Scott R. Domingue

Differential Sputter Yields of Boron Nitride, Quartz, and Kapton Due to Low Energy Xe+ Bombardment (Preprint)

Abstract : In this contribution we present results of differential sputter yield measurements of boron nitride, quartz, and kapton due to bombardment by xenon ions. The measurements are made using a sputtering diagnostic based on a quartz crystal microbalance (QCM). The QCM measurement allows full angular resolution, i.e. differential sputtering yield measurements are measured as a function of both polar angle and azimuthal angle. Measured profiles are presented for 100, 250, 350 and 500 eV Xe+ bombardment at 0?, 15?, 30? and 45? angles of incidence. We fit the measured profiles with Modified Zhang expressions using two free parameters: the total sputter yield, Y, and characteristic energy E*. Total yields are calculated from the differential profiles and are compared with published values and weight loss values where possible.

Temporal coherence and spectral linewidth of an injection-seeded transient collisional soft x-ray laser

The temporal coherence of an injection-seeded transient 18.9 nm molybdenum soft x-ray laser was measured using a wavefront division interferometer and compared to model simulations. The seeded laser is found to have a coherence time similar to that of the unseeded amplifier, ~1 ps, but a significantly larger degree of temporal coherence. The measured coherence time for the unseeded amplifier is only a small fraction of the pulsewidth, while in the case of the seeded laser it approaches full temporal coherence. The measurements confirm that the bandwidth of the solid target amplifiers is significantly wider than that of soft x-ray lasers that use gaseous targets, an advantage for the development of sub-picosecond soft x-ray lasers.

Overcoming temporal polarization instabilities from the latent birefringence in all-normal dispersion, wave-breaking-extended nonlinear fiber supercontinuum generation.

The intrinsic weak birefringence in all-normal dispersion highly nonlinear fiber, particularly ultra-high-numerical-aperture fiber, generates supercontinuum with long term polarization instabilities, even for seed pulses launched along the perceived slow axis of the fiber. Highly co/anti-correlated fluctuations in energy between regions of power spectral density mask the extent of the spectral noise in total integrated power measurements. The instability exhibits a seed pulse power threshold above which the output polarization state of the supercontinuum seeds from noise. Eliminating this instability through the utilization of nonlinear fiber with a large designed birefringence, encourages the exploration of compression schemes and seed sources. Here, we include an analysis of the difficulties for seeding supercontinuum with the highly attractive ANDi-type lasers. Lastly, we introduce an intuitive approach for understanding supercontinuum development and evolution. By modifying the traditional characteristic dispersion and nonlinear lengths to track pulse properties within the nonlinear fiber, we find simple, descriptive handles for supercontinuum evolution.

Improved beam characteristics of solid-target soft x-ray laser amplifiers by injection seeding with high harmonic pulses

Injection seeding of solid-target soft x-ray laser amplifiers with high harmonic pulses is shown to dramatically improve the far-field laser beam profile and reduce the beam divergence. Measurements and two-dimensional simulations for a 13.9 nm nickel-like Ag amplifier show that the amplified beam divergence depends strongly on the seed and can therefore be controlled by selecting the divergence of the seed. The near-field beam size of both the seeded and unseeded lasers is shown to be determined by the size of the gain region and the divergence of the amplified beams.

Superresolved multiphoton microscopy with spatial frequency-modulated imaging

Significance Superresolution microscopy is indispensable in biological sciences. The vast majority of superresolution imaging techniques exploit real energetic states of fluorescent molecules to break the diffraction limit. To date, superresolved imaging of second- and third-harmonic generation has been limited to specific sample preparations where the polarization state of the excitation laser can be manipulated to overcome the diffraction limit. Here, we describe a method for multiphoton superresolved imaging that does not place such restrictions on the sample and allows for simultaneous superresolved imaging of both coherent and incoherent signal light. Combined with single-element detection, this technique may allow for significant advances in multimodal multiphoton imaging of highly scattering biological tissues. Superresolved far-field microscopy has emerged as a powerful tool for investigating the structure of objects with resolution well below the diffraction limit of light. Nearly all superresolution imaging techniques reported to date rely on real energy states of fluorescent molecules to circumvent the diffraction limit, preventing superresolved imaging with contrast mechanisms that occur via virtual energy states, including harmonic generation (HG). We report a superresolution technique based on spatial frequency-modulated imaging (SPIFI) that permits superresolved nonlinear microscopy with any contrast mechanism and with single-pixel detection. We show multimodal superresolved images with two-photon excited fluorescence (TPEF) and second-harmonic generation (SHG) from biological and inorganic media. Multiphoton SPIFI (MP-SPIFI) provides spatial resolution up to 2η below the diffraction limit, where η is the highest power of the nonlinear intensity response. MP-SPIFI can be used to provide enhanced resolution in optically thin media and may provide a solution for superresolved imaging deep in scattering media.

