NIGA Flashcards

Question

What are the main requirements for an ideal optical detector

Answer 1

High sensitivity, low noise(high signal to noise ratio), wide spectral range, fast response time, rugged and cost-effective.

Answer 2

Photon detectors: phototubes, photodiodes, photomultipliers and charge-coupled devices (CCDs) Thermal detectors: bolometers, thermocouples and pyroelectric detectors

Answer 3

D* represents the signal to noise ratio for a certain electrical frequency and bandwidth if 1 watt of radiation power reaches a detector surface of 1cm2. The higher D* value is, the better the detector is D*=sqrt(active detector area)/NEP NEP (noise equivalent power) is defined as the signal power that gives a signal to noise ratio of one in a one hertz output bandwidth

Answer 4

-Convert photon energy into electrical signals -Exhibit high sensitivity and fast response times -Operate in the UV-VIS range and are unsuitable for far-IR detection -single or multi channel (1-D or 2-D) - Highly variable spectral response

Answer 5

A phototube comprises a cathode and anode in a vacuum. Incident photons eject electrons from the cathode, creating a photocurrent proportional to the light intensity. The wavelength range depends on the cathode material.

Answer 6

Silicon photodiodes are reverse-biased pn junctions. Incident light creates electron-hole pairs in the depletion region, producing a photocurrent proportional to the light intensity

Answer 7

Photodiode arrays (PDAs) - linear arrays of diodes for simultaneous detection across a spectrum. Charge-coupled devices (CCDs) - high sensitivity and resolution for capturing entire spectra

Answer 8

PDAs are linear arrays of reverse-biased silicon diodes. Each diode measures incident light at specific wavelengths. They are commonly used in spectroscopy.

Answer 9

CTDs, such as CCDs and CIDs, store photon-induced charges in silicon elements. These charges are transferred sequentially to amplifiers for measurement. They offer high sensitivity and spatial resolution.

Answer 10

Thermal transducers absorb radiant energy, causing temperature changes that are measured. They have a flat spectral response, operate in the IR range, and are slower than photon detectors.

Answer 11

A thermocouple uses 2 dissimilar metals joined at a junction. Radiation absorption causes a temperature difference, generating a voltage proportional to the radiant energy.

Answer 12

Bolometers measure changes in resistance caused by absorbed radiation. They are highly sensitive and operate by detecting temperature in blackened materials.

Answer 13

Semiconductor bolometers have higher thermal coefficients of resistance, making them more sensitive to temperature changes compared to metals.

Answer 14

Cooling reduces thermal noise enhancing sensitivity and allowing the detection of weak signals

Answer 15

Pyroelectric transducers use temperature-dependent polarization in crystals. Radiation absorption alters the polarization, generating a measurable current. Materials like LiTaO₃ and TGS are common.

Answer 16

The interference method uses coherent laser light. As a mirror moves, interference fringes form, allowing precise measurements of displacement by counting fringe shifts. Michelson interferometers are common for this application.

Answer 17

Distances up to the laser's coherence length (often 100m or more) can be measured with micrometer accuracy using stabilized lasers.

Answer 18

The michelson interferometer splits laser beam into 2 paths. Reflected beams recombine to form interference fringes, with fringe shifts indicating distance changes.

Answer 19

The polarization interferometer uses polarized beams and measures phase shifts due to displacement

Answer 20

Dual-frequency interferometer uses 2 laser frequencies. Doppler shifts caused by motion are measured to determine displacement.

Answer 21

This interferometer, a modified Michelson, assesses optical surface quality by observing interference fringes caused by slight mirror tilts.

Answer 22

This method measures the time taken for a laser pulse to travel to a target and back. Accuracy depends on pulse duration and timing resolution.

Answer 23

Triangulation uses a laser beam to create a spot on the target. A camera captures the spot's position, and geometric calculations determine the distance. 300nm to 10m range. 0.05% accuracy.

Answer 24

Continuous-wave lasers modulated with sine waves are used. The phase delay between transmitted and received signals determines the range.

Answer 25

Measures velocity using Doppler shifts in reflected light. The frequency change corresponds to the object's speed.

Answer 26

A dual-frequency interferometer measures angular rotation by detecting differences in Doppler shifts between beams reflected from 2 retroreflectors

Answer 27

A modified dual-frequency interferometer splits the laser beam using a Wollaston prism. Deviations in reflected beams measure the straightness of a surface.

