RESULTS AND DISCUSSION (CONT’D) LASER ABSORBING MATERIALS Leong Feng Ping Angela 1 , Ke Meicong 1 , Yang Qian Asarelah 1 and Koh Yaw Koon 2 1 NUS High School of MathemaKcs and Science, 20 ClemenK Avenue 1 Singapore 129957 2 DSO NaKonal Laboratories, 20 Science Park Drive Singapore 118230 PURPOSE The solgel process has been used to produce silica glass doped with samarium (Sm 3+ ) ions as the base material. The Sm 3+ ion shows great absorpKon around 1064 nm as the difference in energy level between its orbitals corresponds to the energy of light with a wavelength of 1064 nm. We aimed to determine the op8mum thickness and hea8ng protocol for samariumdoped glass to achieve maximum absorp8on efficiency at a wavelength of 1070nm. CONCLUSION • HeaKng increases absorpKon efficiency at 1070 nm for all three thicknesses. • HeaKng appears to reverse the relaKonship between thickness of the film and absorpKon efficiency, such that thinner films display higher absorpKon efficiencies. A thinner layer of silica gel could be used to achieve higher laser absorp8on, simply by hea8ng during the solidifying process. This allows huge cost savings when scaled up for use in the field. RESULTS AND DISCUSSION FUTURE WORK • Verify the relaKonship between film thickness and absorpKon efficiency with a larger range of thicknesses, and analyse the transmibance/absorbance spectrum in greater detail • Test a wider range of hea8ng protocols, to opKmise heaKng protocols for specific wavelengths and for other laserabsorbing materials • OpKmise absorpKon efficiency by adjusKng both gel thickness and samarium concentraKon: electrostaKc repulsion exists between the Sm 3+ ions within the silica, thus the op8mal concentra8on of samarium is the tradeoff between the maximum absorpKon density of Sm 3+ and minimum repulsion between the Sm 3+ ions. • Study the use of samariumdoped silica gel for the absorp8on of lasers emiNed at other wavelengths, as the greatest drop in transmibance occurs at 1400 . ACKNOWLEDGEMENTS This work was supported by the Young Defence ScienKsts Programme (YDSP), Ministry of Defence, Singapore. 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Nano LeSers 12, 1443 (2012) INTRODUCTION The ubiquity of laserguided devices in the military has compelled the evoluKon of laser concealment and laserjamming techniques. Passive laserabsorbing materials can be divided into organic materials and inorganic materials, of which organic materials are more versa8le, but are unstable under UV light and involve complicated synthesis methods. The inorganic metamaterial is of a parKcular interest because it passively interferes with electromagneKc (EM) waves and is able to absorb at various wavelengths, but much research has focused on broadband absorp8on and on the paNerning of base materials. However, the most common laser in military use – the Nd:YAG laser – is emibed at a specific wavelength of 1064 nm. EXPERIMENTAL RelaKve transmibance in arbituary unit (A.U.) of samariumdoped silica gel of different thickness under different heaKng protocol 100 μm 200 μm 300 μm Airdried 89.426 A.U. 88.818 A.U. 88.301 A.U. Ovendried 85.017 A.U. 86.301 A.U. 87.148 A.U. % increase due to heaKng 5.186% 2.917% 1.323% Sm 3+ Samarium ions integrate into the spaces within the silicate lamce Spectrophotometer Results (1a) (1b) RelaKve transmibance in arbituary unit (A.U.) against wavelength (nm) of samples of different thickness when (a) airdried and (b) overdried RelaKve transmibance in arbituary unit (A.U.) against wavelength (nm) of airdried and oven dried samples of different thickness (a) 100 μm (b) 200 μm (c) 300 μm (2b) (2a) (2c) Absorp8on efficiency of airdried samples increases with increasing thickness The thicker the silica gel, the longer the EM wave takes to propagate through the gel, increasing the likelihood of the photons being absorbed by the electrons of the Sm 3+ ions. Absorp8on efficiency of overdried samples decreases with increasing thickness HeaKng the silica sol increases the kineKc energy of Sm 3+ ions and atoms of the silicate lamce, causing Sm 3+ ions to break and migrate to other locaKons within the lamce while forming new bonds HeaKng may alter the structure of the Sm 3+ doped silica gel such that its opKcal properKes are changed. • At all wavelengths, ovendried silica gels absorb a higher percentage of EM wave than airdried silica gels of the same thickness. • Airdried samples show a sharp drop in transmibance – a local peak of the absorbance spectrum – just aner 1070nm. • The heaKng protocol shins the peak of the absorpKon spectrum towards shorter wavelengths and towards 1070 nm, but the peak becomes less pronounced. • Maximum absorpKon of waves with wavelength 1070 nm is achieved at a thickness of 300 μm. • The increase in absorpKon efficiency imparted by furnace heaKng decreases with increasing thickness. ② IncorporaKon of samarium ions Image taken from: hbp :// upload.wikimedia.org/ wikipedia/commons/thumb/ 4/4b/Silica.svg/220px Silica.svg.png with NH 4 OH (Literature) sKrring without NH 4 OH(Ours) sKrring Casting & Gelation: Preparation of Sm 2 O 3 sol: Dry at room temperature for 24 hours. Heated in a furnace at an increase of 5 o C/ min and held at 650 o C for 15 mins before cooling to room temperature. Dry at room temperature for 24 hours. Characterization Both the heated and unheated samples were characterized using a UVVISNIR spectrophotometer (UV3600, Shimadzu) at the near infrared region (900nm – 1200nm). Mica is a silicate mineral chemically inert and stable when exposed to electricity, light, moisture, and extreme temperatures. Optical and chemical properties of mica unlikely to be affected by contact with the silica gel or heating process. white precipitate homogeneous Mechanism ①FormaKon of silicate Image taken from: The Sol-Gel Preparation of Silica Gels A. M. Buckley and M. Greenblatt Journal of Chemical Education 1994 71 (7), 599 Monday, March 11, 13