Ferroferric-Oxide Nanoparticle Based Optical Modulator for $2~\mu$ m Spectral Region

By transferring the colloidal suspensions of ferroferric-oxide (Fe ₃ O ₄ ) nanoparticles (FONPs) onto a quartz plate, zero-dimension FONPs saturable absorber (SA) is successfully fabricated and employed in a Tm:Lu ₃ Al ₅ O ₁₂ (Tm:LuAG) bulk laser. The properties of the FONPs-SA including Raman response, nonlinear optical response, and broad-band spectral absorption from 1800 nm to 2500 nm are measured. With the as-prepared FONPs-SA, laser pulses with the shortest duration of 600 ns, a maximum repetition rate of 96 kHz and maximum pulse energy of $4.9~\mu \text{J}$ are obtained, corresponding to a maximum peak power of 8.2 W. This is the first experimental demonstration of the zero-dimension FONPs-SA as Q-switch in $2~\mu \text{m}$ spectral region and even longer wavelength mid-infrared spectral region, to the best of our knowledge, which indicates that the zero-dimension FONPs-SA can act as a promising optical modulator in mid-infrared spectral region.