Answer 28

Laser beam comes at the surface at an angle, only scattered light reaches diode (Caused by surface irregularities). By analyzing intensity and distribution of scattered light, surface texture and roughness can be assessed

Answer 29

For poultry farming - to prevent male chicken killing (after 9 days of incubation laser burns a tiny hole in the eggs shell, from it drop of allantois fluid is taken) this allows detection of chicken gender. Using NIR-Raman spectroscopy after 3 days of incubation the formed blood vessel systems reflects light and gender is determined from its hemoglobin spectrum. Weed control - lasers are being developed to distinguish weeds from crops using imaging techniques and to weaken weed's growth centers with precise, high-energy pulses, reducing the need for chemical herbicides( could be used in high-quality vegetable growth) Laser leveling - for even soil surface (less water needed, improves crop establishment, faster work, reduced weed problem, uniformity of crop maturity)

Answer 30

Drag scrapper/bucket - mounted or pulled by a tractor. Laser transmitter - mounted on tripod, emits infrared beam that travels up to 500m in a straight line. Laser receiver - senses infrared beam and converts it to electrical signal, multi-directional receiver directs the position of the laser reference plane, transmits signal to the control box. Control box - accepts, processes signals from the receiver, indicates drag buckets position relative to the finished grade. Hydraulic system - supplies oil to raise and lower leveling bucket, several times a second it raises and lowers blades of a grader to follow the infrared beam.

Answer 31

Reduction of time and water for irrigation, uniform water distribution, smoother soil surface, uniform moisture environment for crops, less weeds in the fields, uniformity in crop maturity, reduced seed rate, fertilizers, chemicals and fuel requirements, better germination and growth of a crop

Answer 32

Laser surveying helps avoid assumptions, generalizations, errors in interpretation, problems by having the original data set to refer back to

Answer 33

Scanner emits a laser beam that is reflected from the object. To measure a point's position, the scanner records inclined distance and 2 angles: horizontal (a) and vertical (b). Measurements are converted from polar coordinates to a cartesian coordinate system to determine the point's precise location. The collected data forms a "point cloud" representing the object's surface. Accuracy depends on distance to the object, the angle of incidence, reflective properties of the surface.

Answer 34

Highest absorption of chromophores occurs in the UV and VIS spectral regions, particularly below 1000nm. This is where key chromophores such as hemoglobin, melanin, and other biomolecules exhibit strong absorption. Water strongly absorbs light in the IR spectral regions, particularly beyond 1000nm.

Answer 35

Rayleigh scattering, d << lambda (mitochondria), and Mie scattering, d >= lambda (macromolecules, membrane structures). Scattering of tissue is always a combination of Rayleigh and Mie scattering, depending on what structures are dominant.

Answer 36

Relies on extremely short laser pulses(ns or shorter), high photon spatial density and coherent light. It generates micro-plasma through optical breakdown (intense electric fields tear molecules apart). Micro-plasma expansion creates supersonic shockwaves, leading to mechanical rupture of the tissue

Answer 37

It's evaporation followed by expulsion of evaporated material. Depending on the laser type (e.g. UV lasers), the process can be clean and localized, with minimal heat diffusion, while the interaction volume is determined by the spot size and optical penetration depth. If energy is smaller than needed for evaporation it results in thermal effects.

Answer 38

Rely on selective heating of highly absorbing regions, such as microvessels. Achieved when laser pulse duration is shorter than the thermal diffusion time accross the region ((τ < L²/4D), ensuring thermal energy is confined before diffusing, leading to coagulative or vaporizing effects. L-diffusion length, D-diffusion constant.

Answer 39

Selective cancer-cell targeting by conjugation of absorbing particles; localized tumor destruction; absorption of radiation at longer wavelengths.

Answer 40

Activates photosensitizer by light to produce reactive oxygen species (ROS), primarily singlet oxygen (1O₂) it induces cytotoxic effects in tissues with high photosensitizer concentrations, makes it effective for tumor-targeted therapies.

Answer 41

Uses photodynamic reaction, steps: photosensitizer administration, photosensitizer distribution in body, tumor irradiation, tumor ablation & cure.

