We present a new technique combining digital holography and tomography to make path-resolved measurements of a turbulent air volume. An array of optical beams at different propagation angles is transmitted through the volume under test, interfered with a reference beam, and the resulting fringe patterns are all simultaneously recorded on a focal plane array. The complex field of each beam in the receiver pupil plane is recovered via digital Fourier processing and then tomographic reconstruction algorithms are applied to calculate wavefront error contributions from multiple planes along the beam path. Results are presented from a proof-of-concept laboratory experiment using phase screens to mimic the turbulence volume. Comparing the tomographic reconstructions to the known screen prescriptions, we successfully demonstrate accurate measurement of the phase distortions introduced in multiple planes. This ability to longitudinally resolve turbulence and isolate individual layers may benefit numerous applications including precision turbulent flow analysis in wind tunnels and adaptive optic compensation for free space optical communications.
We report on digital holographic imaging through atmospheric turbulence. Data recorded with aberrations is corrected during post processing using an iterative sharpness-metric maximization algorithm. Assuming the correction cancels the actual wavefront error, this process is equivalent to wavefront sensing. Much of our past work focused on imaging through isotropic turbulence with phase corrections using a Zernike-polynomial expansion. Here, we describe algorithm modifications for imaging through anisotropic turbulence, similar to what is seen when looking through the aero-optic boundary layer surrounding a moving aircraft. Specifically, we explore tradeoffs associated with switching from a Zernike representation to Karhunen-Loève basis functions. In some cases, the dimensionality of the phase correction estimation algorithm can be reduced significantly by this change. This reduces the computational burden
We report on the performance of seeded Raman fiber amplifiers based on multimode gradient index fiber. The "beam
cleanup" improvement in beam quality of the Stokes beam over that of input pump beam (previously observed in
unseeded fiber amplifier geometries using stimulated Raman scattering in multimode graded index fiber) is shown here
to be limited by the beam quality of the input seed beam for seeded amplifier configurations. The amplifiers are
characterized in terms of their capacity for beam-cleanup, their ability to amplify the seed and in terms of their output
spectra. The advantages and disadvantages of a backward-pumped geometry versus a forward-pumped geometry are
discussed. Depending on the geometry, amplified power can be readily distributed to a cascade of Stokes frequencies
(unseeded forward-pumped geometry) or can be mostly contained in the seed frequency (seeded backward-pumped
geometry).
Phasing of two-channel cw master oscillator/power amplifier beams using an SBS phase conjugate mirror has been demonstrated. The phasing was achieved for a two-channel master oscillator/power amplifier system, which used a single-frequency Nd:YAG master oscillator, two parallel fiber amplifiers, and a fiber phase conjugate mirror in a double-pass configuration. The successful phasing of two cw amplifier beams with a fiber phase conjugate mirror greatly enhances the prospects for phasing of multiple laser amplifiers without complex servo-loop control systems.
The space charge region associated with the second-order nonlinearity in thermally poled fused silica was examined using secondary ion mass spectrometry (SIMS). Results for four samples are presented here: two flame-fused quartz samples (type-II fused silica), a higher purity flame-fused synthetic (type-III) fused silica, and a type-II fused silica treated with deuterated water. SIMS results show: (1) ionic depletion regions formed by migration of alkali ion impurities with different mobilities, (2) injection of surface alkali contaminants arising from the high surface fields, and (3) evidence of field injection as well as thermal diffusion of adsorbed surface water.
When an electric field is applied to a heated piece of bulk silica glass, which is subsequently cooled with the field applied, a permanent second order nonlinearity is formed.Here we examine the formation of the nonlinearity in situ via real-time observation of the second harmonic signal. The dynamics of the growth and decay of the signal are dependent on filed polarity, sample history and ambient environment during heating. The in situ dynamics indicate that under field reversal, there can be a long delay in creating or destroying the nonlinearity.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.