Ultraviolet　laser　has　high　frequency,　short　wavelength,　large　single-photon　energy,　and　high　spatial　resolution,　and　has　wide　applications　in　many　fields　such　as　fine　processing,　life　sciences,　and　spectroscopy.　In　this　work,　a　wavelength　tunable　ultraviolet　laser　based　on　intracavity　third　harmonic　generation　from　an　external-cavity　surface-emitting　laser　is　reported.　The　W-type　resonant　cavity　of　the　laser　is　composed　of　a　distributed　Bragg　reflector　(DBR)　at　the　bottom　of　the　gain　chip,　three　plane-concave　mirrors,　and　a　rear　plane　mirror.　On　the　arm　containing　the　gain　chip,　a　birefringent　filter　is　inserted　at　the　Brewster　angle　as　the　polarization　and　wavelength　tuning　element,　which　can　also　narrow　the　linewidth　of　the　fundamental　laser　to　a　certain　extent.　A　type-I　phase-matched　LBO　crystal　is　placed　on　the　beam　waist　between　the　folding　mirrors　M2　and　M3　to　convert　the　980　nm　fundamental　laser　into　490　nm　blue　light,　and　a　type-I　phase-matched　BBO　crystal　is　inserted　in　the　beam　waist　near　the　rear　mirror　to　produce　a　327　nm　ultraviolet　output　from　the　remained　980　nm　fundamental　laser　and　the　frequency-doubled　490　nm　second　harmonic.　Before　the　BBO　crystal,　a　half-wave　plate　at　980　nm　is　employed　to　change　the　polarization　of　the　fundamental　laser,　so　as　to　meet　the　type-I　phase-matching　condition　of　the　used　BBO　crystal.　Owing　to　the　larger　nonlinear　coefficient　of　the　type-I　phase-matched　BBO　crystal,　and　its　obviously　higher　transmittance　at　327　nm　wavelength　than　the　usually　used　LBO　crystal,　the　output　power　is　obtained　to　be　538　mW　at　327　nm　ultraviolet　wavelength,　corresponding　to　a　conversion　efficiency　of　1.1%　from　pump　light　to　ultraviolet　laser.　The　experiment　is　performed　under　conditions　of　15　℃　temperature,　47　W　absorbed　pump　power,　5　mm-length　LBO　and　5　mm-length　BBO　crystals.　By　using　a　2　mm-thick　birefringent　filter　as　the　tuning　element,　34.1　nm　tuning　range　of　the　980　nm　fundamental　laser,　14.3　nm　tuning　range　of　the　490　nm　second　harmonic,　and　8.6　nm　tuning　range　of　the　327　nm　third　harmonic　are　obtained.　The　ultraviolet　laser　exhibits　good　beam　quality　as　well　as　acceptable　power　stability　with　the　maximum　power　fluctuation　less　than　2%　within　4.5　h.　©　2024　Chinese　Physical　Society.