RESUMO
An entirely reflective slit spatial filter is proposed to provide spatial filtering, gain isolation, and ASE mitigation for high-energy laser systems. The traditional circular pinhole is replaced by two orthogonal slits, which lowers the intensity at the spatial filter plane by up to two orders of magnitude, and by using reflective optics we reduce spatial dispersion and eliminate B-integral effects. A ray trace model of the spatial filter shows excellent transmitted wavefront, but also indicates aberrations at the foci from using cylindrical optics at 45°. It is expected that the use of off-axis parabolic mirrors would mitigate this issue but comes at the cost of more complicated, expensive optics and more complex alignment. We created a numerical model based on Fourier optics to explain this effect and guide design requirements to mitigate it. High-quality imaging and filtering capabilities are demonstrated experimentally.
RESUMO
We report on two-photon absorption measurements at 213 nm of deep UV transmissible media, including LiF, MgF2, CaF2, BaF2, sapphire (Al2O3), and high-purity grades of fused-silica (SiO2). A high-stability 24 ps Nd:YAG laser operating at the 5th harmonic (213 nm) was used to generate a high-intensity, long-Rayleigh-length Gaussian focus inside the samples. The measurements of the fluoride crystals and sapphire indicate two-photon absorption coefficients between 0.004 and 0.82 cm/GW. We find that different grades of fused silica performed near identically for two-photon absorption; however, there are differences in linear losses associated with purity. A low two-photon absorption cross section is measured for MgF2, making it an ideal material for the propagation of high-intensity deep UV lasers.
RESUMO
Amplification of broadband frequency-modulated (FM) pulses in high-efficiency materials such as ytterbium-doped strontium fluorapatite results in significant gain narrowing, leading to reduced on-target bandwidths for beam smoothing and to conversion from frequency modulation to amplitude modulation (AM). To compensate for these effects, we have applied precision spectral sculpting, requiring both amplitude and phase shaping, to the amplification of broadband FM pulses in narrow-band gain media. We have demonstrated sculpting for centerline small-signal gains of 10(4), producing amplified pulses that have both sufficient bandwidths for on-target beam smoothing and temporal profiles that have no potentially damaging AM.
RESUMO
Ytterbium-doped Sr(5)(PO(4))(3)F was successfully lased at 985 nm in quasi-cw mode with a slope efficiency of 74% and an absorbed threshold energy of 18 mJ. Q-switched slope efficiencies of 21% were obtained with a maximum energy of 9.4 mJ in 8.8-ns pulses.
RESUMO
We report on the experimental measurement of the saturated gain of Yb(3+):Sr(5)(PO(4))(3)F at the 1047-nm laser line as a function of pump fluence and probe energy. The emission line was accurately modeled as a single homogeneous extraction, yielding values of 6.2 x 10(-20) cm(2) for the emission cross section and 3.3 J/cm(2) for the saturation fluence.
RESUMO
The stimulated Raman-scattering (SRS) gain coefficient has been measured quantitatively for the first time to our knowledge in Yb:Sr(5)(PO(4))(3)F to be 1.23 ? 0.12 cm/GW at 1053 nm. These data, along with surface and bulk losses, feedback that is due to surface reflections, gain saturation, and bandwidth, have been applied to a quantitative model that predicts the effects of SRS within a laser amplifier system where the laser gain media show SRS gain. Limitations and impact to the laser amplifier performance are discussed, along with possible techniques to reduce SRS loss.