#energy and threshold electrical energy
print "part (a)"
no=1.9*10**19##cm**-3##
hc=6.6*10**-34##
v=5.45*10**14##Hz
av=2##
nv=1##
n2=no/2##
eng=((n2*hc*v)/(av*nv))## J cm**-2
print "energy = %0.1f J cm**-2"%eng
print "part (b)"
oe=0.50##
mr=0.15##
lr=0.20##
teng=eng/(oe*mr*lr)##
print "threshold energy = %0.1f J cm**-2"%teng
#electrical energy is calculated wrong in the textbook
from __future__ import division
from math import log, exp
#output power
h=0.6943*10**-6##
lm=10##in cm
r1=1.0##
r2=0.8##
t1=0.98##
As=1##cm**2##
Ls=2##cm
gth=((1/(2*lm))*log((1/(r1*r2*(t1)**8))))+(As*Ls)/lm##
sg=1.5*10**-20##
ndth=gth/sg##cm**-3##
nth=ndth*As*lm##atoms
ni=5*nth##atoms
ng=1.78##
ns=2.7##
lair=2##
c=3*10**10##
trt=((2*ng*lm)/c)+((2*ns*Ls)/c)+((2*lair)/c)##seconds
npmax=((ni-nth)/2)-(nth/2)*log(ni/nth)##photons
L=14##cm
at=((As*Ls)/L)+((1/(2*L))*log(1/(r1*t1**8)))##
aext=((1/(2*L))*log(1/r2))##
tp=((trt)/(1-(r1*r2*t1**8*exp(-2*As*Ls))))##seconds
hc=6.6*10**-34##
pmax=((aext/at)*hc*c*npmax)/(h*tp)##in watts
print "maximum power = %0.2f MW"%(pmax*10**-6)
#answer is wrong in the textbook
from __future__ import division
#pulse width and spatial length
print "part (a)"
#given data :
del_v=1.5*10**9## in Hz
tau_p=1/del_v#
C=3*10**8## constant
print "pulse width,del_v = %0.2f ns"%(tau_p*10**9)
Lp=C*tau_p#
print "spatial length, Lp = %0.2f cm "%(Lp*10**2)
#spatial length is calculated wrong in the textbook
print "part (b)"
del_v=6*10**10## in Hz
tau_p=1/del_v#
C=3*10**8## constant
print "pulse width, del_v = %0.2f ps"%(tau_p*10**12)
Lp=C*tau_p*10**3#
print "spatial length, Lp = %0.2f mm"%(Lp)
#time difference
n=1.33##
x=2##
l=50##m
c=3*10**8##m/s
dt=((n*x*l)/c)##s
print "time difference is = %0.2f micro-seconds"%(dt*10**6)