Femtosecond laser pulses are far too brief for any electronic instrument to measure, so physicists characterise them optically, usually by stitching together several scanned measurements. Existing single-shot techniques struggle with the longer pulses that dominate industrial and medical applications. Researchers in the Atomic Physics division at Lund University, including doctoral student Daniel Díaz Rivas and senior lecturer Cord Arnold, have found an elegant workaround, published in the journal Optica.
Their method sends the laser beam through a diffraction grating and images the grating with lenses, so that different parts of the beam are stretched in time by controlled, spatially varying amounts. The compact arrangement lengthens femtosecond pulses more than tenfold and allows a pulse to be fully characterised from one single shot, without pre-compensation optics. The approach covers durations from a few femtoseconds to hundreds, and was developed with the company Sphere Ultrafast Photonics, supported by the European Innovation Council.
Standard tools often yield only an estimate of pulse duration, whereas single-shot characterisation captures each individual pulse, opening the door to real-time monitoring of lasers used in eye surgery and industrial micro-machining, where pulse quality translates directly into precision. The team also notes that the same optical principle could be used in reverse, to sculpt the spatiotemporal properties of light pulses, a capability of growing interest for studies of light-matter interaction.