Answer 42

Involves low-fluence light, also called low-level laser therapy (LLLT), aimed at promoting cellular repair and recovery, though its efficacy is unclear and not scientifically proven

Answer 43

42-45C start of hyperthermia, collagen shrinkage. 50C Enzyme activity decreases 60C Protein denaturation, collagen coagulation, membrane permeabilization. 100C Tissue drying, vacuole formation. >100C Vaporization, tissue carbonization 300-1000C thermoablation, photoablation, tissue disruption.

Answer 44

delta T - temperature increase Q(J/cm^3) - absorbed thermal energy per unit volume ro (g/cm^3) - density c [J/g*K] - specific heat delta T = Q/(ro*c)[K]

Answer 45

Hair removal, vascular and pigmented lesion treatment (various skin diseases and abnormalities), tatoo removal, skin resurfacing, acne treatment, and scar revision.

Answer 46

Pigment is broken down by shock waves generated in the tissue by very short light pulses from Q switched lasers operating with pulse durations of 2-50ns. Longer pulse duration can be used by targeting entire pigmented lesions.

Answer 47

Uses excimer laser to decrease nearsightness, removes precise amount of tissue from cornea to reduce its curvature using "cold" UV laser. It brings the focal point closer to retina.

Answer 48

Procedure utilizes excimer laser and the microkeratome to alter the degree of near-sightedness in an eye. Creates a flap from cornea, folds it back, then laser removes precise amount of tissue from cornea, folds the flap back.

Answer 49

Reduces nearsightness, radial incisions are made in cornea, with a diamond blade. Incisions flatten the central portion of cornea, brings the focal point closer to the retina, improves distance vision.

Answer 50

Excimer laser is used to reshape cornea to correct farsightedness. Farsighted (hyperopic) cornea is flatter than is required given the length of your eye. Surgery improves vision by reshaping the front surface of the eye and making it more curved.

Answer 51

Uses a laser to make very precise cuts in the eye: creating an opening in the lens capsule and breaking up the cataract. The laser is guided by detailed images of the eye, improving the safety and accuracy of the procedure.

Answer 52

Treatment of neovascular (wet) age-related macular degeneration, choroidal neovascularization. IT targets abnormal blood vessels or tumors with light-activated drugs, reducing fluid and improving retinal health.

Answer 53

Surgical management of oral hard/soft tissue, non-surgical application, antibacterial applications. Restorative dentistry, laser assisted diagnosis, surgical applications, oral diagnosis/oral medicine, oral surgery, periodontics, pediatric, endodontics, biostimulation.

Answer 54

Neodymium YAG; Erbium (Er:YAG and Er,Cr:YSGG) and diode group of semiconductor based technology.

Answer 55

Photo-biomodulation, diagnostics, photo-activated anti-bacterial processes, laser tooth whitening and laser scanning of tooth cavity preparations.

Answer 56

Precise ablation of hard tissue, selective ablation of diseased tissue, less risk of injury, less risk of thermal and mechanical cracking of tooth structure, reduction in bacterial contamination of tooth cavity, less discomfort for patient.

Answer 57

Removal of diseased pocket lining epithelium, bactericidal effect of lasers on pocket organisms, removal of calculus deposits and root surface detoxification.

Answer 58

Treatments for nasal polyps, sinus surgery and turbinate hypertrophy. Also used for vascular malformations, tumor removal, glottis/subglottis procedures, and cosmetic treatments such as rhinophyma correction. Used lasers vary in wavelength and penetration depth to target specific tissues effectively (CO2 and Erbium:YAG)

Answer 59

Used for hemostasis, tumor debulking, palliation of inoperable cancers, treatments of dysphagia, interstitial photocoagulation of liver metastases, treatment of small gastrointestinal tumors.

Answer 60

Lasers in the cardiovascular system are used to treat blocked arteries, remove blood clots, improve blood flow in heart muscle, and treat irregular heartbeats by precisely targeting and removing or reshaping tissue, though further research is needed to address some challenges.

Answer 61

Used to treat brain and spinal tumors, vascular issues, and deep-seated lesion with precision and minimal damage, often through techniques like stereotactic surgery and minimally invasive laser therapies

Answer 62

Using low-coherence light to capture high resolution cross-sectional images of tissues. Light is split into 2 beams: one reflects from the sample and the other from a reference mirror. By analyzing the interference of the reflected beams, detailed depth-resolved images of the sample are generated.

Answer 63

Using near-infrared light to measure the scattering and absorption properties of tissues. By analyzing how light propagates through the tissue, DOT reconstructs 3D images of internal structures, used for examination of biological tissues at a macroscopic scale.

