With the development of semiconductor industry, manufacture of large-scale integrated circuits places increasing requirement on photolithography technology. Excimer laser devices as light sources of photolithography are crucial to improvement of the photolithography technology. It is desired that the excimer laser devices have both a narrow line-width and high power output. However, a conventional combination of a laser and a line-width narrowing module narrows down the line-width by sacrificing the power output. Therefore, in order to achieve both the narrow line-width and the high power output, the power output and the line-width of a laser device has to be adjusted properly so as to obtain an excimer laser to meet special requirements (for example, suitable for use as a photolithography light source).