In the trap chamber, the NPs first pass into a linear RF quadrupole, also operated at 106 kHz and 750 V, which can be used either as an ion guide or as a trap to accumulate NPs for later use. A final lens system allows NPs to be extracted from the linear quadrupole continuously or in pulses for injection into the main trap along its axis. The RF hexapole and quadrupole are operated to transmit species with massto-charge (M/Q) ratios in the same range that the main trap is optimized for, typically ~10 5 to ~10 6 Da/e. By filtering out atomic and molecular ions as well as NPs outside the desired M/Q range, these ion guides protect the trap and the associated optical lenses from contamination by NP or ion deposition, allowing operation for many months with no detectable surface deposits. The main trap is a cylindrically symmetric 3D quadrupole with a split-ring-electrode geometry adapted from a design by Gerlich and co-workers. Their design allowed access to the trap center along the trap axis (z) and two orthogonal radial directions (x,y), and our modified design provides two additional diagonal axes for focused laser irradiation of the trap center. The various access directions are used for NP injection, laser irradiation along two perpendicular axes, vacuum ultraviolet (VUV) irradiation, insertion of a micro-thermocouple for spectral intensity calibration, and collection of light emitted from the trap center along two perpendicular axes. The trap is operated at frequencies (F RF ) that can be varied between 10 kHz and 60 kHz, with amplitude (V 0 ) typically held near 350 V using a homemade solid state RF amplifier driven by a digital waveform generator.