A detector system has been developed for the soft x-ray and extreme UV ranges. It is called DUVEX and has been
designed in order to be easy to implement and use, and cheap to operate. It consists in a YAG:Ce scintillator coupled to a
photomultiplier module working in the counting mode. The system can be operated under vacuum. We report on the
design and the performances of this detector in terms of response, noise, stability and efficiency. Soft x-ray spectra of
different elements (from B to W) obtained in the wavelength dispersive mode acquitted with DUVEX are presented.
The availability of high power semiconductor lasers makes it possible to optically pump large area cavities with a good spatial homogeneity and with an arbitrary profile, which is otherwise difficult to obtain with electrical injection. In addition, a high pumping efficiency may be obtained with reduced heat generation thanks to the absence of Joule heating. However, in order to fully benefit from these advantages it is necessary to pay special attention to the spectral characteristics of the cavity and to design it accordingly. We present and extend a Bragg mirrors optimization technique to control both the absorption and the transmission of the cavity around the pump wavelength. The absorption coefficient reaches close to 80% over a 30nm width pumping window around 800nm while keeping the cavity transmission below 10% at the pump wavelength. Laser action is obtained at 890 nm with an almost flat pumping (and hence gain) profile over a diameter of 80μm and a laser threshold of 11.5kW/cm<sup>2</sup>. We point out that the method may be employed in the design of vertical external cavity surface emitting lasers.