Bryan D. Moran

Multiscale metallic metamaterials.

Materials with three-dimensional micro- and nanoarchitectures exhibit many beneficial mechanical, energy conversion and optical properties. However, these three-dimensional microarchitectures are significantly limited by their scalability. Efforts have only been successful only in demonstrating overall structure sizes of hundreds of micrometres, or contain size-scale gaps of several orders of magnitude. This results in degraded mechanical properties at the macroscale. Here we demonstrate hierarchical metamaterials with disparate three-dimensional features spanning seven orders of magnitude, from nanometres to centimetres. At the macroscale they achieve high tensile elasticity (>20%) not found in their brittle-like metallic constituents, and a near-constant specific strength. Creation of these materials is enabled by a high-resolution, large-area additive manufacturing technique with scalability not achievable by two-photon polymerization or traditional stereolithography. With overall part sizes approaching tens of centimetres, these unique nanostructured metamaterials might find use in a broad array of applications.

532-nm laser sources based on intracavity frequency doubling of extended-cavity surface-emitting diode lasers

We introduce a novel type of cw green laser source, the Protera 532, based on the intracavity frequency doubling of an extended-cavity, surface-emitting diode laser. The distinguishing characteristics of this platform are high compactness and efficiency in a stable, single-longitudinal mode with beam quality M2 < 1.2. The laser design is based on the previously reported NECSEL architecture used for 488nm lasers, and includes several novel features to accommodate different types of nonlinear optical materials. The infrared laser die wavelength is increased from 976nm to 1064nm without compromising performance or reliability. The intracavity frequency doubling to 532nm has been demonstrated with both bulk and periodically poled nonlinear materials, with single-ended cw power outputs of greater than 30 mW.

104 MHz rate single-shot recording with subpicosecond resolution using temporal imaging.

We demonstrate temporal imaging for the measurement and characterization of optical arbitrary waveforms and events. The system measures single-shot 200 ps frames at a rate of 104 MHz, where each frame is time magnified by a factor of -42.4x. Impulse response tests show that the system enables 783 fs resolution when placed at the front end of a 20 GHz oscilloscope. Modulated pulse trains characterize the systems impulse response, jitter, and frame-to-frame variation.

640 GHz real-time recording using temporal imaging

640 GHz chirped beat waves are recorded on a real-time scope and 2.2 ps pulses are recorded on a single-shot streak camera with 1000:1 dynamic range after -30times time magnification.

490-nm coherent emission by intracavity frequency doubling of extended cavity surface-emitting diode lasers

We describe a novel blue-green laser platform, based on the intracavity frequency doubling of Novalux Extended Cavity Surface Emitting Lasers. We have demonstrated 5 to 40mW of single-ended, 488nm, single-longitudinal mode emission with beam quality M2<1.2. The optical quality of these lasers matches that of gas lasers; their compactness and efficiency exceed ion, DPSS, and OPSL platforms. These unique properties are designed to serve diverse instrumentation markets such as bio-medical, semiconductor inspection, reprographics, imaging, etc., and to enable new applications. We also present data on the reliability of this novel laser platform and its extensions to different wavelengths (in particular, 460nm and 532nm) and to next-generation, highly compact, monolithic intracavity-doubled lasers.

Guided-Wave Temporal Imaging Based Ultrafast Recorders

Guided-wave parametric temporal imaging is demonstrated with 1.8 ps resolution and 1000:1 dynamic range. Waveforms are - 30.1 x time magnified before recording single-shot on a streak camera, and on a real-time oscilloscope repeating at MHz rates.

Performance results of the high-gain Nd:glass engineering prototype preamplifier module (PAM) for the National Ignition Facility (NIF)

We describe recent, energetics performance results on the engineering preamplifier module (PAM) prototype located in the front end of the 1.8 MJ National Ignition Facility laser system. Three vertically mounted subsystem located in the PAM provide laser gain as well as spatial beam shaping. The first subsystem in the PAM prototype is a diode pumped, Nd:glass, linear, TEM00, 4.5 m long regenerative amplifier cavity. With a single diode pumped head, we amplify a 1 nJ, mode matched, temporally shaped (approximately equals 20 ns) seed pulse by a factor of approximately 107 to 20 mJ. The second subsystem in the PAM is the beam shaping module, which magnifies the gaussian output beam of the regenerative amplifier to provide a 30 mm X 30 mm square beam that is spatially shaped in two dimensions to pre- compensate for radial gain profiles in the main amplifiers. The final subsystem in the PAM is the 4-pass amplifier which relay images the 1 mJ output of the beam shaper through four gain passes in a (phi) 5 cm X 48 cm flashlamp pumped rod amplifier, amplifying the energy to 17 J. The system gain of the PAM is 1010. Each PAM provides 3 J of injected energy to four separate main amplifier chains which in turn delivers 1.8 MJ in 192 frequency converted laser beams to the target for a broad range of laser fusion experiments.

