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We demonstrate actively Q-switched deep ultraviolet laser operation at 261 and 320 nm by intracavity frequency doubling of an InGaN laser diode-pumped Pr:LiYF₄ laser. We obtain a maximum peak power of 61.6 W (8.7 μJ/pulse at 7.7 kHz) and 594 W (19.0 μJ/pulse at 7.7 kHz) with a pulse width of 142 and 35 ns at 261 and 320 nm, respectively. The conversion efficiency from the fundamental laser energy at 639 nm to the second-harmonic generation is 88%. Good agreement is obtained with prediction by a rate equation model.