The concept of high energy density (HED) radiation driven momentum coupling (momentum
transfer), CM, to a targets in a vacuum is analytically developed and applied via successive plasma,
ablative, and hydrodynamic interfaces undergoing both weak and strong shocks. CM are derived from
equations of state (EOS) variables and serve as figures of merit to determine energy efficiency conversion
into target momentum. Generally, CM are proportional to the inverse of the interaction speed and related
variables for each interaction regime. This approach provides a formalism allowing computation of hitherto
intractable HED radiation and mechanical momentum coupling interactions encountered in astrophysics,
planetary physics, inertial confinement fusion, near-Earth object hazard mitigation, and HED explosives
modeling. CM is generally not scale invariant as are the hydrodynamic Euler equations. This analytic
procedure supports interpretation of experiments using EOS response of material targets to HED
interactions on the meso - and macro-scales to describe CM.
Sandia National Laboratories NLS (1064 nm) and Z-Beamlet (527 nm) pulsed lasers @ ~ 100 GW/cm2 and 10
TW/cm2 were used to attain pressures at 20 - 525 GPa on a variety of metallic and mineral targets. A simple,
inexpensive and innovative electro-optical real-time methodology monitored rear surface mechanical deformation and
associated particle and shock wave velocities that differ considerably between metals and non-metals. A reference
calibration metal (Aluminum) and a reference non-metal (graphite) were used to demonstrate the validity of this
methodology. Normative equations of state and momentum coupling coefficients were obtained for dunite,
carbonaceous meteorites, graphite, iron and nickel. These experimental results on inhomogeneous materials can be
applied to a variety of high energy density interactions involving stellar and planetary material formation, dynamic
interactions, geophysical models, space propulsion systems, orbital debris, materials processing, near-earth space (lunar
and asteroid) resource recovery, and near-earth object mitigation models.
This paper discusses the momentum coupling coefficient in the relativistic, collisionless realm as contrasted with the collisional, ablation dominated regime. It is shown the total momentum coupling coefficient is a result of the combined ion and photon momenta.
Energy requirements for near-Earth object (NEO) threat mitigation are addressed. Due to a large NEO mass range and the possibility of limited available time for orbit change, energy requirements can be large (~petajoules). To quantitatively determine energy requirements for a given momentum change use is made of the momentum coupling coefficient, CM, that depends on the type of energy transfer, energy density, interaction time scale, and target material properties. Inhomogeneous and flawed NEO materials are empirically confronted through experimental methodologies that generate parameters on high energy density mechanical and radiative induced momentum coupling to (primarily) meteorite targets serving as near-Earth asteroid surrogates. Interactants include high speed (> 8 km/s) mechanical projectiles, high intensity (~ GW/cm2) infra-red laser radiation, and (~200 GW/cm2) soft X-ray radiation. Issues exists and are addressed regarding momentum coupling scaling from coupon sized (~mm2) to much larger (~m2) targets. Applications include high energy planetary and astrophysical momentum coupling dynamics.
Experiments on pure and inhomogeneous materials (meteorite samples) have been performed at the Sandiad National Laboratory (SNL) using a hohlraum source of soft X-rays. It is of interest to deduce the scaling of the ablation pressure with the radiation temperature in this class of experiment. This paper uses similarity relations deduced from a radiation diffusion model together with several theoretical expressions for the Rosseland mean free path of the target material. The resulting scaling laws are compared. The momentum coupling coefficient scaling with input radiation temperature is also given. As an example of the methodology, scaling results are given for the types of meteorites used in these recent experiments as well as for a comet model based on opacities obtained from the LANL TOPS code. This work is part of an on-going program to model the dymanic properties and interactions of Near Earth Object (NEO) materials in the context of NEO hazard mitigation.
When a single-pulse high-power laser irradiates a surface at atmospheric pressure, a laser supported detonation (LSD) wave can form above the target surface. The high-pressure gas behind the LSD wave transfers momentum to the target. The laser target coupling is substantially reduced in vacuum, the coupling coefficient typically being an order of magnitude less than that when an atmosphere is present. Another pressure enhancement technique is to confine the laser-target interface. Confinement or 'tamping' also can substantially increase the momentum coupling to the target. Experiments tend to differ from one another based on the target size (thickness) and confinement geometry. This work describes and compares some experimental results for metallic targets irradiated by 1054 nm radiation in the GW/cm2 range and interprets them in terms of simple models. As will be discussed in this paper, such models predict a weak sensitivity to target materials but results are likely to be different for inhomogeneous materials as has been seen in recent experiments on iron-nickel and stony meteorites.
We have developed an innovative method using radiation produced by in flight annihilation of energetic positrons to detect hidden explosives and other illegal substances. The system uses either radioisotope or compact accelerator based methods to generate a high energy positron beam. The high energy positrons annihilate in flight producing a tunable, narrow spectrum beam of high energy photons. The photon energy, which is determined by the positron energy, can be chosen to be resonant with elements of the explosive or other target. The concentration of the target material determines the intensity of the return signal. Standard gamma radiation detection techniques are used to detect the emitted gamma rays. Because of the innovative method we use to generate and monochromatize the positron beam, the entire system is inexpensive, compact and portable.
