A formidable array of advanced laser systems are emerging that produce extreme states of light and matter. By irradiating solid and gaseous targets with lasers of increasing energy densities, new physical regimes of radiation effects are being explored for the first time in the controlled laboratory setting. One result, which is being accomplished or pursued using a variety of techniques, is the realization of novel sources of x rays with unprecedented characteristics and light-matter interactions, the mechanisms of which are in many cases still being elucidated. Examples include the megajoule-class of laser-produced plasmas designed in pursuit of alternative-energy and security applications and the petawatt-class of lasers used for fast ignition and x-ray radiographic applications such as medical imaging and real-time imaging of plasma hydrodynamics. As these technologies mature, increased emphasis will need to be placed on advanced instrumentation and diagnostic metrology to characterize the spectra, time structure, and absolute brightness of x rays emitted by these unconventional sources. Such customized and absolutely calibrated measurement tools will serve as an enabling technology that can help in assessing overall system performance and progress, as well as the identification of the underlying interaction mechanisms of interest to basic and applied strong-field and high-energy-density science.