Pulsed laser material processing with high repetition frequencies is able to initiate heat accumulation effects that can decrease processing quality even for ultrashort laser pulses. In order to gain deeper insights into these effects, a fast temperature measurement system was developed using infrared detectors and dedicated optics. The system evolved through years when responding to different challenges, like homogeneous nanosecond laser melting of metals and semiconductors or laser marking of stainless steel for corrosion resistance conservation. Appropriate calibration methods were developed for temperature evaluation from measured signal to be used in different application fields. Evaluation algorithms were invented for analyses of thermal characteristics from the signal. Hardware implementation of the analyses using field programmable gate array (FPGA) was prepared for online evaluation of heat accumulation in nanosecond time resolution during the laser micro-processing. The system was used for example for real-time analysis of thermal processes in laser surface texturing by nanosecond laser and polygon scanner for increasing adhesion of thermal spray coatings, LIPSS formation by high power multibeam picosecond laser system or processing of lithium-ion battery electrodes for enhancing charging speed. The presented diagnostics system can be applied for analysis, monitoring and control of processes in a wide range of pulsed laser applications, e.g. laser surface texturing, micromachining, polishing, drilling or 3D printing.