Answer 64

Ability to achieve high spectral resolution and detection sensitivity by providing strong, stable radiation sources, enabling the detection of very small absorption levels and low concentrations of molecules.

Answer 65

It is based on measuring the amount of light absorbed by a sample at specific wavelengths, which provides information about the sample's composition and concentration of molecules. Advantages: Extremely high spectral resolution, enhanced detection sensitivity, the ability to use long absorption paths for detecting weak absorptions, precise calibration of absorption lines and rapid wavelength tuning for studying short-lived molecular species.

Answer 66

Laser excites molecules to a higher energy state, undergoes possible collisional change, and after some delay, they emit fluorescence as they return to a lower energy state. The emitted light is typically observed at a 90deg. angle to the excitation beam, it provides high sensitivity for detecting specific molecules on a dark background.

Answer 67

Sample is excited using external energy source (plasma), it causes them to emit light at characteristic wavelengths. By analyzing this emitted light, the elemental composition of the sample can be determined.

Answer 68

Laser pulses vaporize solid sample, causes breakdown in gas and create a plasma, plasma emits light at characteristic wavelengths, and can be used for elemental analysis.

Answer 69

Early delays dominated by intense continuum emission, intermediate delays show atomic emissions and long delays showing reduced intensity due to plasma cooling. Optimal timing is crucial for capturing desired spectral features.

Answer 70

Laser beam --> focussing objective --> collection lens --> entrance slit of the spectrometer Laser beam --> focusing objective --> collection lenses --> optical fiber to the spectrometer Laser beam --> focussing objective <-- Schwarzschild objective or Cassegrain telescope <-- Optical fiber to the spectrometer Laser beam --> Dichroic mirror -->/--> Focussing and collection objective -->/--> Collection lens --> optical fiber to the spectrometer

Answer 71

It uses light scattering to study gases: Rayleigh scattering helps measure density and temperature, while Raman scattering identifies molecules and their energy levels. Rayleigh is stronger and cleaner, but Raman gives more detailed chemical information

Answer 72

Rayleigh scattering is elastic, strong, and ideal for imaging density and temperature with minimal background, while Raman scattering is inelastic, weaker, and used for identifying multiple molecular species and temperature but often suffers from background interference.

Answer 73

It amplifies Raman signals by placing analyte molecules near metal nanoparticles, where localized surface plasmons create "hot spots" that enhance the electromagnetic field, significantly increasing sensitivity for molecular detection.

Answer 74

Laser > photodiode > discriminator > time-to-voltage converter /> multichannel analyzer /> discriminator > photomultiplier > sample It splits laser pulse, one part starting a timer and the other exciting the sample. The timer runs until it is stopped by a fluorescence photon emitted from the sample, detected by a photon counting device. Repeating this process many times creates a histogram of fluorescence decay, provides sample's fluorescence lifetime.

Answer 75

Light --- Electrions --- light Entrance slit > Entrance optics > photocathode > acceleration grid > deflection electrodes > microchannel plate > phosphor screen > Exit optics > CCD camera Fluorescence photons are converted into electrons at a photocathode. Electrons are accelerated and deflected by a sweeping voltage, it converts their arrival time into position in space. Process is synchronized with the laser pulse, and the deflected electrons create an image on a phosphor screen, which is then captured by a CCD camera.

Answer 76

BS /> RR > BBO2 > CCD BS /> BBO1 > BPF > 400nm > sample > LPF > BBO2 > CCD Pulse is split into 2, gate is delayed by the optical delay line, other is used to excite sample. Emitted fluorescence is collected using parabolic reflectors and focused into BBO2 crystal together with delayed gate pulse. BBO2 generates sum frequency between gate and fluorescence, its spectrum is spread by monochromator and recorded by CCD detector

Answer 77

Gate pulse + fluorescence > polarizer > nonlinear medium > polarizer > spectrograph > CCD Fluorescence passes 2 crossed polarizers and nonlinear medium, the gate pulse hits medium, polarization of fluorescence light is rotated and the light overlapping with gate pulse is transmitted through second polarizer.

Answer 78

Pump pulse excites the sample, while a probe pulse measures how the sample's transmittance changes over time. By varying the delay between the pump and probe pulses, the time-dependent absorption signal is recorded.