This paper analyzes laser induced impulse and associated scaling laws appropriate to the intensity range of interest for laser space debris clearing (106 - 1010 W/cm2). A simple radiative fluence model is used augmented by empirical values from some recent experiments.
Semiconductor laser diode (LD) coherent light source coupling is critical to integrated optic (IO) performance. Direct external coupling of conventional (CD layer) LDs is often inefficient, introduces noise, and is generally counter to the IO micro-concept. Two options are suggested; fiber optic coupling to the IO chip aperture and integration (hybridization) of micro-LDs within the IO chip itself. Selection of the optimal LD for integration into IOs depends on a variety of parameters specific to the IO application. As an example, laboratory displacement measurements were carried out with a conventional (780 nm) edge emitting LD externally attached to an IO Michelson interferometer (IOMI) chip at the waveguide aperture. Measurement error analysis identifies errors and suggests how digital, thermal, electronic, and optical source errors can be minimized through electronic design and micro-LD components. Characteristics of LDs, VCELS and ring-laser didoes, such as threshold current, operating voltage, thermal effects, mode structure, loss mechanisms, and related coupling characteristics are compared. Recommendations for improving analog/digital conversion and software methods, as well as applications of vertical cavity surface-emitting lasers and semiconductor ring lasers coupled to IO chips are discussed.
Adaptive and active optics in general, and laser power beaming in particular, requires the construction of large, complex mirror systems. Since these mirrors need to be tested with high accuracy to achieve optimum performance, their unusual shape and size often require the construction of special testing equipment. A full-surface interferometric scanning (FSIS) system for testing large cylindrical surfaces, which cannot be readily tested with current commercial interferometer systems, is described. The FSIS approach, using grating shearing interferometry, is based on interferometric slope measurement along the long direction of the cylindrical surface under test. The full surface measurement is synthesized from a discrete set of subaperture measurements obtained by scanning in the direction of the long side of the cylindrical surface. The FSIS is characterized by a high degree of immunity from the effects of vibration.
Adaptive optics (AO) segmented array systems require los cost nm (piston) and (mu) rad (tilt) range displacement edge sensors to assist in establishing phase continuity between adjacent segments by measuring relative AO edge displacements. Preliminary laboratory experiments using Si based integrated optic (IO) chips coupled to laser diode sources were carried out to determine their suitability as low cost, miniature, reliable and high precision piston and tilt edge sensors. Edge sensor displacement experiments demonstrate a resolution (sensitivity) on the order of 10 nm. The IO chip used is a micro-version (7.5 X 7.5 X 0.5 mm3) of a double beam Michelson interferometer with a phase shifter to allow direction determination. Operating at a wavelength 770 < (lambda) < 790 nm and a power output < 50 (mu) W, the wavelength stability, within a temperature range 15 to 35 degree(s)C, is (Delta) (lambda) 0/(lambda) 0 equals 10-6. A 1 kHz frequency response was achieved for displacements on the order of 100 micrometers (measuring range) and 106 Hz at 100 nm displacement, with a logarithmic frequency response increasing with decreasing measuring range. The maximum linear (moving) relative speed between adjacent segments is 200 mm/s or 200 X 106 nm/s, allowing MHz sampling rates. Synchronously calibrated experiments of IO performance against a capacitance gauge, closed loop calibrated piezo stepper, and a HeNe source interferometer are presented. Systems integration design of the IO chip as a sensor is described.
The need for a number of interferometric sensor systems during fabrication, assembly and operation of large segmented array mirrors, is discussed. Specifically, an interferometric approach is described for calibrating edge sensors and actuators, and aligning the segments during mirror assembly.
An analytical study of laser diode (LD) operation coupled to external cavity scattering elements, which function as variably coupling reflectors (VCRs), is carried out with the purpose of determining the interrelationship between cavity coupling and intracavity optical intensity which determine the current generated at the rear facet PIN detector. If the external cavity coupling is position sensitive it can allow the relative position between the LD and the external cavity to be determined from the PIN or other detector mounted with the LD. If the LD and external cavity element are placed on opposite edges of two adjacent adaptive optics segments they can provide the basis for a self aligning position sensor; the amount of current detected at the PIN or other detector will depend on the relative displacement between the LD and external coupling element. Schematics of the edge sensors, the basic electronic configuration, and the optics of the external cavity are given. The ratio of the internal cavity intensity, Ic, to the saturation intensity, Is, is plotted as a function of the external cavity coupling. When this ratio approaches one, large-signal output is not a linear function of large-signal output. For operation well below saturation, the PIN detector current is directly related to Ic and may serve as a reliable detector.
Several new applications of excimer lasers in industry and medicine have increased the requirements for control of excimer laser beam parameters. Some applications require precise control of spatial uniformity, pulse-to-pulse amplitude variations and temporal profiles. The spatial and temporal characteristics of excimer laser beams are affected by small changes in laser gas composition. The role of gas composition, as well as methods for controlling gas composition, are discussed in relation to critical beam parameters.
Excimer laser performance and operational efficiency can be enhanced by simultaneously applying several different approaches related to gas technology. Causes of laser beam power and profile decay, as well as degradation of laser cczriponents are detailed with special regard to laser gases. 4ethods for canbating these deleterious effects are then detailed. These include in—depth discussion of (1) initial gas purity, (2) gas handling between source and laser, (3) laser operating techniques, and (4) in—situ gas purification.
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