Unprecedented accuracy

Phys. Rev. A 87, 053411 (2013)

An accurate and reliable method for measuring extremely high laser intensities of the order of 10¹⁵ W cm⁻² has been developed by an international collaboration of scientists. David Kielpinski and co-workers say that their approach has an accuracy of within 1%, which is an order of magnitude better than existing approaches. Precise knowledge of the laser intensity in ultra-intense laser field experiments such as high harmonic generation and above-threshold ionization is important as such processes are highly nonlinear and thus very sensitive to the peak laser intensity. The scheme involves measuring the generation of photoelectrons from a hydrogen-atom beam that intersects the intense laser beam and then comparing the results with numerical solutions of the three-dimensional time-dependent Schrödinger equation. This method eliminates ambiguities and errors that usually arise from theoretical approximations. The researchers say that the scheme can be used to calibrate the peak laser intensity in any high-field experiment for which the photoelectron spectrum can be measured. As a proof of principle, they measured the intensity of a test beam from a 6.3 fs laser operating at a repetition rate of 1 kHz to be 4 × 10¹⁴ W cm⁻² with an uncertainty of just ±0.03 × 10¹⁴ W cm⁻².