Laser Concepts and Physics

Question 1

The Ultra violet range of electromagnetic spectrum is

Answer 1

100-280nm (UBC) , 280-315 nm (UBB), 315- 500nm (UBA)

Question 2

The visible range of electromagnetic spectrum is

Answer 2

400-700nm

Question 3

The Infrared ray range of electromagnetic spectrum is

Answer 3

700-1400nm (IRA), 1400-3000nm (IRB), 3000- 10000

Question 4

Reflection is:

Answer 4

Changing of direction of light as it hits a surface, specular and diffuse

Question 5

Refraction is:

Answer 5

Bending of light as it moves between mediums of differing density

Question 6

Specular reflections occurs:

Answer 6

when lights hits a surface with surface irregularities smaller than the wavelength of incident radiation e.g mirror

Question 7

Diffuse reflections occurs:

Answer 7

when light hits randomly oriented surface with wavelength greater than that of incident radiation e.g wall surface

Question 8

Diffuse reflections are also called

Answer 8

lambertian reflection, visibility of the object is define by it

Question 9

Index of refraction (n) =

Answer 9

speed of light in vacuum (c)/speed of light in medium…depends upon the density of medium

Question 10

Lenses and prisms operate under the principle of

Answer 10

Refraction

Question 11

Snells law

Answer 11

sin Θ incidence/sin Θ refraction= n2/n1

Θ incidence = Θ reflection

Question 12

Diffraction is

Answer 12

bending or spreading of waves after passing an edge or through small opening. This is the results of constructive and destructive interference of near by waves that causes different patterns of light and dark

Question 13

SI system has

Answer 13

Fundamental Units : m, kg , s
Derived units: N, J, W
Units based on biological response: Lumen & Candela
Lumen: amount of light emitted by the source
Candela: measure of power emitted by the source in particular direction

Question 14

Radiometric system is

Answer 14

measure of energy or power

Question 15

Photo-metric system

Answer 15

ability of optical radiation to be sensed by the eye

Question 16

Optical Energy (Q or W)

Answer 16

measured in joules (radiant energy )

Question 17

Optical Power ( or P)

Answer 17

measured in watts ( radiant flux)

Question 18

Irradiance (E)

Answer 18

optical power per unit area ( watt/m2)

Question 19

Radiant Exposure (H)

Answer 19

optical energy per unit area ( joules/m2)

Question 20

Luminance

Answer 20

measurement of light leaving the surface (cd/m2)

Question 21

Illuminance

Answer 21

measurement of the brightness of light hitting a surface ( lux(lx) or lumens/m2)

Question 22

Laser is

Answer 22

Light Amplification by the stimulated emission of radiation.
Monochromatic
Directional
Coherent

Question 23

Divergence (φ)

Answer 23

measure of how quickly a beam spreads.
expressed in miliradians
low divergence means lasers can present a hazard from very far away
φ( radians)= (beam diameter @ distance r)/(r ( distance in meter))

Question 24

Components of Laser

Answer 24

Lasing medium: determines the characteristic of laser ( solid, gas, liquid dye)

Excitation mechanism: External source of energy applied to lasing medium, electrical optical or chemical energy

Optical resonator: totally reflective and partially reflective mirror ( output coupler)

Question 25

Continuous Wave laser

Answer 25

constant output over time ( watts)..

Question 26

Repetitively pulsed laser

Answer 26

laser energy emitted in pulses of a distinct pulse energy

pulse width at the half max energy of each pulse

Question 27

Pulse repetition time

Answer 27

start of one pulse to next pulse ( one peak to next peak)

Question 28

Pulse repetition rate

Answer 28

amount of pulses per second ( Hz) PRT= 1/PRR

Question 29

Q switched Laser

Answer 29

release very high energy released in short period of time

Question 30

Solid State Lasers

Answer 30

Glass or crystalline matrix containing impurity ( dopant). Dopant determines the characteristic of laser
first laser : ruby laser
Nd: YAG : neodymium- doped yttrium aluminum garnet ( can operate in CW or in pulsed modes)
1064 nm….frequency double 532nm

Question 31

Gas Lasers

Answer 31

pure or mix of gas.

excimer laser is combination of a noble gas and a reactive gas ( widely used in eye surgery, lasic eye surgery)

Question 32

Co2 laser wavelength

Answer 32

10,600nm, use for cutting

Question 33

HeNe laser wavelength

Answer 33

633nm

Question 34

Ar laser wavelength

Answer 34

458, 488 and 514.5 nm

Question 35

Semiconductor/Diode Laser

Answer 35

n-type and p-type semiconducting materials…..most commonly used, used in everything from laser pointers to CD?DVD players, laser printing and more

Question 36

Dye Lasers are

Answer 36

Tunable wavelengths, optical energy ( could be flash lamp) used for excitation, organic dyes used as lasing medium.
Rhodamine 6G Chloride- 532 nm…even a laser is used as excitation medium

Question 37

Industrial uses

Answer 37

welding, cutting , etching

Question 38

Research uses

Answer 38

spectroscopy, confocal microscopy, cell marker detection, cell sorting, optics and physics

Question 39

Commercial use

Answer 39

scanners, laser printers, CD/DVD/Blu-ray

Question 40

Military uses

Answer 40

Range finding, weapons targer, directed energy weapons

Question 41

Medical and Dental user+

Answer 41

Surgery: Photocoagulation

Photo ablation- lasic reshape the cornea
Photodisruption- tissue to heatup and destroy ( tumor)
For driling in dental use