The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory contains a 192-beam 4.2 MJ neodymium glass laser (around 1053 nm or 1w) that is frequency converted to 351nm light or 3w. It was built to access the extreme high energy density conditions needed to support the nation’s nuclear stockpile in the absence of further underground nuclear tests, including studying Inertial Confinement Fusion (ICF) and ignition in the laboratory.
Over the last year, important results have been obtained demonstrated a fusion yield of 1.35MJ with 1.9MJ of laser energy (and 440 TW power) injected in the target, bringing the NIF to the threshold of ignition [2-3]. As the yield curve near ignition is steep, the laser performance team has focused on providing improved power accuracy and precision (better shot-to-shot reproducibility) with a high-fidelity pulse shaping system (HiFiPS), and also on extending the NIF operating power and energy space by 15% to 2.2MJ and 500TW.
The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory contains a
192-beam 4.2 MJ neodymium glass laser (around 1053 nm or 1w) that is frequency converted to
351nm light or 3w. It has been designed to support the study of Inertial Confinement Fusion (ICF)
and High Energy Density Physics (HEDP). The NIF Precision Diagnostic System (PDS) was reactivated and new
diagnostic packages were designed and fielded that offer a more comprehensive suite
of high-resolution measurements. The current NIF laser performance will be presented as well as the preliminary results obtained with the various laser experimental campaigns using the new diagnostic tool suites.
We used a Monte Carlo method to generate error bars for deconvolved measurements from diagnostics on the National Ignition Facility (NIF). Through a process of masking and normalization of the diagnostic system’s known Impulse Response Function (IRF), we were able to diminish the deconvolved measurement error for all points of the waveform by a factor of < 2. This technique is generally applicable to deconvolutions with measured IRFs.
Pixel-array array detectors allow single-photon counting to be performed on a massively parallel scale, with several million counting circuits and detectors in the array. Because the number of photoelectrons produced at the detector surface depends on the photon energy, these detectors offer the possibility of spectral imaging. In this work, a statistical model of the instrument response is used to calibrate the detector on a per-pixel basis. In turn, the calibrated sensor was used to perform separation of dual-energy diffraction measurements into two monochromatic images. Targeting applications include multi-wavelength diffraction to aid in protein structure determination and X-ray diffraction imaging.
Fast beam-scanning non-linear optical microscopy, coupled with fast (8 MHz) polarization modulation and analytical modeling have enabled simultaneous nonlinear optical Stokes ellipsometry (NOSE) and linear Stokes ellipsometry imaging at video rate (15 Hz). NOSE enables recovery of the complex-valued Jones tensor that describes the polarization-dependent observables, in contrast to polarimetry, in which the polarization stated of the exciting beam is recorded. Each data acquisition consists of 30 images (10 for each detector, with three detectors operating in parallel), each of which corresponds to polarization-dependent results. Processing of this image set by linear fitting contracts down each set of 10 images to a set of 5 parameters for each detector in second harmonic generation (SHG) and three parameters for the transmittance of the fundamental laser beam. Using these parameters, it is possible to recover the Jones tensor elements of the sample at video rate. Video rate imaging is enabled by performing synchronous digitization (SD), in which a PCIe digital oscilloscope card is synchronized to the laser (the laser is the master clock.) Fast polarization modulation was achieved by modulating an electro-optic modulator synchronously with the laser and digitizer, with a simple sine-wave at 1/10th the period of the laser, producing a repeating pattern of 10 polarization states. This approach was validated using Z-cut quartz, and NOSE microscopy was performed for micro-crystals of naproxen.
A beam-scanning microscope based on Lissajous trajectory imaging is described for achieving streaming 2D imaging with continuous frame rates up to 1.4 kHz. The microscope utilizes two fast-scan resonant mirrors to direct the optical beam on a circuitous trajectory through the field of view. By separating the full Lissajous trajectory time-domain data into sub-trajectories (partial, undersampled trajectories) effective frame-rates much higher than the repeat time of the Lissajous trajectory are achieved with many unsampled pixels present. A model-based image reconstruction (MBIR) 3D in-painting algorithm is then used to interpolate the missing data for the unsampled pixels to recover full images. The MBIR algorithm uses a maximum a posteriori estimation with a generalized Gaussian Markov random field prior model for image interpolation. Because images are acquired using photomultiplier tubes or photodiodes, parallelization for multi-channel imaging is straightforward. Preliminary results show that when combined with the MBIR in-painting algorithm, this technique has the ability to generate kHz frame rate images across 6 total dimensions of space, time, and polarization for SHG, TPEF, and confocal reflective birefringence data on a multimodal imaging platform for biomedical imaging. The use of a multichannel data acquisition card allows for multimodal imaging with perfect image overlay. Image blur due to sample motion was also reduced by using higher frame rates.
Photon counting represents the Poisson limit in signal to noise, but can often be complicated in imaging
applications by detector paralysis, arising from the finite rise / fall time of the detector upon photon absorption.
We present here an approach for reducing dead-time by generating a deconvolution digital filter based on
optimizing the Fisher linear discriminant. In brief, two classes are defined, one in which a photon event is
initiated at the origin of the digital filter, and one in the photon event is non-coincident with the filter origin.
Linear discriminant analysis (LDA) is then performed to optimize the digital filter that best resolves the
coincident and non-coincident training set data.1 Once trained, implementation of the filter can be performed
quickly, significantly reducing dead-time issues and measurement bias in photon counting applications.
Experimental demonstration of the LDA-filter approach was performed in fluorescence microscopy
measurements using a highly convolved impulse response with considerable ringing. Analysis of the counts
supports the capabilities of the filter in recovering deconvolved impulse responses under the conditions
considered in the study. Potential additional applications and possible limitations are also considered.
Despite the ubiquitous use of multi-photon and confocal microscopy measurements in biology, the core techniques
typically suffer from fundamental compromises between signal to noise (S/N) and linear dynamic range (LDR). In this
study, direct synchronous digitization of voltage transients coupled with statistical analysis is shown to allow S/N
approaching the theoretical maximum throughout an LDR spanning more than 8 decades, limited only by the dark counts
of the detector on the low end and by the intrinsic nonlinearities of the photomultiplier tube (PMT) detector on the high
end. Synchronous digitization of each voltage transient represents a fundamental departure from established methods in
confocal/multi-photon imaging, which are currently based on either photon counting or signal averaging. High
information-density data acquisition (up to 3.2 GB/s of raw data) enables the smooth transition between the two
modalities on a pixel-by-pixel basis and the ultimate writing of much smaller files (few kB/s). Modeling of the PMT
response allows extraction of key sensor parameters from the histogram of voltage peak-heights. Applications in second
harmonic generation (SHG) microscopy are described demonstrating S/N approaching the shot-noise limit of the detector
over large dynamic ranges.
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