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Principiul 1 al termodinamiciiExemplu
1V T
U UdT dV pdV dQT V
2p pT T
U U V VdT dp p dT p dp dQT p T p
3p V
U UdV dp pdV dQV p
dQdTCapacitate termica =
Principiul 2 al termodinamicii
O transformare a carei singur rezultat finaleste sa transfere caldura de la un corp aflatla o anumita temperatura, la un corp aflat lao temperatura mai ridicata, este imposibila.
ENTROPIA
1
1
0
0
ni
i in
i
i i
QTQT
Ciclu reversibil
0
0 4
dQTdQT
Ciclu reversibil
5B
A
dQT 6
A
O
dQS AT
Entropia starii A
7B
A
dQS B S AT
Propietati Ale Entropiei
8
B
AB
A
dQS B S AT
dQS B S AT
Transformare reversivila
Transformare ireversivila
Transformare ireversibila intr‐un sistem izolat
09
dQS B S A
S B S A
Transformare reversibila intr‐
un sistem izolat
Sistem izolat
Principiul 3 al termodinamicii ln . (10)S k W const 231.38 10
A
Rk J KN
A
O
dQS AT
0
11A
T
dQS AT
Observatie: 0 1S W
12 lnS A k W
Calculul probabilitatii W
NU P1 2 3 4 5 6 7 8 9 107 38 11 0 9 2 20 4 4 5
1 2 .... 1 1 !
191 2 3 1 ! !
N N N N P N PR
P N P
! 20NN N
21N P
N P
N PR
N P
Tabel 1
Calculul probabilitatii W
ln ln
ln ln lnNS k W k R
k N P N P N N P P
1 ln 1 ln ln
1 ln 1 ln
NP P P PS kN N N NN N N N
U U U UkN
1 ln 1 ln 22U U U US k
Legea de deplasare a lui Wien
3
3 23Tu fc
2
3
8 24u Uc
25TU f
1 26UT f
2 31 127 28 29dS dS U Uf S fT dU dU
Derivate ale legii lui Planck
1hkT
hUe
h kT 1
1
hkT
hkT
ee
h kT
1hkT he
kT
LegeaRayleigh–Jeans
Legea lui Wien
Viteza de absorbtia si emisie
2 2 136 , 37 , ' 38spon stim em abs emR AN R BN R B N
2 1 39gN N Exp E kT Exp h kT
2 2 1' 40em emAN BN B N ' exp 1emA B
B B h kT
3 38 41
exp 1emh ch kT
3 38 ' 42A h c B si B B
Concluzii
1. Sursele termice
2. Echilibru termic la temperature camerei
1exp 1 1 43stim sponR R h kT
Laserele functioneaza prininversiunea de populatie
N2 > N1
Absorbtia si emisia in semiconductori
1
2 2
1
1 1
1 exp44
1 exp
c fc
v fv
f E E E kT
f E E E kT
2 1 emE E E
2h
Absorbtia si emisia in semiconductori ‐ 2
1 2 2 1 2, 1 47c
stim c v cv emE
R B E E f E f E dE
1 2 1 2 2, 1 48c
abs v c cv emE
R B E E f E f E dE
1 2 2 1 2, 1 46c
spon c v cvE
R A E E f E f E dE
3 2
1 2
2 3
2, 45
2r
cv g r c v c v
mE m m m m m
Jonctiune p‐n
int (53)rr rr
tot rr nr
R RR R R
, (54)rr nrrr nr
N NR R
int (55)nr
rr nr
(56)rr spon stimR R R
(57)spon nrc
NR R
1 2 (58)c nrA BN CN
LEDint int (59)P I
q
int int (60)ext ext extP P Iq
arcsin 1c n
0
1 2 sin (61)4
c
ext fT d
20 4 1 (64fT n n
21 (63)1ext n n
0 cos (64)S S
2 (65)c NA
0
int int0 0
(66) (67)qVd
