To meet the specific needs or improve the system’s energy efficiency, it is necessary to integrate the beam into a specific intensity distribution beam. This paper establishes a set of rules based on the mixed-region amplitude freedom (MRAF) algorithm, and a beam shaping algorithm is proposed to calculate the intensity distribution by setting the energy efficiency. Simulation results show that compared with the traditional Gerchberg–Saxton (GS) algorithm, the convergence effect improved by one to two orders of magnitude after abandoning controlling a small part of the energy; compared with the MRAF algorithm, the energy efficiency converged to the preset target value, in addition, the energy efficiency is higher under the same convergence intensity. This algorithm provides a new path for shaping in femtosecond laser processing technology.
In inertial confinement fusion laser device, the disposable debris shield is necessary to protect expensive optical elements from the contaminations of target debris when high-energy PW laser was focused in the terminal focusing system. While the shield plate will have a very important impact on the focusing quality. In this paper, the design of debris shield, in high-energy PW focusing system, is studied by optical transmission theory, and the design parameters, such as PV value of wavefront, thickness and installation position of shield plate, are optimized. If 95% of the focal spot energy is concentrated within 10DL, the B-integral introduced by the debris shield should not exceed 8.5 rad when the plate is placed at 0.1f from the parabolic mirror. When the laser power is 1PW, the installation position of 3mm shield cannot exceed 0.29f. The influence of wavefront PV value on energy concentration of focal spot is little. A 3mm shield plate has good damage resistance on light field modulation when its size over 350μm. And the thinner the thickness is, the better the resistance is. This work is important for the arrangement and optimization of disposable debris shield in high-power PW laser focusing system.
We demonstrated a broadband Nd: glass laser amplifier with controllable gain bandwidth in experiment, which is expected to be used in high energy low coherent laser amplifier system. A birefringent crystal for spectral filtering in regenerative laser amplifier was designed and proposed, and the parameters of birefringent crystal was optimized in simulation. The birefringent crystals with different bandwidths were designed by this method. The laser amplification output with different gain bandwidths of 6~10 nm was realized, which was also verified by experiments. This broadband Nd: glass laser amplifier is expected to be used in large scale broadband laser amplification system, and provides important technical support for a new type of broadband tunable nanosecond high-power laser facility.
High repetition rate slab amplifier (HRRSA) is extraordinarily indispensable for the future fusion power plant, ultra-short laser, laser weapon, and so on. Thermal controlling is the decisive factor for the repetition rate and the output energy of the slab amplifier. For larger clear aperture HRRSA, flash-lamp pumped slab amplifier based on neodymium phosphate glass (Nd:glass) is chosen with the liquid cooling. The liquid coolant circulates across the Nd:glass and takes off the thermal induced in the pumping process. A novel liquid coolant (Series A) whose refractive index is the same with Nd:glass is proposed to alleviate the wavefront distortion induced by thermal. The chemical stability of the liquid coolant under high energy flash-lamp irradiation with 200 shots and under the irradiation of a 1053nm laser with 19 hours and 37 hours are experimented. The results show that the chemical stability of the liquid coolant is stable under irradiation.
KEYWORDS: Laser damage threshold, Laser induced damage, Optical components, Near field optics, Thin films, Laser sources, Superluminescent sources, Near field, High power lasers, Modulation
An accurate evaluation method with an amplified spontaneous emission (ASE) as the irradiation source has been developed for testing thin-film damage threshold. The partial coherence of the ASE source results in a very smooth beam profile in the near-field and a uniform intensity distribution of the focal spot in the far-field. ASE is generated by an Nd: glass rod amplifier in SG-II high power laser facility, with pulse duration of 9 ns and spectral width (FWHM) of 1 nm. The damage threshold of the TiO2 high reflection film is 14.4J/cm2 using ASE as the irradiation source, about twice of 7.4 J/cm2 that tested by a laser source with the same pulse duration and central wavelength. The damage area induced by ASE is small with small-scale desquamation and a few pits, corresponding to the defect distribution of samples. Large area desquamation is observed in the area damaged by laser, as the main reason that the non-uniformity of the laser light. The ASE damage threshold leads to more accurate evaluations of the samples damage probability by reducing the influence of hot spots in the irradiation beam. Furthermore, the ASE source has a great potential in the detection of the defect distribution of the optical elements.
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