Use of a nonlinear optical crystal for generating femtosecond ultraviolet laser pulses, the use comprising: directing, at the nonlinear optical crystal , a first laser pulse from a laser source , the first laser pulse having a fundamental wavelength in a near infrared portion of the electromagnetic spectrum and having a pulse duration of less than 1000 femtoseconds, wherein the nonlinear optical crystal comprises a periodically-poled quasi-phase-matched crystal with a first portion (104-1) and a second portion (104-2) successively oriented with regard to an orientation of incident first photons of the first laser pulse , wherein the first portion (104-1) of the periodically-poled quasi-phase-matched crystal comprises a periodically poled magnesium oxide-doped stoichiometric lithium tantalate crystal and the second portion (104-2) of the periodically-poled quasi-phase-matched crystal comprises a periodically poled lanthanum barium germanium oxide crystal, wherein the first portion (104-1) of the nonlinear optical crystal receives the first photons from the first laser pulse and converts at least some of the first photons to second photons having a second harmonic wavelength of the fundamental wavelength to generate a second laser pulse , the second portion (104-2) of the nonlinear optical crystal receives at least some of the first photons and the second photons and converts at least some of the first photons and the second photons to third photons having a third harmonic wavelength of the fundamental wavelength to generate a third ultraviolet femtosecond laser pulse having the pulse duration, wherein a first cross-sectional intensity pattern of the first laser pulse matches a second cross-sectional intensity pattern of the third laser pulse , and wherein an overall thickness of the first portion (104-1) or second portion (104-2) is in a range from 100 to 1000 microns. directing, at the nonlinear optical crystal , a first laser pulse from a laser source , the first laser pulse having a fundamental wavelength in a near infrared portion of the electromagnetic spectrum and having a pulse duration of less than 1000 femtoseconds, wherein the nonlinear optical crystal comprises a periodically-poled quasi-phase-matched crystal with a first portion (104-1) and a second portion (104-2) successively oriented with regard to an orientation of incident first photons of the first laser pulse , wherein the first portion (104-1) of the periodically-poled quasi-phase-matched crystal comprises a periodically poled magnesium oxide-doped stoichiometric lithium tantalate crystal and the second portion (104-2) of the periodically-poled quasi-phase-matched crystal comprises a periodically poled lanthanum barium germanium oxide crystal, wherein the first portion (104-1) of the nonlinear optical crystal receives the first photons from the first laser pulse and converts at least some of the first photons to second photons having a second harmonic wavelength of the fundamental wavelength to generate a second laser pulse , the second portion (104-2) of the nonlinear optical crystal receives at least some of the first photons and the second photons and converts at least some of the first photons and the second photons to third photons having a third harmonic wavelength of the fundamental wavelength to generate a third ultraviolet femtosecond laser pulse having the pulse duration, wherein a first cross-sectional intensity pattern of the first laser pulse matches a second cross-sectional intensity pattern of the third laser pulse , and wherein an overall thickness of the first portion (104-1) or second portion (104-2) is in a range from 100 to 1000 microns. <EOS>