A fast microchannel plate-scintillator detector for velocity map imaging and imaging mass spectrometry

A versatile and transportable endstation for controlled molecule experiments

We report on a new versatile transportable endstation for controlled molecule (eCOMO) experiments providing a combination of molecular beam purification by electrostatic deflection and simultaneous ion and electron detection using velocity-map imaging (VMI). The b-type electrostatic deflector provides spatial dispersion of species based on their effective-dipole-moment-to-mass ratio. This enables selective investigation of molecular rotational quantum states, conformers, and molecular clusters. Furthermore, the double-sided VMI spectrometer equipped with two high-temporal-resolution event-driven Timepix3 cameras provides detection of all generated ions independently of their mass-over-charge ratio and electrons. To demonstrate the potential of this novel apparatus, we present experimental results from our investigation of carbonyl sulfide (OCS) after ionization. In particular, we provide the characterization of the molecular beam, electrostatic deflector, and electron- and ion-VMI spectrometer. The eCOMO endstation delivers a platform for ultrafast dynamics studies using a wide range of light sources from table-top lasers to free-electron-laser and synchrotron-radiation facilities. This makes it suitable for research activities spanning from atomic, molecular, and cluster physics, over energy science and chemistry, to structural biology.

Slicing Newton spheres with a two-camera 3D imaging system

We demonstrate a simple approach to achieve three-dimensional ion momentum imaging. The method employs two complementary metal-oxide-semiconductor cameras in addition to a standard microchannel plates/phosphor screen imaging detector. The two cameras are timed to measure the decay of luminescence excited by ion hits to extract the time of flight. The achieved time resolution is better than 10 ns, which is mainly limited by camera jitters. A better than 5 ns resolution can be achieved when the jitter is suppressed.

Time-Resolved Imaging of High Mass Proteins and Metastable Fragments Using Matrix-Assisted Laser Desorption/Ionization, Axial Time-of-Flight Mass Spectrometry, and TPX3CAM

The Timepix (TPX) is a position- and time-sensitive pixelated charge detector that can be coupled with time-of-flight mass spectrometry (TOF MS) in combination with microchannel plates (MCPs) for the spatially and temporally resolved detection of biomolecules. Earlier generation TPX detectors used in previous studies were limited by a moderate time resolution (at best 10 ns) and single-stop detection for each pixel that hampered the detection of ions with high mass-to-charge (m/z) values at high pixel occupancies. In this study, we have coupled an MCP-phosphor screen-TPX3CAM detection assembly that contains a silicon-coated TPX3 chip to a matrix-assisted laser desorption/ionization (MALDI)-axial TOF MS. A time resolution of 1.5625 ns, per-pixel multihit functionality, simultaneous measurement of TOF and time-over-threshold (TOT) values, and kHz readout rates of the TPX3 extended the m/z detection range of the TPX detector family. The detection of singly charged intact Immunoglobulin M ions of m/z value approaching 1 × 10⁶ Da has been demonstrated. We also discuss the utilization of additional information on impact coordinates and TOT provided by the TPX3 compared to conventional MS detectors for the enhancement of the quality of the mass spectrum in terms of signal-to-noise (S/N) ratio. We show how the reduced dead time and event-based readout in TPX3 compared to the TPX improves the sensitivity of high m/z detection in both low and high mass measurements (m/z range: 757-970,000 Da). We further exploit the imaging capabilities of the TPX3 detector for the spatial and temporal separation of neutral fragments generated by metastable decay at different locations along the field-free flight region by simultaneous application of deflection and retarding fields.

Ion Microscope Imaging Mass Spectrometry Using a Timepix3-Based Optical Camera

Ion microscopy allows for high-throughput mass spectrometry imaging. In order to resolve congested mass spectra, a high degree of timing precision is required from the microscope detector. In this paper we present an ion microscope mass spectrometer that uses a Timepix3 hybrid pixel readout with an optimal 1.56 ns resolution. A novel triggering technique is also employed to remove the need for an external time-to-digital converter (TDC) and allow the experiment to be performed using a low-cost and commercially available readout system. Results obtained from samples of rhodamine B demonstrate the application of multimass imaging sensors for microscope mass spectrometry imaging with high mass resolution.

All-Optical Three-Dimensional Electron Momentum Imaging

We report a new implementation of three-dimensional (3D) momentum imaging for electrons, employing a two-dimensional (2D) imaging detector and a silicon photomultiplier tube (siPMT). To achieve the necessary time resolution for 3D electron imaging, a poly(p-phenylene)-dye-based fast scintillator (Exalite 404) was used in the imaging detector instead of conventional phosphors. The system demonstrated an electron time-of-flight resolution comparable with that of electrical MCP pick-off (tens of picoseconds), while achieving an unprecedented dead time reduction (∼0.48 ns) when detecting two electrons.

Fast camera spatial characterization of photonic polarization entanglement

Scalable technologies to characterize the performance of quantum devices are crucial to creating large quantum networks and quantum processing units. Chief among the resources of quantum information processing is entanglement. Here we describe the full temporal and spatial characterization of polarization-entangled photons produced by Spontaneous Parametric Down Conversions using an intensified high-speed optical camera, Tpx3Cam. This novel technique allows for precise determination of Bell inequality parameters with minimal technical overhead, and for new characterization methods for the spatial distribution of entangled quantum information. The fast-optical camera could lead to multiple applications in Quantum Information Science, opening new perspectives for the scalability of quantum experiments.

