Mass spectrometer with a laser system (500; 600; 900; 1000) for the ionization of a sample (521; 621; 921, 1021) by matrix-assisted laser desorption in mass spectrometric analysis, characterized in that the laser system (500; 600; 900; 1000) contains, outside the laser medium, a device that increases the spatial modulation of a laser beam (602; 902; 1002), and a partially or fully adjustable intensity distribution of the laser radiation at the location of the sample (521; 621; 921, 1021) from a plurality of intensity peaks (522; 101-108) or a plurality of intensity cutters or a mixture of both, wherein an intensity cut is defined as a line-shaped intensity distribution at which the intensity on the line has a maximum in at least one direction, and wherein the means for increasing the spatial modulation of the laser beam (602; 902; 1002) includes: (i) a transparent plastic sheet e (603), which has different thicknesses at different points, so that the spatial modulation of the phase in the beam profile of the laser beam is increased, (ii) a multimode fiber (503) whose length is chosen such that the temporal coherence of the laser radiation is greater than is the transit time difference of the transverse fiber modes, so that the intensity distribution at the fiber output (504) no longer results from the superimposition of the intensities of the transverse fiber modes, but from the interference of the electromagnetic fields of the individual fiber modes, and their fiber output (504) via a lens (504) 505) and a deflecting mirror (506) is imaged onto the sample, (iii) a lens field (903) whose lenses produce at the position of a diaphragm (904) individual spatially separated foci, which are defined by a further lens (905) and a deflecting mirror (905). 906) can be imaged in a reduced manner onto the sample (921), or (iv) a diffractive optical element (1003) designed as a DOE, which spatially diffracts hey modulation of both the intensity and the phase in the beam profile of the laser beam (1002) can increase.
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