Bulk scattering in polycrystalline laser materials (PLM), due to non-uniform refractive index across the bulk, is regarded as the primary loss mechanism leading to degradation of laser performance with higher threshold and lower output power. The need for characterization techniques towards identifying bulk scatter and assessing the quality. Assessment of optical quality and the identification of bulk scatter have been by simple visual inspection of thin samples of PLMs, thus making the measurements highly subjective and inaccurate.
A modified white light Schlieren Imaging Setup utilizing variable focusing capability is demonstrated. The white light Schlieren Imaging Setup makes it possible to image the spatial variations in the refractive index in the PLMs regardless of dimensions, which are the cause of bulk scattering loss in a transparent material over the entire cross-sectional area of the sample. The high sensitivity of white light Schlieren provides the ability of directly imaging the local spatial variations in refractive index across the entire sample dimension and compare different samples.
Bulk scattering in polycrystalline laser materials (PLM), due to non-uniform refractive index across the bulk, is regarded as the primary loss mechanism leading to degradation of laser performance with higher threshold and lower output power. The need for characterization techniques towards identifying bulk scatter and assessing the quality. Assessment of optical quality and the identification of bulk scatter have been by simple visual inspection of thin samples of PLMs, thus making the measurements highly subjective and inaccurate. Angle Resolved Scatter (ARS) measurement allows for the spatial mapping of scattered light at all possible angles about a sample, mapping the intensity for both forward scatter and back-scatter regions. The cumulative scattered light intensity, in the forward scatter direction, away from the specular beam is used for the comparison of bulk scattering between samples. This technique employ the detection of scattered light at all angles away from the specular beam directions and represented as a 2-D polar map. The high sensitivity of the ARS technique allows us to compare bulk scattering in different PLM samples which otherwise had similar transmitted beam wavefront distortions.
Bulk scattering in polycrystalline laser materials (PLM), due to non-uniform refractive index distribution across the bulk, is regarded as the primary loss mechanism leading to degradation of laser performance with higher threshold and lower output power. There is a need for characterization techniques, towards identifying bulk scatter and assessing the quality. Assessment of optical quality and the identification of bulk scatter have been by simple visual inspection of thin samples of PLMs, thus making the measurements highly subjective and inaccurate. Transmitted Beam Wavefront Profiling (TBWP) allows for the direct and quick imaging of the distortions introduced by bulk scattering, which is a direct manifestation of the presence of refractive index inhomogeneities in the PLM sample. As a laser beam propagates through the PLM sample, different regions of the incident beam experience different refractive index profiles, which cause spatial distortions to the beam. TBWP is able to directly and quickly image these distortions introduced to a propagating laser beam caused by the presence of bulk scattering in the PLMs.
0.5% Holmium (Ho) doped YAG single crystal fiber (SCF) was fabricated using the laser heated pedestal growth
(LHPG) method and amplification properties of the fabricated Ho:YAG SCF were studied. The relatively large lengthto-
diameter ratio provides guiding for both the pump and signal beams propagating in the SCF. The propagation and
gain of signals with different modes were studied. A numerical method based on finite difference (FD) beam
propagation method (BPM) combined with the rate equations was developed for theoretical simulation. The results are
encouraging to demonstrate the advantages of SCF for its fiber-like beam guiding property and solid state material gain
property. The simulation tool provides details about how the fiber shape and launched mode affect the gain and output
beam shape as well as predicts the amplification behavior of such unique specialty fibers.
The current effort reports on the spectroscopic properties (absorption, emission and fluorescence lifetime) as a function
of varying Erbium concentration in Y2O3. Results show a non-linear behavior in the fluorescence lifetimes and the
radiative-emission intensities for the 4I11/2 and the 4I13/2 energy levels.
Many advances have been made recently in both solid-state and semiconductor based mid-wave
infrared (MWIR) and long-wave infrared (LWIR) laser technologies, and there is an ever growing
demand for these laser sources for Naval, DOD and homeland security applications. We will
present various current and future programs and efforts at Naval Air Warfare Center Weapons
Division (NAWCWD) on the development of high-power, broadly tunable MWIR/LWIR lasers for
sensing applications.
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