A six-directional laser diode side-pumped 2.94 μ m Er:YAG solid-state laser

Abstract A six-directional laser diode (LD) side-pumped Er:YAG solid-state laser, which eschews the use of a pump reflector, is designed and experimented. The laser’s gain medium is an uncoated cylindrical 50 at.% doped Er:YAG crystal with a 3 mm diameter, side-pumped by six LDs operating at 964 nm wavelength, 100 Hz repetition rate, and 300 μ s square wave pulse width. Theoretical analysis reveals that a pump beam absorptivity exceeding 94% is obtained for a 2 mm pump beam width, while the thermal stress in the Er:YAG crystal remains below the maximum threshold of 341 MPa at the maximum total average pump power from the six LDs. Experimentally, with the cooling water temperature maintained at 19 °C to stabilize the LDs’ wavelength at 964 nm, an average output power of 20.6 W at 2.94 μ m is achieved under an average pump power of 358.8 W. Although the optical-to-optical conversion efficiency remains limited to 5.7% for using the uncoated Er:YAG crystal, this work still demonstrates the feasibility of enhancing the 2.94 μ m laser power through side-pumped with more than three LDs.