelength-specific fluorescence from tagged agents.
- These agents are "fluoro-pharmaceuticals," aiding imaging and analysis externally, and also can be used endoscopically.
Laser-Initiated Raman Spectroscopy
- Inelastic Raman scattering identifies spectral patterns of pre-cancerous proteins.
- Special Raman nanoparticles target specific tumour types.
Case Study
- You need to analyze a commercially available novel laser application enabling either diagnosis or therapy.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Explore the intricacies of power measurement and laser delivery systems in medical physics. This quiz covers various measurement tools, delivery methods, and safety guidelines, essential for understanding laser applications in healthcare. Test your knowledge on thermopiles and photodiodes as well.
