terahertz generation by the beating of two laser beams in collisional plasmas ram kishor singh and...
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Terahertz generation by the beating of two laser beams in collisional plasmas
Ram Kishor Singh and R. P. SharmaCentre for Energy Studies, Indian Institute of Technology Delhi, India
...
The wave equations for the laser beams can be written as
Considering the solution as follows
The spatial profile of intensity distribution of laser beams can be written as,
The dielectric function can be written as,
In the steady state:the thermal pressure induced by the laser beams is balanced by the space charge force.
j j2j j 2 2
J E4 1E .E
c t c t
j j0 j j j jˆE r, z xA r, z exp i k z t ik S r, z
22
2 j0 'j0 j2
j0 jj
E rA r, z exp 2K z
r ff
2
jj
j
dfrS r, z z
2f dz
eff j0 j j ijE .E i
*0 1 .e j j j
j
T T A A
2
2 203j
e B j
e M
m k T
12
00
0
2s
ee
Tn n
T T
2 ' 2 ' 2 ' 2 '2 21 10 1 2 20 2 1 10 1 2 20 2
32 2 4 2 4 2 2 22 40 1 10 2 20 1 20
1 1exp 2 exp 2 exp 2 exp 21 2 2exp
2 2j p j
j jj j j
s sE K z E K z E K z E K zd f f
dz f r f r f fk r f
j ij'j
j0
k1K
2
From the equation of motion
The energy balance equation
The electron temperature at beat wave frequency
The THz wave propagation equation
The nonlinear current density
THz amplitude variation with respect to propagation direction
'e e
dvm eE m v
dt
B e e B e 0 0
d 3 3k T n J.E k T T n
dt 2 2
2 2e
1 2 1 22 20 e 1 B 0 e 2 B 0
T e eE .E E .E
T 6m k T 6m k T
l nlT T
TT T. .
2 J J1 E 42E E2 2 2 tc t c
2q p' dc 1 10 20 2 10 20
T T0 2T 0 1 2 1 2
2' '1 22 2 2 2
10 1 20 2
ni E s E .E E .EK E
z 4k n c 2 f f f f
r 1 1exp K K z
2 r f r f
nl
iqz 0 dTq 1 1 2 2 1 2
s v eJ 1n e E .E E .E
t 2 2
,
,
,
,
2
j j0 j j2j0
ri k z t
2rE x E exp
s
2j ej j0 0
0
Tk ,
c T
dc
de 0
eEv
m
iqzn n n eq0
T TT T0
i k z txE E e
10 1ns
10.5dcE kVcm
11dcE kVcm
10 1ns
10.5dcE kVcm
11dcE kVcm
10 1.3ps
AbstractThe role of two cross-focused spatial-Gaussian laser beams has been studied for the high power and efficient terahertz (THz) radiation generation in the collisional plasma. The nonlinear current at THz frequency arises on account of temperature dependent collision frequency of electrons with ions in the plasma and the presence of a static electric field (applied externally in the plasma) and density ripple. Optimisation of laser-plasma parameters gives the radiated THz power of the order of 4
010 P .
Conclusions:
The cross focused laser beams in collisional plasmas are able to enhance the generation of THz radiation in the presence of external transverse static electric field. The maximum amplitude of THz radiation generation can be achieved by the suitable phase matching condition with the employment of ripple density. Amplitude of the generated THz radiation increased by factor of two to three in the case of cross-focusing of two Gaussian beams as compared to the case without cross-focusing.
Acknowledgement: University Grant Commission (UGC), India.
141 1.96 10 rad / s
142 1.78 10 rad / s
13p 1.7 10 rad / s q 0n 0.3n
9 21 2I I 1 10 W / cm
10 20r r 40 m
s 3
12 2pT2T
q 1 1c
12 2
T PT 2
T
k 1c
2p' 0
T 2T T
K2 c k
T 1 2k k k q
References:R. P. Sharma and R. K. Singh, Phys. Plasmas, 21, 073101 (2014).A. Houard, Y. Liu, B. Prade, V. T. Tikhonchuk, and A. Mysyrowicz, Phys. Rev. Lett., 100, 255006 (2008).M. S. Sodha, A. K. Ghatak, and V. K. Tripathi, Prog. Opt., 13, 169 (1976)S. A. Akhmanov, A. P. Sukhorukov, and R. V. Khokhlov, Sov. Phys. Usp., 10, 609(1968).
10 1.3ps
10 1ns