The performance of mid-infrared fiber lasers operating on the 3.5 μm transition in erbium has improved significantly since the first demonstration that dual wavelength pumping allowed efficient operation. In this contribution, we will discuss the progress of fiber lasers that operate on this transition with an emphasis on advances towards short pulse generation and wavelength agility. Mode-locked operation using saturable absorption is a robust means of achieving ultra-short pulse operation in the near infrared but achieving this in the mid-infrared has been elusive. We will also describe our characterization of the mid-infrared performance of graphene, a material which has been very successfully applied to mode-locked pulse generation in the near infrared.
Short pulse operation of fiber lasers operating at wavelengths up 3 micron have been reported in recent years. At longer wavelengths, fiber lasers have only been demonstrated with a continuous operation mode. Short pulse operation in the mid-IR is necessary for utilizing such lasers in laser radars and for medical applications. Our previous numerical work suggested that Q-switching is possible on the 3.5 μm transition in erbium-doped ZBLAN in a similar manner to work demonstrated on the 2.8 μm transition in erbium. In this work we report on initial experimental results of a Q-switched, dualwavelength pumped fiber laser operating on the 3.5 μm transition in erbium-doped ZBLAN glass fibers. Using a hybrid fiber and open resonator configuration utilizing an acousto-optic modulator we demonstrated stable single pulse Q-switching while operating at repetition rates of 20 kHz and up to 120 kHz. The laser achieved a peak power of 8 W with pulse energy of 7 μJ while operating at 25 kHz. Long pulse widths on the order of 1 μs were obtained. The low peak power and long pulses are likely the result of both low gain of the transition and additional losses in the resonator which are currently being investigated. Our latest results will be presented.