A novel phantomless, EPID‐based method of measuring the beam focal spot offset of a linear accelerator was proposed and validated for Varian machines. In this method, one set of jaws and the MLC were utilized to form a symmetric field and then a 180o collimator rotation was utilized to determine the radiation isocenter defined by the jaws and the MLC, respectively. The difference between these two isocentres is directly correlated with the beam focal spot offset of the linear accelerator. In the current work, the method has been considered for Elekta linacs. An Elekta linac with the Agility® head does not have two set of jaws, therefore, a modified method is presented making use of one set of diaphragms, the MLC and a full 360o collimator rotation. The modified method has been tested on two Elekta Synergy® linacs with Agility® heads and independently validated. A practical guide with instructions and a MATLAB ® code is attached for easy implementation.

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Experimental data comparing peak emission wavelength with organic dye laser cell length are presented. These data and knowledge of the variation of peak emission wavelength with organic dye concentration make reasonable the hypothesis that the observed effects are caused by self-absorption. A simple theory is developed on this hypothesis and the results of numerical calculations compared with the experimental data. Good agreement is obtained, but some departures from agreement suggest improvement may be expected from a time-dependent theory.

The output from a transverse-pumped organic dye laser has been investigated using time-resolved spectroscopy. It is found that for the specific case of DTTC-Iodide dissolved in either DMSO or methanol the peak wavelength in the emission band shifts during the output pulse.

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