Hyperspectral imaging via labeled excitation light and background-free absorption spectroscopy

We introduce a new method of hyperspectral imaging which encodes a varying temporal intensity modulation onto the excitation (or illumination) power spectrum. Functionally, we have moved the spectrometer from the back end of an experiment to the front, where intensity modulations uniquely label wavelengths within the excitation power spectrum at different frequencies, thereby creating a temporal light label which we can identify after subsequent light–matter interactions. To demonstrate this method, we acquire two-dimensional micrographs of background-free absorption spectra by capturing the intensity modulations transferred from the excitation spectrum into the emitted fluorescent intensity. Both the temporal light labeling method and the demonstrated excitation-labeled fluorescence application are readily adaptable to hyperspectral acquisition rates far beyond the frame rates of high-speed cameras.

Nonlinear fiber amplifier with tunable transform limited pulse duration from a few 100 to sub-100-fs at watt-level powers

We report a fiber amplifier system with an output transform limited pulse duration that is broadly tunable from 400 to 60 fs. We produce <100 fs pulses with >200 kW of peak power by compensating a significant amount of third-order dispersion. The spectral noise characteristics are also investigated to insure highly stable supercontinuum generation.

Three-photon excitation source at 1250 nm generated in a dual zero dispersion wavelength nonlinear fiber

We demonstrate 1250 nm pulses generated in dual-zero dispersion photonic crystal fiber capable of three-photon excitation fluorescence microscopy. The total power conversion efficiency from the 28 fs seed pulse centered at 1075 nm to pulses at 1250 nm, including coupling losses from the nonlinear fiber, is 35%, with up to 67% power conversion efficiency of the fiber coupled light. Frequency-resolved optical gating measurements characterize 1250 nm pulses at 0.6 nJ and 2 nJ, illustrating the change in nonlinear spectral phase accumulation with pulse energy even for nonlinear fiber lengths < 50 mm. The 0.6 nJ pulse has a 26 fs duration and is the shortest nonlinear fiber derived 1250 nm pulse yet reported (to the best of our knowledge). The short pulse durations and energies make these pulses a viable route to producing light at 1250 nm for multiphoton microscopy, which we we demonstrate here, via a three-photon excitation fluorescence microscope.

Time-resolved coherent Raman spectroscopy by high-speed pump-probe delay scanning

Using a spinning window pump-probe delay scanner, we demonstrate a means of acquiring time-resolved vibrational spectra at rates up to 700 Hz. The time-dependent phase shift accumulated by the probe pulse in the presence of a coherently vibrating sample gives rise to a Raman-induced frequency shifting readily detectable in a balanced detector. This rapid delay scanning system represents a 23-fold increase in averaging speed and is >10× faster than state-of-the-art voice coil delay lines. These advancements make pump-probe spectroscopy a more practical means of imaging complex media.

General theoretical treatment of spectral modulation light-labeling spectroscopy

We theoretically derive the analytic relationship between experimental parameters and the measured incident (or illumination) optical power spectrum for a new form of spectroscopy, entitled light labeling spectroscopy. The light labeling signals are shown to arise from the interference between fields diffracted from a grating with time varying ruling density. A Gaussian model is used to illustrate the bounds of the method for recovering power spectra without artificial spectral apodization. Finally, several example systems are tabulated to give numerical insight into the possible system performances across a range of wavelength regions.