### Abstract

Two methods of quantifying the spatial resolution of a camera are described, performed, and compared, with the objective of designing an imaging-system experiment for students in an undergraduate optics laboratory. With the goal of characterizing the resolution of a typical digital single-lens reflex (DSLR) camera, we motivate, introduce, and show agreement between traditional test-target contrast measurements and the technique of using Fourier analysis to obtain the modulation transfer function (MTF). The advantages and drawbacks of each method are compared. Finally, we explore the rich optical physics at work in the camera system by calculating the MTF as a function of wavelength and f-number. For example, we find that the Canon 40D demonstrates better spatial resolution at short wavelengths, in accordance with scalar diffraction theory, but is not diffraction-limited, being significantly affected by spherical aberration. The experiment and data analysis routines described here can be built and written in an undergraduate optics lab setting.

### Abstract

We report on the design, construction, and characterisation of a new class of in-vacuo optical levitation trap optimised for use in high-intensity, high-energy laser interaction experiments. The system uses a focused, vertically propagating continuous wave laser beam to capture and manipulate micro-targets by photon momentum transfer at much longer working distances than commonly used by optical tweezer systems. A high speed (10 kHz) optical imaging and signal acquisition system was implemented for tracking the levitated droplets position and dynamic behaviour under atmospheric and vacuum conditions, with ±5 μm spatial resolution. Optical trapping of 10 ± 4 μm oil droplets in vacuum was demonstrated, over timescales of >1 h at extended distances of ~40 mm from the final focusing optic. The stability of the levitated droplet was such that it would stay in alignment with a ~7 μm irradiating beam focal spot for up to 5 min without the need for re-adjustment. The performance of the trap was assessed in a series of high-intensity ($$10^{17}$$ W cm) laser experiments that measured the X-ray source size and inferred free-electron temperature of a single isolated droplet target, along with a measurement of the emitted radio-frequency pulse. These initial tests demonstrated the use of optically levitated microdroplets as a robust target platform for further high-intensity laser interaction and pointsourcestudies.

### Abstract

A popular method for generating micron-sized aerosols is to submerge ultrasonic ( *ω* ~ MHz) piezoelectric oscillators in a water bath. The submerged oscillator atomizes the fluid, creating droplets with radii proportional to the wavelength of the standing wave at the fluid surface. Classical theory for the Faraday instability predicts a parametric instability driving a capillary wave at the subharmonic (*ω*/2) frequency. For many applications it is desirable to reduce the size of the droplets; however, using higher frequency oscillators becomes impractical beyond a few MHz. Observations are presented that demonstrate that smaller droplets may also be created by increasing the driving amplitude of the oscillator, and that this effect becomes more pronounced for large driving frequencies. It is shown that these observations are consistent with a transition from droplets associated with subharmonic ( *ω*/2) capillary waves to harmonic (*ω*) capillary waves induced by larger driving frequencies and amplitudes, as predicted by a stability analysis of the capillary waves.

### Abstract

We demonstrate the operation of a device that can produce chitosan nanoparticles in a tunable size range from 50–300 nm with small size dispersion. A piezoelectric oscillator operated at megahertz frequencies is used to aerosolize a solution containing dissolved chitosan. The solvent is then evaporated from the aerosolized droplets in a heat pipe, leaving monodisperse nanoparticles to be collected. The nanoparticle size is controlled both by the concentration of the dissolved polymer and by the size of the aerosol droplets that are created. Our device can be used with any polymer or polymer/therapeutic combination that can be prepared in a homogeneous solution and vaporized.

### Thomas D. Donnelly

Student authorFaculty author

1. Calvin Leung and Thomas D. Donnelly Measuring the spatial resolution of an optical system in an undergraduate optics laboratory American Journal of Physics 85 (2017) 429-438. C. J. Price, Thomas D. Donnelly, S. Giltrap, N. H. Stuart, S. Parker, S. Patankar, H. F. Lowe, D. Drew, E. T. Gumbrell, and R. A. Smith An in-vacuo optical levitation trap for high-intensity laser interaction experiments with isolated microtargets Review of Scientific Instruments 86 (2015) 033502. Andrew P. Higginbotham, Andrew J. Bernoff, Aaron M. Guillen, Thomas D. Donnelly, and Nathan Jones Evidence of the harmonic Faraday instability in ultrasonic atomization experiments with a deep, inviscid fluid Journal of the Acoustical Society of America 130 (2011) 2694-2699. Andrew P. Higginbotham, Thomas D. Donnelly, Shenda M. Baker, and Ian K. Wright Generation of Nanoparticles of Controlled Size Using Ultrasonic Piezoelectric Oscillators in Solution ACS Applied Materials and Interfaces 2 (2010) 2360-2364. Andrew P. Higginbotham, Octavi E. Semonin, Sandra A. Bruce, Clarence W. Chan, David A. Mann, M. Maurer, W. Bang, I. V. Churina, J. Osterholz, I. Kim, T. Ditmire, and Thomas D. Donnelly Generation of Mie size microdroplet aerosols with applications in laser-driven fusion experiments Review of Scientific Instruments 80 (2009) 063503. S. Kneip, B. I. Cho, D. R. Symes, H. A. Sumeruk, G. Dyer, I. V. Churina, A. V. Belolipetski, A. Henig, O. Werhan, E. Förster, Thomas D. Donnelly, and T. Ditmire K-shell Spectroscopy of Plasmas Created by Intense Laser Irradiation of Micron-scale Cone and Sphere Targets High Energy Density Physics 4 (2008) 41-48. H. A. Sumeruk, S. Kneip, D. R. Symes, I. V. Churina, A. V. Belolipetski, Thomas D. Donnelly, and T. Ditmire Control of strong-laser-field coupling to electrons in solid targets with wavelength-scale spheres Physical Review Letters 98 (2007) 045001. H. A. Sumeruk, S. Kneip, D. R. Symes, I. V. Churina, A. V. Belolipetski, G. Dyer, J. Landry, G. Bansal, A. Bernstein, Thomas D. Donnelly, A. Karmakar, and T. Ditmire Hot electron and x-ray production from intense laser irradiation of wavelength-scale polystyrene spheres Physics of Plasmas 14 (2007) 062704. Thomas D. Donnelly, Jason M. Hogan, Andrew J. Mugler, Michael Schubmehl, Andrew J. Bernoff, S. Dasnurkar, and T. Ditmire Using ultrasonic atomization to produce an aerosol of micron-scale particles Review of Scientific Instruments 76 (2005) 113301. Thomas D. Donnelly, Jason M. Hogan, Andrew J. Mugler, Michael Schubmehl, Andrew J. Bernoff, and Bradley Forrest An experimental study of micron-scale droplet aerosols produced via ultrasonic atomization Physics of Fluids 16 (2004) 2843.