Ultrafast THz nonlinear optics: saturable absorption of THz signals in doped semiconductors
Prof. Dr. Dmitry Turchinovich
Doped or photoexcited semiconductors are good absorbers of THz radiation, and THz absorption is roughly proportional to material conductivity.
The conductivity of an n-doped semiconductor can be reduced by carrier-heating and Gunn effect in externally-applied electric field. The electrons will accelerate in the applied electric field and will occupy the high-momentum, large effective mass states in E(k) space, thus reducing their mobility.
Here, the carrier-heating and Gunn effects in n-doped semiconductors are induced by the electric field of the propagating THz pulse, which consequently leads to its saturable absorption in the material.
|Fig. 1.||Redistribution of conduction-band electron population in GaAs due to carrier-heating.|
|Fig. 2.||Strong-field THz pulse and its amplitude spectrum.|
|Fig. 3.||(a,c,e) amplitude and (b,d,f) power transmission coefficients as a function of peak THz electric field and THz pulse fluence, respectively, in three parabolic-band n-doped bulk semiconductors: GaAs, GaP, and Ge. Solid lines – fits to a standard saturable transmission function. Fit parameters are indicated in Figure.|
|Fig. 4.||THz pulse dynamics as a result of propagation through a saturable absorber: (a) THz pulse shortening, and (b) group delay increase|
M.C. Hoffmann and D. Turchinovich
"Semiconductor saturable absorbers for ultrafast terahertz signals"
Appl. Phys. Lett. 96, 151110 (2010)