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OPTI510R: Photonics

Khanh Kieu College of Optical Sciences, University of Arizona [email protected] Meinel building R.626 Important announcements

 Homework #1 assigned, due Jan 29

 No class Wednesday Jan 24th

 TA office hour: 1-2 PM, Tuesdays (8th floor breakout area) Properties of

of light

 Velocity of light

 Frequency and

 Coherence

 Other light characteristics Nature of light

The nature of light has been a fascinating topic for many generations of researchers. We all see and feel light but what it is exactly is still something that challenges our minds.

17th century known facts about light:

• Light has different colors • Light can travel through • Light can be reflected and refracted

i r

 =  i r (Snell’s law) Nature of light

So what is light?

Corpuscular theory of light: light consists of corpuscles or very small particles flying at a finite velocity (Isaac ).

Can be used to understand , and different colors of light

But fails to explain , interference and polarization of light

Isaac Newton Nature of light

The theory of light: At first, the nature of light is thought of as wave propagating in a medium called . But all attempts to detect the aether have failed so far. So the theory based on the aether was more or less abandoned. The electromagnetic theory of light was then developed, culminating in the Maxwell’s equations. In modern understanding, aether has no role in the theory of light.

(1629-1695) The Michelson–Morley experiment (1887)  In 1845, discovered Faraday rotation

 In 1873, Maxwell published his set of equations

wikipedia.com Nature of light

The wave theory of light: At first, the nature of light is thought of as wave propagating in a medium called luminiferous aether. But all attempts to detect the aether have failed so far. So the theory based on the aether was more or less abandoned. The electromagnetic theory of light was then developed, culminating in the Maxwell’s equations. In modern understanding, aether has no role in the theory of light.

 Christiaan Huygens (1629-1695)

 In 1845, Michael Faraday discovered Reflection, refraction, diffraction, Faraday rotation Interference, and polarization explained

 In 1873, Maxwell published his set of equations Electromagnetic (EM) Infrared-waves

 Wavelength dimensions of sub-mm to micron

 Infrared waves are thermal

Infrared LED in remote control Image of a small dog in mid-infrared light Infrared-waves

 Telecommunication bands

 Thermal imaging, remote sensing

Measuring the temperatures of clouds Visible-waves

 Wavelength dimensions of 0.38 to 0.78 microns

 Human eye is most sensitive at 555mm Ultraviolet-waves

 Wavelength dimensions of 10 to 200 nm

 Sun emits UV radiation. Prolong exposure is bad for skin, eye and immune system. Exposure is needed for generation of Vitamin D. Nature of light

The wave theory of light: At first, the nature of light is thought of as wave propagating in a medium called luminiferous aether. But all attempts to detect the aether have failed so far. So the theory based on the aether was more or less abandoned. The electromagnetic theory of light was then developed, culminating in the Maxwell’s equations. In modern understanding, aether has no role in the theory of light.

 Christiaan Huygens (1629-1695)

 In 1845, Michael Faraday discovered Reflection, refraction, diffraction, Faraday rotation Interference, and polarization explained

 In 1873, Maxwell published his set of equations But… , radiation, Compton effect not explained Nature of light

The classical was completely wrong! (It said that an infinite amount of energy should be radiated by an object at finite temperature)

The quantum theory of light: In an attempt to explain blackbody radiation, Planck postulated that electromagnetic energy could be emitted only in quantized form, in other words, the energy could only be a multiple of an elementary unit, , where h is Planck's constant.

 Different EM waves have diff. E  h  hc / 

 Planck constant: h = 6.626068 x 10-34 m2kg/s

The corpuscular theory of light came back? Nature of light

Wave-particle duality: OK! It must be both wave and particle then! de Broglie formulated the de Broglie hypothesis in 1924- all has a wave- like structure (1929 Nobel prize):

Confirmed by electron Interference (1937 Nobel prize)

wordpress.com

Book by de Broglie Velocity of light

The velocity of light is a fundamental constant in physics. c = 299,792,458m/s

 Maxwell proposed that light travel with the 1865.

 Einstein postulated that the speed of light with respect to any inertial frame is independent of the motion of the light source.

 According to , c is the maximum speed at which all energy, matter, and information in the universe can travel.

 At the moment the meter is defined through the speed of light

How to measure the velocity of light? Measure the velocity of light

Rømer Observation: Delay in the time of eclipses of the moon as observed from earth Measure the velocity of light

Fizeau apparatus Foucault apparatus (c = 315000 km/s) (c = 298000±500 km/s)

Source: wikipedia.com Measure the velocity of light Measure the velocity of light

• In 1983: "The meter is the length of the path travelled by light in vacuum during a time interval of 1/299792458 of a second.“

• As a result of this definition, the value of the speed of light in vacuum is exactly 299 792 458 m/s Measure the velocity of light

1675 Rømer and Huygens, 220000  Astronomical measurements moons of Jupiter 1729 James Bradley, 301000 of light  Time of flight measurement 1849 , 315000 toothed wheel 1862 Léon Foucault, 298000±500  Cavity resonance rotating mirror 1907 Rosa and Dorsey, EM 299710±30 constants  Electromagnetic constants 1926 Albert Michelson, 299796±4 rotating mirror 1950 Essen and Gordon- 299792.5±3.0  Smith, cavity

1958 K.D. Froome, 299792.50±0.10 radio interferometry

1972 Evenson et al., 299792.4562±0.0011 laser interferometry

1983 17th CGPM, 299792.458 (exact) definition of the metre Velocity of light-Practical uses

 LiDAR

 3D imaging

Wikipedia.com  GPS

http://theexceptioncatcher.com/p/GizGPSBth#.Ut8x2vTn-IU osa-opn.org Frequency and wavelength of light Frequency and wavelength of light

The wavelength of light changes in a medium.

How about the frequency?

The wavelength of light defines the smallest spot size that the laser beam can be focused down to.

Diffraction limit How to measure frequency and wavelength of light?

The oscillation frequency of visible light is too fast to be measured with conventional electronics directly.

OSA (Optical analyzer) How to measure frequency and wavelength of light?

Fourier-transform spectrometer

A high-resolution spectrum of CO2 in the near-IR was obtained using a Fourier-transform spectrometer (laserfocusworld.org) How to measure frequency and wavelength of light?

Fourier-transform spectrometer

Fast acquisition speed, high resolution, low cost Momentum of light

The momentum of light:

Angular momentum of light? NASA

Wikipedia.com Polarization

 Linear polarization

 Circular polarization

 Elliptical polarization

 Unpolarized light

How to measure the polarization state of a light beam? Polarization

 Optical Isolators

 Imaging

 All-optical switching

 Magnetometer

 … Coherence

 Temporal coherence

 Spatial coherence

Applications: Interferometry, coherent communication, imaging (OCT)… Other light characteristics

 Spectral bandwidth (OSA)

 Average power, peak power (power meter)

 Pulse energy, repetition rate (energy meter)

 Intensity

 Divergence, beam quality (M2 measurement) Properties of Light

 Nature of light

 Velocity of light

 Frequency and wavelength

 Polarization

 Coherence

 Other light characteristics Question for thoughts

Can you come up with your own theory of light?

Why light travels at the speed that it travels?

Can we use light to propel a satellite into its orbit?

Can you come up with a better way to measure the speed of light?

Can something move faster that the speed of light? Good books to read

Book by de Broglie (1937) by and Leopold Infeld (1967)