Abstract
A theoretical study for the spectral linewidth behavior of the Se X-ray laser at 206.4 angstrom has been made to obtain the intrinsic linewidth. For a Se target of 6.3 cm in length it is shown that the amplified spontaneous emission (ASE) initiates at the threshold length of z(th) = 0.13 cm. The method gives an excellent agreement with the measurements, leading to 44 m angstrom intrinsic linewidth for Se X-ray lasers at this wavelength. The calculation is also extended for another Se X-ray transition at 209.6 angstrom. We further confirm that the calculated linewidth follows a Voigt profile and its sensitivity to the collision broadening is examined. For the approach the geometrically dependent gain coefficient (GDGC) model is used. The results of the deduced gain parameters obtained from the experiment related to the target of 6.3 cm in length is used to calculate the gain profile explaining gain coefficients for samples of different excitation lengths such as 1.12 and 2.24 cm in length corresponding to the first report on the Se X-ray laser. The plot of gain coefficient versus target length for different measurements confirms that the GDGC model is able to unify Se X-ray lasers. Finally, a summary of the past reported analyses for different types of self terminating lasers will be given, where it further verifies the validity of the GDGC model to be used in different types of laser media.