Tata Institute develops new method to measure high power, ultrashort laser pulses

06 Aug 2024

Partnership with Sweden’s Umeå University uses spectral interferometry to sample at different points simultaneously.

The Tata Institute of Fundamental Research (TIFR), Mumbai, India, has developed a new method to measure ultrahigh power, ultrashort laser pulses in a comprehensive manner.

The paper reporting this, entitled “Single-shot, spatio-temporal analysis of relativistic plasma optics”, has been published in Optica.

Measuring the temporal shape of such pulses is challenging; for one, the time distortions that a short pulse suffers whenever it passes through a medium. The larger the power, the more severe these distortions. Another major complication concerns the pulse time profile being different at different points within the laser beam itself.

Most often, scientists may not bother about these variations across the beam spatial extent and assume a single temporal profile. However, the larger the beam and/or the more the length it traverses in a medium, the more critical these distortions become, which can significantly change the pulse shape. At ultrahigh peak powers it is imperative to know what the time duration is at different points across the spatial extent of the beam.

Spectral interferometry

The TIFR team used a specially-designed instrument to measure the time profiles across spatial points in the ultrashort laser beam. They employed spectral interferometry at different spatial locations across the beam simultaneously, to achieve this. The team collaborated with Umeå University, Sweden, on this study.

The TIFR team commented, “With the scientific world marching towards peak laser powers never imagined before – trillions of watts, in laser beams spread over diameters of several tens of centimeters – this method will not only be extremely useful but essential.”

The TIFR statement added, there another boost for the new method. These ultrahigh power lasers emit pulses every once in a while – once over many seconds, minutes, or hours. The earlier techniques of measurement needed to sample multiple pulses before estimating the pulse profile, which could be cumbersome. The TIFR advance solves this problem – because it works for a single pulse.”

As laser peak powers continue to increase, conventional solid optical components may not be able to handle them as they can breakdown by ionization. The technology is therefore moving towards using ionized matter or plasma itself, to design these optical components.

Such plasmas can be highly unstable and cause further distortions in the spatio-temporal profiles of the pulse incident on them. However, TIFR says, its new method is “perfectly suited to measure these distortions”.