Radiative feedback (RFB) from stars plays a key role in galaxies, but remains poorly-understood. We explore this using high-resolution, multi-frequency radiation-hydrodynamics (RHD) simulations from the Feedback In Realistic Environments (FIRE) project. We study ultra-faint dwarf through Milky Way mass scales, and explore a variety of RHD effects including H and He photo-ionization; photo-electric, Lyman Werner, Compton, and thermal dust heating; singlescattering (UV) and IR multiple-scattering radiation pressure (RP). We also compare fundamentally distinct numerical RHD algorithms: the ray-based LEBRON method (exact in optically-thin limits) and moments-based M1 method (exact in optically-thick limits). In all cases, the most important RFB channels on galaxy scales are photo-ionization heating and single-scattering RP: at all galaxy masses, most of the ionizing/far-UV luminosity from young stars (∼ 1/2 of the lifetime-integrated bolometric) is absorbed. In dwarfs, the most important effect is photo-ionization heating from the meta-galactic background suppressing accretion onto the galaxy. In MW-mass galaxies the meta-galactic background has negligible effects; but local photo-ionization and single-scattering RP both contribute significantly to regulating the galactic star formation efficiency and lowering central densities. Without some RFB (or some other "rapid" FB), resolved GMCs turn most of their mass into stars, making galaxies dominated by hyper-dense, bound star clusters. This also makes star formation more violent and "bursty" when SNe eventually explode in these hyper-clustered objects: thus, including RFB tends to "smooth" SFHs. These conclusions are robust to the numerical RHD method, but the M1 method produces somewhat stronger RFB effects. As in previous FIRE simulations, we show IR multiple-scattering is rare (contributing negligibly in low-metallicity dwarfs, and just ∼ 10% of the RP in massive galaxies): the majority of photon absorption occurs in "normal" GMCs with order-unity A V .

A non-destructive and highly selective method of standoff detection is presented and quantitatively evaluated. The method is found to be orders of magnitude more sensitive than previous coherent spectroscopy methods, identifying concentrations as low as 2 lg/cm 2 of an explosive simulant mixed in a polymer matrix. The approach uses a single amplified femtosecond laser to generate high-resolution multiplex coherent anti-Stokes Raman scattering (CARS) spectra encompassing the fingerprint region (400À2500 cm À1) at standoff distance. Additionally, a standoff imaging modality is introduced, visually demonstrating similar sensitivity and high selectivity, providing promising results toward highly selective trace detection of explosives or warfare agents.

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