Use of a nonlinear optical crystal for generating femtosecond ultraviolet laser pulses, the use comprising: focusing, by means of a focusing element and 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 has a first portion and a second portion successively oriented with regard to an orientation of incident first photons of the first laser pulse, wherein: the first portion 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 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 aser pulse having the pulse duration; wherein the nonlinear optical crystal comprises a periodically-poled quasi-phase-matched crystal, wherein the periodically-poled quasi-phase-matched crystal is used so that the first photons from the first laser pulse, the second photons from the second laser pulse and the third photons from the third laser pulse collinearly travel through the periodically-poled quasi-phase-matched crystal; wherein the first portion of the nonlinear optical crystal and the second portion of the nonlinear optical crystal are formed as a single unitary material; wherein an overall thickness of the first portion or second portion is in a range from 100 to 1000 microns; and wherein a first cross-sectional intensity pattern of the first laser pulse matches a second cross-sectional intensity pattern of the third laser pulse. focusing, by means of a focusing element and 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 has a first portion and a second portion successively oriented with regard to an orientation of incident first photons of the first laser pulse, wherein: the first portion 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 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 aser pulse having the pulse duration; wherein the nonlinear optical crystal comprises a periodically-poled quasi-phase-matched crystal, wherein the periodically-poled quasi-phase-matched crystal is used so that the first photons from the first laser pulse, the second photons from the second laser pulse and the third photons from the third laser pulse collinearly travel through the periodically-poled quasi-phase-matched crystal; wherein the first portion of the nonlinear optical crystal and the second portion of the nonlinear optical crystal are formed as a single unitary material; wherein an overall thickness of the first portion or second portion is in a range from 100 to 1000 microns; and wherein a first cross-sectional intensity pattern of the first laser pulse matches a second cross-sectional intensity pattern of the third laser pulse. the first portion 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 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 aser pulse having the pulse duration; wherein the nonlinear optical crystal comprises a periodically-poled quasi-phase-matched crystal, wherein the periodically-poled quasi-phase-matched crystal is used so that the first photons from the first laser pulse, the second photons from the second laser pulse and the third photons from the third laser pulse collinearly travel through the periodically-poled quasi-phase-matched crystal; wherein the first portion of the nonlinear optical crystal and the second portion of the nonlinear optical crystal are formed as a single unitary material; wherein an overall thickness of the first portion or second portion is in a range from 100 to 1000 microns; and wherein a first cross-sectional intensity pattern of the first laser pulse matches a second cross-sectional intensity pattern of the third laser pulse.