Microscope imaging mass spectrometry with a reflectron

A time-of-flight microscope imaging mass spectrometer incorporating a reflectron was used to image mass-resolved ions generated from a 270 μm diameter surface. Mass and spatial resolutions of 8100 ± 700 m/Δm and 18 μm ± 6 μm, respectively, were obtained simultaneously by using pulsed extraction differential acceleration ion optical focusing to create a pseudo-source plane for a single-stage gridless reflectron. The obtainable mass resolution was limited only by the response time of the position-sensitive detector and, according to simulations, could potentially reach 30 200 ± 2900 m/Δm. The spatial resolution can be further improved at the expense of the mass resolution to at least 6 μm by increasing the applied extraction field. An event-triggered fast imaging sensor was additionally used to record ion images for each time-of-flight peak resolved during an experimental cycle, demonstrating the high-throughput capability of the instrument.

Invited Review Article: Photofragment imaging

Photodissociation studies in molecular beams that employ position-sensitive particle detection to map product recoil velocities emerged thirty years ago and continue to evolve with new laser and detector technologies. These powerful methods allow application of tunable laser detection of single product quantum states, simultaneous measurement of velocity and angular momentum polarization, measurement of joint product state distributions for the detected and undetected products, coincident detection of multiple product channels, and application to radicals and ions as well as closed-shell molecules. These studies have permitted deep investigation of photochemical dynamics for a broad range of systems, revealed new reaction mechanisms, and addressed problems of practical importance in atmospheric, combustion, and interstellar chemistry. This review presents an historical overview, a detailed technical account of the range of methods employed, and selected experimental highlights illustrating the capabilities of the method.

Coincidence velocity map imaging using Tpx3Cam, a time stamping optical camera with 1.5 ns timing resolution

We demonstrate a coincidence velocity map imaging apparatus equipped with a novel time-stamping fast optical camera, Tpx3Cam, whose high sensitivity and nanosecond timing resolution allow for simultaneous position and time-of-flight detection. This single detector design is simple, flexible, and capable of highly differential measurements. We show detailed characterization of the camera and its application in strong field ionization experiments.

Three-dimensional imaging of carbonyl sulfide and ethyl iodide photodissociation using the pixel imaging mass spectrometry camera

The Pixel Imaging Mass Spectrometry (PImMS) camera is used in proof-of-principle three-dimensional imaging experiments on the photodissociation of carbonyl sulfide and ethyl iodide at wavelengths around 230 nm and 245 nm, respectively. Coupling the PImMS camera with DC-sliced velocity-map imaging allows the complete three-dimensional Newton sphere of photofragment ions to be recorded on each laser pump-probe cycle with a timing precision of 12.5 ns, yielding velocity resolutions along the time-of-flight axis of around 6%-9% in the applications presented.

Coincidence ion imaging with a fast frame camera

A new time- and position-sensitive particle detection system based on a fast frame CMOS (complementary metal-oxide semiconductors) camera is developed for coincidence ion imaging. The system is composed of four major components: a conventional microchannel plate/phosphor screen ion imager, a fast frame CMOS camera, a single anode photomultiplier tube (PMT), and a high-speed digitizer. The system collects the positional information of ions from a fast frame camera through real-time centroiding while the arrival times are obtained from the timing signal of a PMT processed by a high-speed digitizer. Multi-hit capability is achieved by correlating the intensity of ion spots on each camera frame with the peak heights on the corresponding time-of-flight spectrum of a PMT. Efficient computer algorithms are developed to process camera frames and digitizer traces in real-time at 1 kHz laser repetition rate. We demonstrate the capability of this system by detecting a momentum-matched co-fragments pair (methyl and iodine cations) produced from strong field dissociative double ionization of methyl iodide.

Modifications to a commercially available linear mass spectrometer for mass-resolved microscopy with the pixel imaging mass spectrometry (PImMS) camera

RATIONALE

Imaging mass spectrometry is a powerful analytical technique capable of accessing a large volume of spatially resolved, chemical data from two-dimensional samples. Probing the entire surface of a sample simultaneously requires a detector with high spatial and temporal resolutions, and the ability to observe events relating to different mass-to-charge ratios.

METHODS

A commercially available time-of-flight mass spectrometer, designed for matrix-assisted laser desorption/ionization (MALDI) analysis, was combined with the novel pixel imaging mass spectrometry (PImMS) camera in order to perform multi-mass, microscope-mode imaging experiments. A number of minor modifications were made to the spectrometer hardware and ion optics so that spatial imaging was achieved for a number of small molecules.

RESULTS

It was shown that a peak width of Δm50 %  <  1  m/z unit across the range 200 ≤ m/z  ≤  800 can be obtained while also achieving an optimum spatial resolution of 25 µm. It was further shown that these data were obtained simultaneously for all analytes present without the need to scan the experimental parameters.

CONCLUSIONS

This work demonstrates the capability of multi-mass, microscope-mode imaging to reduce the acquisition time of spatially distributed analytes such as multi-arrays or biological tissue sections. It also shows that such an instrument can be commissioned by effecting relatively minor modifications to a conventional commercial machine.