Multiplexed gas spectroscopy using tunable VCSELs

Detection and identification of gas species using tunable laser diode laser absorption spectroscopy has been performed using vertical cavity surface emitting lasers (VCSEL). Two detection methods are compared: direct absorbance and wavelength modulation spectroscopy (WMS). In the first, the output of a DC-based laser is directly monitored to detect for any quench at the targeted specie wavelength. In the latter, the emission wavelength of the laser is modulated by applying a sinusoidal component on the drive current of frequency ω, and measuring the harmonics component (2ω) of the photo-detected current. This method shows a better sensitivity measured as signal to noise ratio, and is less susceptible to interference effects such as scattering or fouling. Gas detection was initially performed at room temperature and atmospheric conditions using VCSELs of emission wavelength 763 nm for oxygen and 1392 nm for water, scanning over a range of approximately 10 nm, sufficient to cover 5-10 gas specific absorption lines that enable identification and quantization of gas composition. The amplitude and frequency modulation parameters were optimized for each detected gas species, by performing two dimensional sweeps for both tuning current and either amplitude or frequency, respectively. We found that the highest detected signal is observed for a wavelength modulation amplitude equal to the width of the gas absorbance lines, in good agreement with theoretical calculations, and for modulation frequencies below the time response of the lasers (<50KHz). In conclusion, we will discuss limit of detection studies and further implementation and packaging of VCSELs in diode arrays for continuous and simultaneous monitoring of multiple species in gaseous mixtures.

Implementation of smoothing by spectral dispersion on Beamlet and NIF

The performance of the Beamlet laser with one dimensional smoothing by spectral dispersion implemented is investigated. Measurements of then ear field beam quality, nonlinear breakup, and transmission through spatial filter pinholes show a modest effect only at large SSD divergence. No measurable effect was found at the divergence level planned for indirect drive ignition experiments. The efficiency of conversion to the third harmonic was also measured with SSD present and found to be somewhat larger than expected form an ideal plane wave model.

Suppression of parasitics and pencil beams in the high-gain National Ignition Facility multipass preamplifier

The multi-pass amplifier (MPA) is the last subsystem of the NIF preamplifier, which feeds the main amplification stages of the NIF beamline. The MPA is based on a flashlamp pumped 5-cm diameter by 48 cm long Nd:glass rod amplifier operated at a single pass small signal gain of 15 to 17. The MPA is an off-axis multi-pass image relayed system, which uses two gain isolating image relaying telescopes and passive polarization switching using a Faraday rotator to output the pulse. We describe the MPA system, techniques used to avoid parasitic oscillation at high gain, and suppression of pencil beams. The system is used to generate a well- conditioned 22-joule output from one millijoule input. The output pulse requirements include 22 joules in a square, flat topped beam, and with near field spatial contrast of <5% RMS, square pulse temporal distortion <2.3, and an RMS energy stability of <3%. All of these requirements have been exceeded. The largest impediment to successful operation was overcoming parasitic oscillation. Sources of oscillation could be generally divided into two categories: those due to birefringence, which compromised the polarization contrast of the system; and those due to unwanted reflections from optical surfaces. Baffling in the vacuum spatial filters helps to control the system sensitivity to unwanted stray reflections from flat AR coated surfaces. Stress birefringence in the rather large glass volume of the rod (942 cm3) and the four vacuum loaded lenses are significant, as each of these elements is double passed between each polarizing beam splitter pass. This lowers the polarization contrast of the system, which can prevent the system from operating at sufficient gain. Careful analysis and layout of the MPA architecture has allowed us to address the challenges posed by a system small signal gain of ≈ 33000 and with an output pulse of as high as 27 joules.