中心波长808 nm，脉宽70 fs的钛蓝宝石激光系统三倍频后产生的中心波长268 nm、带宽1.5 nm、单脉冲能量0.58 mJ的紫外超快激光光源经凹面镜聚焦后注入到样品池氩气中，由强场非线性效应诱导形成了等离子体通道，并对紫外激光脉冲光谱进行展宽。实验着重研究了268 nm波段的紫外激光成丝特点，以及在不同气体压强、聚焦长度、气体种类等条件下紫外光丝对光谱的调制作用。在2.2×10⁵ Pa氩气气压、焦距1000 mm条件下，可以获得光谱宽度3.3 nm，加宽为入射紫外脉冲的2.2倍。实验观察到压强和聚焦长度的增加都有利于等离子体通道的增加，有利于光谱展宽。紫外激光诱导的等离子体通道为在紫外波段内获得极端超快激光脉冲提供了有效的途径。

The ultrafast ultraviolet(UV) laser source with central wavelength of 268 nm, spectrum width of 1.5 nm and single pulse energy of 0.58 mJ which is obtained by third harmonic generation of Ti:sapphire laser system with pulse duration of 70 fs and central wavelength of 808 nm can generate a plasma channel due to the nonlinear effect when it is injected into Ar gas cell after focusing. We studied the filament feature of UV laser at 268 nm and the modulation of spectrum by UV filament under the condition of different gas pressure, focal length and gas category. The spectrum width of 3.3 nm can be obtained with 2.2 atm Ar pressure and 1000 mm focal length which is a factor-of-2.2 improvement compared with input spectrum. We observed that both the increase of gas pressure and focal length are beneficial to the increase of plasma channel length and spectrum broadening. The plasma channel induced by UV pulses could provide a valid approach for attaining extremely ultrafast pulses in the UV range.