Frequency doubling in KB₅O₈4H₂O and NH₄B₅O₈4H₂O to 217.3 nm

We have produced tunable phase-matched second-harmonic radiation in a KB5O84H2O crystal between 217.3 and 234.5 nm. Phase matching was achieved by crystal rotation. We also studied frequency doubling in NH4B5O84H2O.