Laser Interaction with Grass Tissues

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Laser Interaction with Grass Tissues
Kim, Jaehun
Ki, Hyungson
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Graduate School of UNIST
This thesis has three chapters as first chapter: UV, Visible and IR light interaction with grass-tissues, second chapter: IR light with different water absorption coefficient interaction with grass-tissues and third chapter: laser lawn mowing system. Fist chapter, we investigated how UV, Visible and IR light affectgrass tissues. Grass tissues are composed mainly of pigments and water. Chlorophyll plays the role of the photosynthesis and it is not only the green pigment but it also absorbs visible light(blue and red) well. The water content of grass tissues helps the photosynthesis with carbondioxide and it can react well with absorbed IR light. UV light canbreak the chemical bonding of materials more easily than longerwavelengths (i.e. Visible and IR regimes), since the shorter wavelengths have higher electrical potential than longer wavelengths. 355nm (UV), 532nm (Visible) and 1064nm (NIR) wavelengths generated by a picosecond pulsed laser were used in the experiment. Thus, we made a process map of each wavelength and we analyzed the difference between the three wavelength regimes by using a scanning electron microscope and an optical microscope.From a process map of each wavelength, we found that the 355nm is most effective energy transfer to grass-tissues than 532nm and 1064nm wavelength and 1064nm (IR) light can reduce the damage of grass-tissues because of water absorption coefficient dominant. Therefore, we believed that chlorophyll dominant case and water dominant case have difference interaction mechanism. The chlorophyll dominant case makes directly energy of light transfer to grass-tissues then grass-tissues ablated directly. However, the water dominant case makes responses (carbonization, through-cut, partial-cut and decoloration) by heat of around absorbed area from water evaporation in grass-tissue or on surface of grass. In chapter II,Er:YAG (2.94μm) and CO2 (10.6μm) laser interaction with grass tissues had investigated. 2.94μm and 10.6μm light, Infrared (IR) regimes, laser have high water absorption coefficient as 12000 and 860 respectively. The sample thickness (grass thickness) is around 110μm. Since we can believe that the water content can reduce damage to grass-tissues from results previous Chapter I, the effect of water content in grass tissues had investigated in this chapter as how differently affect grass tissues as different water absorption coefficient at 2.94μm and 10.6μm wavelength cases. Plus, we investigated beam size effect and how seasonally affect grass-tissues (water concentration). Therefore, some results were found. Even though same intensity and interaction time, response is different as large beam size makes only carbonization response. 2.94μm with high water absorption coefficient light made faster response change than 10.6μmlight at using same beam size (1mm). Chapter III, Typical lawn mower is cut the lawn by contact method such as rotate blade and its equipment used foil fuel engine. From these reason, typical lawn mower can make noise seriously and dangerous and some pollution. However, laser lawn mower is using non-contact method and electrical power. Thus, it can be more quite, safety and little pollution. Furthermore, from previous results Chapter I and II, developed process maps of each laser can be used to manufacturing laser lawn mowing system. In this chapter, we will introduce concept of laser lawn mowing system and suggest optical-setups to cut-well and advantage and disadvantage of each wavelengths.
Mechanical Engineering
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