Conditions for effective application of passive speckle reduction methods and decoherent focusing method in laser illumination systems

• Datum: 2025
• Hauptverfasser: Лапчук, А. С., Пригун, О. В., Манько, Д. Ю., Горбов, І. В., Бородін, Ю. О.
• Format: Artikel
• Sprache: Ukrainisch
• Veröffentlicht: Інститут проблем реєстрації інформації НАН України 2025
• Schlagworte: speckle suppression; laser projector; decoherence; decoherent focusing system; passive system; laser illumination
• Online Zugang: http://drsp.ipri.kiev.ua/article/view/345498
• Назва журналу: Data Recording, Storage & Processing

This study presents a comprehensive investigation of passive speckle reduction methods in laser illumination systems, which utilize two key factors simultaneously: the imperfect temporal coherence of laser radiation and angular diversity created by the optical system. Special attention is given to analysing the conditions for independent operation of these factors to achieve maximum efficiency in reducing spatial coherence. An innovative optical system design for decoherent focusing is proposed, consisting of a two-dimensional array of rectangular microprisms with variable heights integrated with a pair of crossed single-element cylindrical Fresnel lenses. Computer simulations demonstrate that this system can effectively transform a collimated Gaussian beam into a high-quality, uniformly illuminated rectangular spot, even at a substantial numerical aperture (NA = 0,2). Additionally, a simplified flat version of the system using a single lens is proposed while maintaining all key characteristics. The fundamental limitation of passive methods related to the line spectrum of laser diodes is thoroughly examined, showing it significantly reduces the number of decorrelated sub-beams. The experimental results prove that dynamic current modulation within ±15 % of the nominal value transforms the discrete spectrum into a quasi-continuous one. This effect enables generation of virtually unlimited statistically independent laser beams, opening new possibilities for high-quality illumination systems. For practical implementation in laser projectors, a critical parameter is established — the intensity integration time must not exceed the temporal resolution of human vision (approximately 20–40 ms). The obtained results have significant practical potential for developing new generations of laser illumination systems with minimized speckle effects, particularly relevant for precision projection technologies, medical diagnostics, and industrial applications. The work includes detailed analysis of optical schemes, mathematical modeling results, experimental data, and practical recommendations for implementing the proposed technological solutions. The presented results substantially expand the capabilities of passive speckle reduction methods and offer a novel approach to designing laser illumination systems. Tabl.: 3. Fig.: 14. Refs: 32 titles.