Infrared, Lasers & Fiber Optics (2018) Flashcards
List some of the advantages of IR over radar.
Less susceptible to detection and interference. IR equipment is usually less complex
Define remote sensing.
Remote sensing is the process of detecting or sensing infrared radiation from a target without being in physical contact with that target.
List the similar characteristics of infrared and light.
reflection, refraction, absorption and speed of transmission
What frequencies of the electromagnetic spectrum are considered to be in the IR
frequency range?
About 300 gigahertz to about 400 tetrahertz
Name the three IR bands of the electro- magnetic spectrum.
- near infrared (NIR)
- intermediate infrared (IIR)
- far infrared (FIR)
List the advantages in using IR for target detection.
- IR systems are passive
- complete jamming is difficult
- military targets are good sources.
- IR systems are smaller, lighter, less complex, and less expensive.
- IR systems have a high target resolution
What is the blackbody concept?
an object that absorbs all radiation incident on it and emits the maximum radiation for any given temperature.
Of all the parameters in determining IR characteristics, which one is the most important, and why?
temperature is the most important parameter in determining the IR characteristics of any body. as temperature of an object changes, the wavelength where peak radiation occurs shifts, and the total energy radiated varies.
What is the primary factor that affects the IR transmitting medium and its primary cause?
The effect of atmospheric attenuation on transmission is a very important factor in considering the overall effectiveness of the system. The 2 primary causes are scattering by suspended particles and absorption by free molecules in the atmosphere.
Absorption is the major cause of attenuation in IR system design. What happens at higher altitudes?
The absorption bands are much narrower at high altitudes because the atmosphere is thinner; therefore, there are less considerations in designing high altitude IR systems.
List the problems involved when designing IR optical systems.
- the material used must match the wavelength the detector responds to.
- optical materials are physically weak and damage easily by high temperature and thermal shock.
- pressure and chemical reactions can change the properties of some optical materials.
Optical filters isolate certain wavelengths and screen out undesired wavelengths. What are the three general types of filters?
- Those that pass short waves
- Those that pass a particular band of waves.
- Those that pass long waves.
What is the most critical component of any IR system?
detector
List the most common types of detectors.
Bolometers Golay cells mercury-doped germanium lead sulfate phototubes
Define responsivity as it relates to the detector.
The amount of output signal that each unit of input radiation intensity produces.
What are two of the most important types of noise generated by an IR system?
- Current noise caused by bias currents within the detector.
- Johnson noise caused by thermal fluctuations in the detector material.
Name the two basic types of energy-matter interaction.
Photon and thermal effect
What are the three major types of photo- detectors?
Photoconductive
photovoltaic
photoemissive
Three different types of sensing elements are used in modern thermal detectors. What are they?
- Thermophile-series combination of several thermocouples.
- Bolometer- senses changes in resistances of the detector material.
- Pneumatic cell-uses the expansion of a gas as an indicator
The Golay detector has the most rapid response of any infrared detector, but it requires an optical chopper. Why does it need the optical chopper?
it can operate only when intermittently receiving radiant heat.
There are many uses for infrared, including short-range communication, navigation, and anticollision circuit experimentation. Why is infrared used in photography?
photography uses infrared because it is effective against camouflaged targets, and night photography can produce a better visual presentation of terrain than the best mapping radar.
Name the three types of homing systems classified by their source of radiation.
Active
semi active
passive
List some of the components of a typical infrared imaging system.
detectors a scene disection system front end optics refrigeration system image processing system
What is the purpose of front end optics?
collect the incoming radiant energy and focuses the image at the detectors
Why do some infrared imaging systems need refrigeration systems?
it provides the necessary operating temperatures for imaging systems.
Name some of the elements and components of a scanning infrared imaging system.
stabilization and pointing gimbals collecting optics and filters optpmechanical scanner scan encoders scan synchronizer detector assembly video processor
Define cyrogenics and identify its temperature range.
its the science that involves the study of very low temperatures. -150 C downward to -273 C
What happens when bodies of different temperatures meet in thermal contact?
heat flows from the body at the higher temperature to the body at the lower temperature. the flow of heat stops with the two bodies are the same temperature.
Energy is the driving force of the universe. What assumptions can you make about energy?
- Energy is the fuel required to make things happen
- no system can operate without a transfer or energy
- heat is a form of energy
How does heat flow through radiation?
electromagnetic radiation.
Describe the basic principle of a laser
a device that produces or amplifies ultraviolet, visible, or infrared radiation by controlled stimulated emission.
What determines the wavelength (or color) of light emitted by a laser?
type of material used in the laser
Some terms are useful in dealing with lasers. These include watts, joules, and irradiance. What is meant by irradiance?
the amount of power per unit area.
What is meant by a diffuse surface?
a surface that reflects the incident laser beam in all directions.
Explain wave optics.
Wave optics involve the reflection or absorption of waves. Light strikes an object or medium and is either reflected or absorbed.
Name two categories of lenses.
Converging and diverging.
What is the particle theory of light?
The particle theory of light states that “light is composed of particles called photons, which are bundles of massless energy.”
What is meant by stimulated emission
equal to the transition energy of the excited atom; the excited atom triggers or stimulates an emission from atom two.
List the five categories in which most lasers are grouped.
- Solid state
- gas
- ion
- chemical
- dye.
A basic fiber optic system consists of a transmitter, a fiber medium, and a receiver. Describe the basic technique of fiber optics.
the technique of sending data, in the form of light, through long, thin, flexible fibers of glass, plastic, or other transparent materials.
List the advantages of fiber optic systems.
- Usable in flammable areas
- Immune to noises generated by RFI, EMI, lightning, and cross talk
- Immune to electromagnetic pulse effects
- Not affected by moisture or temperature changes (e) Easy to repair
- Very high transmission rates
- Small size and lightweight
By what means does light travel through a fiber optic?
The light injected into a fiber travels in a series of reflections from wall to wall between core and cladding. The reflections depend on the cone of acceptance and resulting angles of refraction and reflection propagation.
What is the difference between single-mode and multi-mode operation?
Single-mode types accept a specific wavelength, otherwise, large attenuation results. Multi-mode types operate over a range of wavelengths, with minimum signal loss.
Attenuation is the loss or reduction of energy transmitted. Efforts to reduce these losses include the forming of standard
parameters. What are these parameters?
- Bandwidth parameters provide designers the ability to choose the best fiber.
- Rise time parameters set the speed requirements for fiber operation.
- Fiber strength parameters set tensile strength requirements to help reduce flaws and microcracks in the fiber.
