A metamaterials-based approach to making a wide-angle absorber of infrared radiation is described. The technique is based on an anisotropic Perfectly Impedance Matched Negative Index Material (PIMNIM). It is shown analytically that a sub-wavelength in all three dimensions PIMNIM enables absorption of close to 100% for incidence angles up to 45 deg to the normal. A specific implementation of such frequency-tunable PIMNIM based on plasmonic metamaterials is presented. Applications to infrared imaging and coherent thermal sources are described.PACS numbers:

The intensity of a subpicosecond laser pulse was amplified by a factor of up to 1000 using the Raman backscatter interaction in a 2 mm long gas jet plasma. The process of Raman amplification reached the nonlinear regime, with the intensity of the amplified pulse exceeding that of the pump pulse by more than an order of magnitude. Features unique to the nonlinear regime such as gain saturation, bandwidth broadening, and pulse shortening were observed. Simulation and theory are in qualitative agreement with the measurements. The invention of chirped pulse amplification (CPA) [1,2] led to a tremendous increase of ultrashort laser pulse intensities to above 10 20 W=cm 2 [3,4]. However, such an ultrahigh intensity laser system was achieved using very large (on the order of 1 m 2 ) and expensive compressor gratings [4]. A further increase of the pulse intensity using the CPA technique would require even larger gratings in order not to exceed the material damage threshold. Such a system would be very difficult to implement in universityscale laboratories.In order to overcome the CPA material limit at ultrahigh intensities, different backscattering coupling techniques were proposed in plasma, including Compton scattering [5], resonant Raman backscattering [6], and Raman backscattering at an ionization front [7]. The experiments reported here utilize the resonant Raman mechanism [6], where a short seed laser pulse is amplified by a counterpropagating long pump pulse, with their frequencies satisfying the resonance relation, ! pump ! seed ! pe where ! pump , ! seed , and ! pe are frequencies of pump, seed, and plasma, respectively; ! pe 4 e 2 n e =m e p , n e is the plasma electron density, and m e and e are mass and charge of an electron. The energy transfer from pump to seed is in proportion to their frequencies, so for ! pump 10! pe , the efficiency can be as high as 90%. What makes the resonant Raman backscatter regime attractive is that it is a simple resonant interaction, with the seed amplification strong enough to outrun other deleterious competing instabilities (such as modulational instability that can lead to the filamentation of the laser beam) [6] or to avoid superluminous precursor solutions [8], and with realizable highly compressed ultrashort pulse solutions [9].The Raman backscattering (RBS) amplification can be divided into linear and nonlinear regimes. In the linear regime the pump depletion is negligible and the gain is independent of the seed intensity. The seed pulse is amplified and increased in duration due to the narrow bandwidth of the linear amplification. The nonlinear regime, the socalled -pulse regime, is characterized by pump depletion and the simultaneous temporal compression of the amplified pulse. In this regime, the Raman amplification and compression of ultrashort pulses in a plasma allow intensities to reach 10 20 -10 21 W=cm 2 in a compact universityscale device, and unprecedented high intensity on the order of 10 25 W=cm 2 in a larger system [9]. Such intensities open new frontiers i...

Conventional adaptive-optics systems correct the wavefront by adjusting a deformable mirror (DM) based on measurements of the phase aberration taken in a pupil plane. The ability of this technique, known as phase conjugation, to correct aberrations is normally limited by the maximum spatial frequency of the DM. In this paper we show that conventional phase conjugation is not able to achieve the dark nulls needed for high-contrast imaging. Linear combinations of high frequencies in the aberration at the pupil plane "fold" and appear as low-frequency aberrations at the image plane. After describing the frequency-folding phenomenon, we present an alternative optimized solution for the shape of the deformable mirror based on the Fourier decomposition of the effective phase and amplitude aberrations.

We present numerical studies of recombination gain in the transition to the ground state of H-like C (2 → 1 transition at = 3.4 nm). It is shown that high gain (up to about 180 cm −1) can be achieved using currently available, relatively compact, laser technology. The model includes the ionization of the plasma by an ultraintense, ultrashort laser pulse, followed by plasma expansion, cooling, and recombination. Transient population inversion is generated during the recombination process. We investigate the behavior of the gain with respect to different plasma parameters and pump pulse parameters and explain how the different properties of the plasma and the pump pulse affect the gain.

The frequency upshifting of 0.8 μm picosecond laser pulses was demonstrated using the temporal change of the free carrier density in a ZnSe semiconductor crystal. The crystal was ionized by transverse propagating ps pulses. Shifts of up to 1.6 nm were observed, which agree within 25% with the theory.