Significance With the rapid development of laser technologies, the number of laser weapon equipment is increasing. At the same time, human eyes, photoelectric detection equipment, and optical systems are being exposed to strong laser environment and are vulnerable to laser attacks. It is an urgent problem to ensure that these devices have anti-attack capability based on normal operation. Consequently, it is paramount to develop a laser protection technology.
Based on the working principle, the laser protection technology can be divided into two types. One is based on the linear optical principle, such as absorption-type filter, reflection-type filter, and coherent filter. The other is based on the nonlinear optical (NLO) principle—also known as optical limiting (OL)—such as nonlinear absorption-, scattering-, and refraction-type optical limiters. In addition, there are thermally induced phase-change materials and liquid-crystal materials, etc. The OL technology can combine high transmittance to weak light and low transmittance to strong light at the same wavelength. In addition, it has obvious advantages in the protection against high-energy, continuous broadband laser spectra, and ultrafast response time. Moreover, it is one of the materials with high practical application value in the field of laser protection.
Progress Various materials, such as graphene, transition metal dichalcogenide (TMDC), black phosphorus (BP), carbon nanotube, phthalocyanine, and porphyrin, can be used to fabricate optical limiters. This study focuses on the progress of two-dimensional (2D) nonlinear optical limiting materials, such as graphene, TMDC, and BP, applied in the aspect of laser protection.
In 2009, Wang et al. first reported the OL characteristics of high-quality graphene (
Feng et al. investigated the NLO and OL properties of graphene families, including graphene oxide nanosheets, graphene nanosheets (GNSs), graphene oxide nanoribbons (GONRs), and graphene nanoribbons (GNRs), using 532 nm and 1064 nm nanosecond lasers (
Dong et al. reported the NLO properties of TMDC nanosheet dispersions, including MoS2, MoSe2, WS2, and WSe2, using nanosecond laser pulses at 1064 nm and 532 nm (
Li et al. synthesized mono- and multilayer MoS2 triangular islands using a seeding method via chemical vapor deposition (
Huang et al.investigated the wavelength- and pulse-duration-dependent SA properties of BP by a femtosecond laser pulse at 1030 nm/515 nm and a nanosecond laser pulse at 1064 nm/532 nm (
Conclusion and Prospect In this paper, we have introduced the basic concept of a laser protection technology, summarized several laser protection schemes, and illustrated the mechanism of laser protection technology based on the NLO principle. Moreover, we have introduced the research progress of three types of 2D NLO materials—graphene, TMDC, and BP—in term of laser protection. In summary, these materials exhibit OL characteristics in the range of visible to near-infrared bands. For ns-pulsed laser, laser protection is mainly induced by nonlinear scattering, while for fs-pulsed laser, it is dominated by two-photon absorption. Under the same experimental conditions, the OL properties of three materials from strong to weak orders are TMDC, graphene, and BP. In addition, the covalent modification can improve the dispersion of 2D nanomaterials as well as their OL and NLO properties. However, the development of laser protection devices based on these materials is still in the research stage, and they are yet to be practicalized. For 2D nanomaterials, many problems still remain, such as: 1) the materials have a strong aggregation effect, leading to poor dispersion; 2) the problem of realizing the precise control of the layer number and size of 2D materials makes it difficult to achieve low-cost and large-scale material fabrications. In the future, we need to focus on these materials to design and fabricate high-quality covalent chemically modified 2D nanomaterials as well as develop ideal OL devices with broad protective spectral bands, low input thresholds, high linear transmittance to weak radiation, fast responses, and large damage thresholds.