Broad spectrum pulse generation in multi-component continuum generators

Broad Spectrum Pulse Generation in Multi-component Continuum Generators Dainius Kučinskas Femtosecond few-cycle laser pulses are used in many modern scientific experiments and practical applications. They require a broad spectrum, which is often generated in one few-mm thick plate of nonlinear medium, but this method limits the continuum pulse energy to a few µJ. In this work we have investigated a recently proposed method of multi-plate continuum generation, using thin plates of sapphire and fused silica. A system for measuring and characterising the generated continuum pulses was developed, including a cross-correlation frequency-resolved optical gating (XFROG) setup to fully describe the phase and amplitude of the pulse. Three different laser sources were used for continuum generation, with central wavelengths from 800nm to 1.5µm. It was observed that continua with the broadest spectrum, coherent phase and orderly beam profile can be generated adhering to the optimal plate entrance beam intensity. This ensures the maximum broadening of the spectrum, while avoiding multiple filamentation. This criterion can be empirically met by finding the correct distances between the plates using direct spectral, beam profile and XFROG measurements of the continuum. A 68µJ continuum pulse with a wavelength range of 570-1100nm above the spectral energy density value of 10 nm/nJ was generated using a 800nm, 138µJ pump pulse. A 63µJ continuum pulse with wavelengths extending from 715nm to at least 1100nm above 1 nJ/nm was produced using a 1030nm, 180µJ pump pulse. A 177µJ continuum pulse with an octave-spanning wavelength range of 980-1910nm exceeding 10 nJ/nm, coherent spectral phase and a transformlimited length of 5 fs was generated using a 1500nm, 250µJ pump pulse. By compressing the pulse to a Fourier-limited duration, we can hope to generate monocyclic pulses. The use of thinner plates led to a spectrum covering 570-1970nm above 10 nJ/nm and a pulse energy of 270µJ. In each case, the resulting values of spectral energy density exceed up to thousands of times those reported in literature by generating a single filament in solid media