“…Tunable sources near 2 μm are also of interest due to their utility in applications such as speckle-imaging [2][3], eye-safe differential absorption lidar [4][5], range finding [6], coherent Doppler wind lidar [7], and terahertz (THz) difference-frequency-generation (DFG) [8]. Wavelength generation in the 2-μm region has been achieved using Ho 3+ -doped, Tm 3+ -doped, or Tm 3+ :Ho 3+ co-doped fiber lasers [9][10], mode-locked Tm:CaYAlO4 (Tm:CYA) laser [11], near-degenerate optical parametric oscillators (OPOs) [12], and, more recently, intracavity OPOs in two-crystal walkoff compensation scheme [13]. Laser sources at ~2 μm and beyond are also necessary for pumping long-wave mid-infrared (mid-IR) OPOs and DFG sources based on non-oxide nonlinear materials such as ZnGeP2, AgGaS2, AgGaSe2 and quasi-phase-matched orientationpatterned gallium arsenide (OP-GaAs) [12,[14][15][16][17].…”