Coherent emission from Ho3+ions by pumping into the YIG absorption band

Coherent emission from Ho3+ ions (2.1 μm) in a YIG host at 77 °K has been observed by optical pumping into the electronic absorption bands of the YIG host material, using (i) a pulsed Nd : glass laser to pump into the tail of the 6A1g→4T1g band (which has an absorption coefficient α=0.18 cm−1 at 1.06 μm) or (ii) a pulsed ruby laser (0.6943 μm) to pump the 6A1g→4T2g band near its peak (where α=300 cm−1). The Ho3+ emission from an illuminated slab 30–40 μm was investigated as a function of input pump energy. The electronic absorption bands of YIG are strong, broad, and have good energy‐transfer efficiency to the upper laser level of the Ho3+ ions.