Ablation Schematic
Schematic depiction of laser ablation

The main goal of the Murray Group is to build better instruments for chemical analysis centered around laser ablation and mass spectrometry. The best way to build better instruments is to understand the chemical and physical processes behind them. We are investigating the fundamental processes of laser ablation and ionization. These include the effect of wavelength and energy on desorption, ablation and the production of ions from biological samples.

Laser Ablated Particles

Surface plot of fluence dependence of particle concentration for ablation of glycerol
Surface plot of fluence dependence of particle concentration for ablation of glycerol at wavelengths from 2.60 to 3.80 μm.

What kinds of particles are created when you shoot a sample with a laser for sampling? Creating ions? What is the sample is tissue? We use a combination of particle sizing instruments to find out. We especially like infrared lasers because they are more efficient at removing material. The trick is to make them remove material that is the most efficient for the mass spectrometry analysis that you want to do.

Fast Photography

Glycerol ablation at 2.94 μm and 3000 J/m2 fluence after (a) 10 ns, (b) 100 ns, (c) 1 μs, (d) 10 μs, (e) 24 μs, (f) 50 μs, (g) 100 μs, (h) 200 μs, (i) 500 μs, and (j) 1 ms.

In these experiments, glycerol ablation was studied using fast photography. An infrared laser was used to irradiate a droplet of glycerol and after an adjustable delay, a dye laser strobed the expanding plume. The scattered light was imaged with a high-speed CMOS camera. The time delay between the IR and UV lasers was varied from tens of nanoseconds up to a millisecond.

Fast photography: the laser hits the sample, which was illuminated by a second laser.

Sublimation Electrification

Dual vacuum chamber used to measure sublimation electrification

When exposed to vacuum, the crystals of certain organic molecules fracture and eject charged particles and clusters highly charged ions. We are using a simple apparatus to measure the charge produced by these compounds.

Recent Results

ASMS 2021: Laser Energy Stabilization for Mass Spectrometry Imaging

Lasers for matrix-assisted laser desorption ionization

Sublimation Electrification of Organic Compounds

MALDI: Past and Future: ASMS Tutorial 2017

Systematic assessment of surfactants for matrix-assisted laser desorption/ionization mass spectrometry imaging

Particle size measurement from infrared laser ablation of tissue

ASMS 2016: Systematic Assessment of Surfactants for Matrix-Assisted Laser Desorption/ Ionization Mass Spectrometry

Particle formation by infrared laser ablation of MALDI matrix compounds

Particle Production in Reflection and Transmission Mode Laser Ablation: Implications for Laserspray Ionization

Finite element simulation of infrared laser ablation for mass spectrometry

Particle Formation in Ambient MALDI Plumes

Wavelength and time-resolved imaging of material ejection in infrared matrix-assisted laser desorption