662
23 Electricity-to-Light Conversion
(a)
(b)
(c)
(d)
(e)
Fig. 23.32 a Scheme of red laser pointer, b scheme of green laser pointer. Parts of a green laser pointer: c pump laser
diode, d YVO 4 crystal, e KTP doubler
Fig. 23.33 Population a in
thermodynamic
equilibrium T = 0 K, b
under inversion for
T = 0 K, c under inversion
for T > 0 K. Shaded areas
are populated with
electrons
D(E)
E V
E C
E
(a)
D(E)
E V
E C
E
(b)
D(E)
E V
E C
E
(c)
F n
F p
F n
F p
the quasi-Fermi levels to be larger than the band gap.
F n − F p > E g
(23.10)
The gain is defined as the (frequency-dependent) coefficient g(ω) that describes the light intensity
along a path L according to
I (L) = I (0) exp (g L) .
(23.11)
The gain spectrum as a function of the photon energy is given for non-k-conserving recombination
by (cf. (10.5) and (10.6))
g(ω) =
g
0
D e (E)D h (E
)
f e (E) f h (E
) − (1 − f e (E))(1 − f h (E
))
dE ,
(23.12)
23 Electricity-to-Light Conversion
(a)
(b)
(c)
(d)
(e)
Fig. 23.32 a Scheme of red laser pointer, b scheme of green laser pointer. Parts of a green laser pointer: c pump laser
diode, d YVO 4 crystal, e KTP doubler
Fig. 23.33 Population a in
thermodynamic
equilibrium T = 0 K, b
under inversion for
T = 0 K, c under inversion
for T > 0 K. Shaded areas
are populated with
electrons
D(E)
E V
E C
E
(a)
D(E)
E V
E C
E
(b)
D(E)
E V
E C
E
(c)
F n
F p
F n
F p
the quasi-Fermi levels to be larger than the band gap.
F n − F p > E g
(23.10)
The gain is defined as the (frequency-dependent) coefficient g(ω) that describes the light intensity
along a path L according to
I (L) = I (0) exp (g L) .
(23.11)
The gain spectrum as a function of the photon energy is given for non-k-conserving recombination
by (cf. (10.5) and (10.6))
g(ω) =
g
0
D e (E)D h (E
)
f e (E) f h (E
) − (1 − f e (E))(1 − f h (E
))
dE ,
(23.12)