QUANTUM OPTICS Tran Thi Ngoc Dung – Huynh Quang Linh – Physics A2 HCMUT 2016 Contents • Thermal Radiation • Spectral irradiance r,T, r,T, • Total irradiance R,T, • Spectral absorbance a,T, a,T[.]
Trang 1QUANTUM OPTICS
Tran Thi Ngoc Dung – Huynh Quang Linh – Physics A2 HCMUT 2016
Trang 2Contents
• Spectral irradiance r,T, r,T,
• Total irradiance R,T,
• Spectral absorbance a,T, a,T,
• Kirchhoff ‘s law of equilibrium thermal radiation
• Stefan-Boltzmann’s law
• Wien’s Displacement law
• Einstein’s Photon Theory
• Compton Effect
Trang 3THERMAL RADIATION
1 The fundamental sources of all electromagnetic radiation
2 All bodies emit electromagnetic radiation as a result of
thermal motion of their molecules; this radiation, called
thermal radiation, is a mixture of different wavelengths
Trang 4Spectral irradiance r( ,T), r( ,T)
• Consider an object of temperature of T
• The object emits electromagnetic waves
of many different frequencies
(wavelengths)
• Let dW( ,T) the energy emitted per area
dS per unit time, and transmitted by
electromagnetic waves of frequencies in
the range ( , +d )
• Spectral irradiance which is the energy
emitted per unit area per unit time per unit
frequency is defined as:
dS
dW( ,T)
T
Spectral irradiance is dependent on:
- Absolute temperature T
- Frequency
- and The nature of the object ( glass, metal )
] Hz m
W [
d dS
) T , (
dW )
T , (
Trang 5b) Total Irradiance R T
the energy emitted by a unit area of the surface per unit time and transmitted by electromagnetic waves of all
frequencies:
0 0
d ) T , ( r d
) T , ( r )
T (
Total Irradiance is dependent on :
- Absolute temperature T
- The nature of the object ( glass, metal,
balckbody )
Trang 6• Consider an object of
temperature T
• Let dW( ,T) the energy of
electromagnetic waves of
frequencies between
( , +d ) , sent to the area
dS, per unit time
• Let dW’( ,T) the energy
absorbed
• Spectral absorbance is
defined as:
) T , ( dW
) T , ( '
dW )
T , ( a
dS dW( ,T)
T
a(,T) 1
Spectral absorbance is dependent on:
- Absolute temperature T
- Frequency
- and The nature of the object ( glass, metal )
Trang 7Blackbody (Vật đen tuyệt đối)
Definition: a( ,T) =1 for all , at all T <=> Blackbody
A black body is an ideal system that absorbs all
radiation incident on it The electromagnetic radiation emitted by the black body is called blackbody radiation
A good approximation of a black body is a small hole leading to the inside of a hollow object as shown in Figure 40.1 Any radiation incident on the hole from outside the cavity enters the hole and is reflected a number of times on the interior walls of the cavity;
hence, the hole acts as a perfect absorber The nature of the radiation leaving the cavity through the hole depends only on the temperature of the cavity walls and not on the material of which the walls are made
Trang 8• Consider a thermal insulated cavity, containing
3 different objects A, B, C
• These objects radiate and absorp
electromagnetic waves
T T
T T
: state quilibrium
e thermal
At
T T
T : state initial
At
C B
A
C B
A
A
B
C
) T , ( r )
T , ( r )
T , (
r A B C
) T , ( a )
T , ( a )
T , (
a A B C
Maintaining the equilibrium state requires that an object which radiate strongly, absorps strongly
) T , (
f ) T , ( a
) T , ( r
) T , ( a
) T , ( r )
T , ( a
) T , ( r )
T , (
a
) T , (
r
C
C B
B A
“ In equilibrium thermal radiation, the ratio between spectral irradiance and spectral absorbance is not dependent on the nature of the object, it depends only on the temperature T and the given frequency Function f(,T) is called universal function or common function
KIRCHHOFF ‘S LAW
Trang 9• Applying the Kirchhoff’s law for a blackbody
• Universal function f( ,T) is the spectral irradiance of the
blackbody
) T , (
f 1
) T , ( r
) T , ( a
) T , (
Blackbody
Consequences of Kirchhoff’s law of thermal radiation
) T , ( r
) T , ( a )
T , ( f ) T , ( a )
T
,
(
) T , ( r
) T , ( r 1
) T , (
a B . B
a) Spectral irradiance of a real object is smaller than Spectral irradiance of a
blackbody
b) A real object of temperature T radiates electromagnetic wave of frequency if
this object of temp T can absorp the EM wave of frequency and the
blackbody of temperature T radiates electromagnetic wave of frequency
0 )
T , ( r and 0
) T , ( a if 0
) T , (
Trang 10O
F
T1
T2
Grating
Detector
2 The universal function f(,T)
- Has a peak
- At higher temperature, the peak of the curve moves to a higher frequency m , or a shorter wavelenth m
- The area limitted by the function f(,T) and the horizontal axis is the total irradiance of the black body