Infrared, Lasers & Fiber Optics (2018)

Question 1

List some of the advantages of IR over radar.

Answer 1

Less susceptible to detection and interference. IR equipment is usually less complex

Question 2

Define remote sensing.

Answer 2

Remote sensing is the process of detecting or sensing infrared radiation from a target without being in physical contact with that target.

Question 3

List the similar characteristics of infrared and light.

Answer 3

reflection, refraction, absorption and speed of transmission

Question 4

What frequencies of the electromagnetic spectrum are considered to be in the IR
frequency range?

Answer 4

About 300 gigahertz to about 400 tetrahertz

Question 5

Name the three IR bands of the electro- magnetic spectrum.

Answer 5

1. near infrared (NIR)
2. intermediate infrared (IIR)
3. far infrared (FIR)

Question 6

List the advantages in using IR for target detection.

Answer 6

1. IR systems are passive
2. complete jamming is difficult
3. military targets are good sources.
4. IR systems are smaller, lighter, less complex, and less expensive.
5. IR systems have a high target resolution

Question 7

What is the blackbody concept?

Answer 7

an object that absorbs all radiation incident on it and emits the maximum radiation for any given temperature.

Question 8

Of all the parameters in determining IR characteristics, which one is the most important, and why?

Answer 8

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.

Question 9

What is the primary factor that affects the IR transmitting medium and its primary cause?

Answer 9

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.

Question 10

Absorption is the major cause of attenuation in IR system design. What happens at higher altitudes?

Answer 10

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.

Question 11

List the problems involved when designing IR optical systems.

Answer 11

1. the material used must match the wavelength the detector responds to.
2. optical materials are physically weak and damage easily by high temperature and thermal shock.
3. pressure and chemical reactions can change the properties of some optical materials.

Question 12

Optical filters isolate certain wavelengths and screen out undesired wavelengths. What are the three general types of filters?

Answer 12

1. Those that pass short waves
2. Those that pass a particular band of waves.
3. Those that pass long waves.

Question 13

What is the most critical component of any IR system?

Answer 13

detector

Question 14

List the most common types of detectors.

Answer 14

Bolometers
Golay cells
mercury-doped germanium
lead sulfate
phototubes

Question 15

Define responsivity as it relates to the detector.

Answer 15

The amount of output signal that each unit of input radiation intensity produces.

Question 16

What are two of the most important types of noise generated by an IR system?

Answer 16

1. Current noise caused by bias currents within the detector.
2. Johnson noise caused by thermal fluctuations in the detector material.

Question 17

Name the two basic types of energy-matter interaction.

Answer 17

Photon and thermal effect

Question 18

What are the three major types of photo- detectors?

Answer 18

Photoconductive
photovoltaic
photoemissive

Question 19

Three different types of sensing elements are used in modern thermal detectors. What are they?

Answer 19

1. Thermophile-series combination of several thermocouples.
2. Bolometer- senses changes in resistances of the detector material.
3. Pneumatic cell-uses the expansion of a gas as an indicator

Question 20

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?

Answer 20

it can operate only when intermittently receiving radiant heat.

Question 21

There are many uses for infrared, including short-range communication, navigation, and anticollision circuit experimentation. Why is infrared used in photography?

Answer 21

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.

Question 22

Name the three types of homing systems classified by their source of radiation.

Answer 22

Active
semi active
passive

Question 23

List some of the components of a typical infrared imaging system.

Answer 23

detectors 
a scene disection system
front end optics
refrigeration system
image processing system

Question 24

What is the purpose of front end optics?

Answer 24

collect the incoming radiant energy and focuses the image at the detectors

Question 25

Why do some infrared imaging systems need refrigeration systems?

Answer 25

it provides the necessary operating temperatures for imaging systems.

Question 26

Name some of the elements and components of a scanning infrared imaging system.

Answer 26

``` stabilization and pointing gimbals collecting optics and filters optpmechanical scanner scan encoders scan synchronizer detector assembly video processor ```

Question 27

Define cyrogenics and identify its temperature range.

Answer 27

its the science that involves the study of very low temperatures. -150 C downward to -273 C

Question 28

What happens when bodies of different temperatures meet in thermal contact?

Answer 28

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.

Question 29

Energy is the driving force of the universe. What assumptions can you make about energy?

Answer 29

1. Energy is the fuel required to make things happen 2. no system can operate without a transfer or energy 3. heat is a form of energy

Question 30

How does heat flow through radiation?

Answer 30

electromagnetic radiation.

Question 31

Describe the basic principle of a laser

Answer 31

a device that produces or amplifies ultraviolet, visible, or infrared radiation by controlled stimulated emission.

Question 32

What determines the wavelength (or color) of light emitted by a laser?

Answer 32

type of material used in the laser

Question 33

Some terms are useful in dealing with lasers. These include watts, joules, and irradiance. What is meant by irradiance?

Answer 33

the amount of power per unit area.

Question 34

What is meant by a diffuse surface?

Answer 34

a surface that reflects the incident laser beam in all directions.

Question 35

Explain wave optics.

Answer 35

Wave optics involve the reflection or absorption of waves. Light strikes an object or medium and is either reflected or absorbed.

Question 36

Name two categories of lenses.

Answer 36

Converging and diverging.

Question 37

What is the particle theory of light?

Answer 37

The particle theory of light states that “light is composed of particles called photons, which are bundles of massless energy.”

Question 38

What is meant by stimulated emission

Answer 38

equal to the transition energy of the excited atom; the excited atom triggers or stimulates an emission from atom two.

Question 39

List the five categories in which most lasers are grouped.

Answer 39

1. Solid state 2. gas 3. ion 4. chemical 5. dye.

Question 40

A basic fiber optic system consists of a transmitter, a fiber medium, and a receiver. Describe the basic technique of fiber optics.

Answer 40

the technique of sending data, in the form of light, through long, thin, flexible fibers of glass, plastic, or other transparent materials.

Question 41

List the advantages of fiber optic systems.

Answer 41

1. Usable in flammable areas 2. Immune to noises generated by RFI, EMI, lightning, and cross talk 3. Immune to electromagnetic pulse effects 4. Not affected by moisture or temperature changes (e) Easy to repair 5. Very high transmission rates 6. Small size and lightweight

Question 42

By what means does light travel through a fiber optic?

Answer 42

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.

Question 43

What is the difference between single-mode and multi-mode operation?

Answer 43

Single-mode types accept a specific wavelength, otherwise, large attenuation results. Multi-mode types operate over a range of wavelengths, with minimum signal loss.

Question 44

Attenuation is the loss or reduction of energy transmitted. Efforts to reduce these losses include the forming of standard parameters. What are these parameters?

Answer 44

1. Bandwidth parameters provide designers the ability to choose the best fiber. 2. Rise time parameters set the speed requirements for fiber operation. 3. Fiber strength parameters set tensile strength requirements to help reduce flaws and microcracks in the fiber.