Optimal solution for the multilayers AR coating of 4J solar cell including design and fabrication was investigated. The real layer structure of 4J solar cell was determined first through reverse fitting, then the multilayers AR coating could be designed on the complete 4J solar cell to find the global optimization. After clarifying that the performance of multilayers AR coating is affected by oxidation of AlInP, the oxide layer was characterized and compensated to improve the spectrum. Through transmission electron microscopy (TEM), the oxidation depth was determined to be 5nm. Finally, the multilayers AR coating was re-optimized by considering oxidation layer into 4J solar cell. Using ion assisted deposition, the multilayers AR coating was fabricated with a slightly increased weight average reflectance of only 0.5%.
A Tm:YLF laser in INNOSLAB design is reported. It produces 200 W of output power at an optical efficiency of 24 % and a slope efficiency of 27 % with respect to incident pump power. The laser crystal is partially end-pumped in a tophat line focus with a width of 12 mm and a height of about 1 mm. It is placed in a stable, spherical laser resonator, which results in a highly elliptical output beam. The beam is near diffraction limit and Gaussian in shape in one axis and contains very high order transversal modes and is Top-Hat-like in shape in the other axis. The beam shape is ideal for pumping a Ho:YLF laser crystal in INNOSLAB design for a pulsed amplifier.
We report on a single-frequency laser oscillator based on a new Er:YLuAG laser crystal which is spectrally suitable for
application as a transmitter in differential absorption lidar measurements of atmospheric CH<sub>4</sub>. The laser emits singlefrequency laser pulses with 2.3 mJ of energy and 90 ns duration at a repetition rate of 100 Hz. It is resonantly pumped by two linearly polarized single-mode cw fiber lasers at 1532 nm. A scan of the CH<sub>4-</sub>absorption line at 1645.1 nm was performed and the shape of the line with its substructure was reproduced as theoretically predicted. A 2.5-dimensional performance model was developed, in which pump absorption saturation and laser reabsorption is included. Also the spectral output of the laser oscillator longitudinal multimode operation could be predicted by the laser model.
A single-frequency master-oscillator fiber power-amplifier operating at 1991 nm was demonstrated. The seeding laser
was a diode-pumped, high efficient, single-longitudinal-mode Tm:YAP laser with a coupled-cavity configuration. 721
mW single-frequency output power was obtained at 1991 nm, the slope efficiency was 46%. The power amplifier was a
diode-pumped Tm-doped fiber. 8.6 W single frequency output power was obtained from the amplifier. The maximum
output power was limited by the low coupling efficiency of the seeding signal into the fiber core. The strength of ASE in
the fiber amplifier with respect to the power of input signal was studied experimentally. High power single-frequency
lasers at 2 μm optical region have potential applications on eye-safe coherent lidar and optical remote sensing.
Development of 2 micron solid-state lasers has attracted a great deal of attention in recent years, because 2 micron lasers
have many potential applications in various fields, such as remote sensing, medical application, laser radar, and optical
communication in space. The MOPA system is an effective way to obtain high energy and good frequency and beam
qualities which are required in coherent lidars. The traditional MOPA systems use injection seeding technology to obtain
narrow linewidth and high power/energy laser output at the same time. Feedback control makes systems of injection
seeding MOPA more complicated in applications. Thanks to the fast development of fiber fabrication technology,
various fibers working in 2 micron region are commercially available. Two micron fiber MOPA systems are more
attractive for researchers due to their compactness, good thermal dissipation and high efficiency. A 2 micron
master-oscillator-power-amplifier (MOPA) system was built. The seed oscillator was a plano-concave straight cavity.
YAP Laser crystals with 4% and 5% thulium-doped concentration were used in our experiments. 1.5% and 3% output
couplers were used. 442mW output power at 1.99μm was obtained with the 4% thulium-doped Tm:YAP crystal when
the launched pumping power is 2.7W. The seed oscillator is coupled into a 4.5-meter-long double-cladding LMA Tm<sup>3+</sup>
and Al<sup>3+</sup> co-doped fiber. The fiber diameter is 25 μm and NA is 0.1. 6.13W CW amplified output signal power was
obtained when the launched pumping power was 60W.