Stimulated emission depletion (STED) microscopy had greatly enhanced our ability to explore the microscopic world, which can provide sub-diffraction resolution. The high resolution of STED depends on the shape of the depletion patterns with the center is a null intensity. Optical aberrations were the most important factor which affects the shape of the depletion patterns. In this paper, the influences of aberrations modes on the performance of depletion patterns in STED microscopy were studied by numerical simulation and experiment using Zernike polynomials. Simulation results show that the coma, trefoil, astigmatism and spherical had the largest effect on depletion patterns. Also, distortion and blurring of the image will increase with multiple wavefront aberrations. Finally, the simulation results are verified by experiments based on space light modulator (SLM). The study provides a scientific basis for designing a STED system, and has important guiding significance in both theory and practice.
Terahertz (THz) wave has great potential applications in the fields of security, material, biomedicine and nondestructive testing, due to its low energy, high penetrability, nondestructive property and fingerprint characteristics. In this paper, a high-performance objective system was presented and designed for THz camera. The THz objective system has an effective focal length of 39.5 mm, a F-number of 0.9, a full field angle of 24°, and a working band covering 70 - 200 μm (frequency range from 1.5 to 4.28 THz). In the system, a coaxial structure consisted of three spherical lens and a piece of aspherical lens was used. The design result shown that the root mean square radius (RMS Radius) of the sport diagrams were basically within the airy disk radius. At a cut-off frequency of 5 lp/mm, the modulation transfer function (MTF) values in the full field of view were above 0.22, which was close to the diffraction limited curve. In summary, the designed objective system has good imaging quality and high resolution, which can meet the performance requirements of large-field THz imaging systems, and has good application prospects in THz microscopic imaging.
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