## 4 Conclusions  
The development of the dye-doped nematic liquid crystal (NLC) optical power limiter (OPL) presented in this study marks a significant advancement in protective technologies for CCDs against high-intensity light exposure. This innovative approach, employing a twisted nematic cell configuration with integrated polarizers, capitalizes on the synergistic effects of reorientational and thermal nonlinearities inherent in NLCs. The results unequivocally demonstrate that the device is effective in modulating the transmission of intense light and efficient in its responsiveness across different light intensities, particularly in the visible spectrum, where CCD cameras are most vulnerable. A pivotal finding of our investigation is the ability of the NLC-based OPL to operate without external electric fields, a common requirement in traditional electro-optical systems. This feature significantly simplifies the  
Figure 6: **(a,b)** The proposed arrangement of the CCD camera and the NLC power limiter; **(c)** The object viewed by the camera, with the aperture in the central part of the image (marked by a dotted line), according to the configuration in **(a)**; **(d)** The image obtained by the CCD camera (fully saturated) when the CCD matrix is directly illuminated with a beam of about 2 mm width, \(\lambda\) = 532 nm, and power of P = 200 mW; **(e-g)** images of the object taken by a CCD camera combined with a liquid crystal optical power limiter, recorded at different moments from beam exposition: t\({}_{1}\) < 30 ms, t\({}_{2}\) = 67 ms, and t\({}_{3}\) = 350 ms.  
system architecture, reducing potential failure and maintenance points, thus enhancing reliability and durability in demanding operational environments such as military and aviation applications. Using green light in our experiments further aligns this study with real-world applications, where the peak sensitivity of CCDs to this wavelength amplifies the risk of damage and operational disruption. Moreover, the successful integration of absorbing plastic sheet polarizers not only contributed to a substantial reduction in the threshold power necessary for activation but also proved critical in fine-tuning the device's optical properties to achieve optimal performance. This aspect of our research underscores the potential for scaling the technology to accommodate a range of wavelengths, suggesting broader applications beyond those demonstrated. In a linear regime (low input intensities), we observe the transmission in a range from 30% to 60%. Using an unfocused laser beam, the switch-off power is as low as 60 mW \(\div\) 120 mW depending on the NLC material and dye, which is at least one tenth of the value for the undoped TN sample without absorbing polarizers. The response time of the proposed structure is about several tens of milliseconds, while the turn-on time is less than 20 milliseconds. The optical structure demonstrated operates without the need for an external power source and effectively protects the CCDs from the intense optical beam in an angle of incidence range as wide as \(\pm\)30\({}^{\circ}\). Furthermore, the long-term operational reliability of the proposed NLC optical power limiters has been verified over a period of one year. This has revealed that the operational properties are in excellent agreement with the freshly prepared NLC samples. The current technology for NLC-based optical devices, such as LCD displays, is well established and offers numerous advantages for implementing the proposed solution. It is also pertinent to highlight that despite the perception that liquid crystal mixtures--a chemical cocktail comprising several organic compounds--may be hazardous, extensive studies conducted by Merck have demonstrated otherwise [56; 57]. Liquid crystals found in LCDs, including those that may be utilised in NLC OPL, are non-hazardous and do not present an unreasonable risk to human health or the environment.