All-Solid-State, THz Radiation Source Using a Saturable Bragg Reflector in a Femtosecond Mode-Locked Laser

Abstract

We have demonstrated a new scheme for generating intense far-infrared or THz radiation pulses synchronously with near-infrared pulses using a saturable Bragg reflector placed inside a mode-locked laser cavity. With this newly proposed simple scheme, THz radiation which peaked at around 0.66 THz, with an average power of 2–3 nW is directly generated synchronously with femtosecond near-infrared optical pulses.

THz Radiation from Intracavity Saturable Bragg Reflector in Magnetic Field with Self-Started Mode-Locking by Strained Saturable Bragg Reflector

“…5) A saturable Bragg reflector (SBR) has been used to generate strong THz radiation in the intracavity geometry. 6) This scheme takes advantage of the higher optical peak power inside the cavity. However, it is desirable to optimize the mode-locker and intracavity THz emitter separately.…”

“…Previously, dye saturable absorbers were employed for selfstarting mode-locking in these intracavity THz-radiation generation systems. 6,7) However, the systems were bulky and relatively inconvenient to use. Recently, a new type of saturable absorber, the strained saturable Bragg reflector (SSBR), has been successfully developed for self-starting mode-locking with no focusing because of its very low saturation fluence of approximately 7 mJ/cm 2 .…”

“…With a DBR mirror with an additional λ/2 layer of Al 0.25 Ga 0.75 As. The SBR, which serves as the THz emitter 6,7) is in the other arm of the z-folded cavity as the end mirror. Its Bragg reflector consists of 24 pairs of Al 0.33 Ga 0.67 As/AlAs λ/4 layers and a top λ/4 layer of AlGaAs including a single 10-nm-thick GaAs QW.…”

“…The THz-radiation detection system is the same as that described in our previous work. 6,7) The emitted THz radiation in the transmission direction was guided by the two parabolic mirrors directly to the InSb bolometer for detecting the THzradiation power or to the Fourier-transform polarizing interferometer for measurement of the THz-radiation spectrum.…”

“…This is comparable to that obtained for the system with a dye jet as the mode-locker, 7) and is one order of magnitude larger than the previous intracavity result without a magnetic field (∼2-3 nW). 6) This indicates that a magnetic field can strongly modulate the carriers in the SBR to generate a larger amount of THz-radiation power. The quadratic dependence is the same when the polarity of the magnet is reversed.…”