Generation of picosecond ion pulses using laser-stimulated desorption from a tungsten nanotip

We present an experimental approach to the formation of sub-100 ps ion pulses at <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mn>4.5</a:mn> <a:mo>−</a:mo> <a:mn>8.5</a:mn> </a:mrow> </a:math> keV energies using laser-stimulated desorption from a tungsten nanotip at room temperature. The illumination of the tip apex with femtosecond ultraviolet laser pulses results in the ionization of adsorbed atomic and molecular species through the enhancement of a localized electric field. Unlike photoionization of atoms and molecules in the gas phase in extended volumes, determined by a typical laser focal volume, our approach naturally exploits a nanometric ionization region from tungsten nanotips with tip radii of <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mrow> <b:mn>15</b:mn> <b:mo>−</b:mo> <b:mn>150</b:mn> <b:mspace width="0.16em"/> <b:mi>nm</b:mi> </b:mrow> </b:math> and operates at a moderate optical fluence of <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mrow> <d:msup> <d:mn>10</d:mn> <d:mn>11</d:mn> </d:msup> <d:mspace width="0.16em"/> <d:mi mathvariant="normal">W</d:mi> <d:mo>/</d:mo> <d:msup> <d:mrow> <d:mi>cm</d:mi> </d:mrow> <d:mn>2</d:mn> </d:msup> </d:mrow> </d:math> . Time-of-flight measurements demonstrate stable and well-timed ion pulses. A systematic exploration of the ion pulse characteristics on laser parameters and loading gas pressures has been conducted. Our compact, yet simple, source design renders time-resolved ion-solid interaction studies practically possible, paving the way for future pump-probe studies.