e etot ext tot ext
elec
P PP V I qV
Spectrul unui LED
0 exp (69)spon g gR A E E kT
(70)2g
kTE
1.8 (71)kTh
23
34
1.8 1.38 10 30011.2
6.626*10J K K
THzJ s
Raspunsul la modulatie al LED‐ului(72)
c
dN I Ndt qV
exp (73)b m mI t I I i t
exp (74)b m mN t N N i t
(75)b c bN I qV (76)1
c mm m
m c
I qVNi
1 (77)0 1
m mm
m m c
NH
N i
3 _3 (78)
2dB opticc
f
3 _1 (79)
2dB electricc
f
Dioda LASER
•Emit puteri mari ( ~100 mW)
•Emit lumina coerenta
•Fascicolul emis are o imprastiere unghiulara mica
•Latimea spectrului este mica
•Modulatia directa a diodei laser pina la frecvente mari ( ~ 25 GHz)
Reactia si pragul LASER21 (81)
1mnRn
0 1 2 int 0exp exp exp 2 (82)E gL R R L ikL E
int int 01 2
1 1ln(83)2
2 2 2
mir
m
g EL R R
kL m sau mc nL
(84)mg g
Caracteristicile laser
•Caracteristici in unda continua
•Caracteristici de modulatie, la semnal mic
•Caracteristici de modulatie la semnal mare
•Zgomotul laserului
Caracteristicile laser in unde continua
(88)
(89)
spp
c
dP PGP Rdt
dN I N GPdt q
0v (90)g m NG g G N N
0v ,N g g TG V N N V
1intv v (91)p g cav g mir
0 0exp (92)thI T I T T
Caracteristicile P‐I a laserului
01 (93)th
thc c N p
qN qI NG
, (94)p th thP q I I I I
1 v (95)2e g mirP P
int
int
(96)2
mire th
mir
P I Iq
int
int
(97)2
e mird d
mir
dP cudI q
Eficienta cuantica externa a laserului2_ _ 2 (98)
_ _e e
extP Prata emisie fotoni q
rata injectie electroni I q I
1 (99)thext d
II
0
2 (100)etot
PV I
0 0
(101)gtot ext ext
EqV qV
Modulatia laserului
(88)
(89)
spp
c
dP PGP Rdt
dN I N GPdt q
0 1 (103)N NLG G N N P
102b m pI t I I f t
01 1 1042 c N
p
d G N Ndt
Modulatia de semnal mic
,b th m b thI I I I I sin 105p mf t t
sin 106sin 107
b m m m
b m m m
P t P p tN t N n t
exp 108b N mm m m m
R m R R m R
P G I qp p ii i
2 4 , 2 109R N b P N R P NGG P
1, 110P sp b NL b N c N bR P GP G P
Banda de modulatie
1 22 2 4 2 2 43
1 2 (112)2dB R R R R R Rf
R R 3 2 2
3 33 1132 4 4
N b NRdB b th
p
G P Gf I Iq
Zgomotul in dioda LASER
0
(115)
(116)
1 1 1172
sp Pp
Nc
c Np
dP PGP R F tdt
dN I N GP F tdt q
d G N N F tdt
2 118i j ijF t F t D t t
, 4 119PP sp spD R P D R P
Zgomotul in dioda LASER ‐ 2
2120ppC P t P t P
exp 121ppRIN C i t dt
2 2
2 22 2
2 1 2122
sp N N N c sp N
R R R R
R G P G P N R PRIN
P
2 4 , 2 123R N P N R P NGG P
1, 124R sp NL N c NR P GP G P
Latimea liniei spectrale
0exp 127EES t i d
* , exp 128EE t E t E t E t P i
2exp exp 2 129EE t i t
2
2 21 cos 3 cos 3 1302 cos2
Rsp cc R
R
R bb eP
2 2 , arctan 131R R R R Rb
21 4 132sp cR P
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