Study of a 4f phase imaging system relying on thermally induced phasemodulation in absorbing organic dyes

• Main Authors: Zhe-an He, 何哲安
• Other Authors: Tai-Huei Wei
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/86216929610841634749

碩士 === 國立中正大學 === 物理所 === 97 === Phase contrast microscopy has a distinctive feature, comparing to the conventional ones, in that it can observe transparent living cells in their natural state. Mainly, the phase of the surrounding wave is modified by π/2 or –π/2 with a phase plate but the phase of the diffracted wave is maintained. Therefore, recombination of the surrounding and diffracted waves causes a phase contrast at the exit surface of the phase plate and makes the structural detail of a transparent specimen visible in the background of the biological image. In this thesis, we set up our experiment as a 4f system with a CW laser at 532 nm. The DDLC (dye doped liquid crystal) film and the cuticle of an onion are used as the phase plate and the specimen respectively. The dye we used is Methyl Red (MR). Not only can MR absorb laser at 532 nm but also decline the transmittance of the background. By absorbing the laser, MR transfers the energy to his neighboring liquid crystal molecules. The temperature of the DDLC film is therefore increased and results in a refractive index change. Thus the DDLC film varies the phase of the surrounding wave by π/2 when it reaches a certain amount of absorption and leaves the phase of the diffracted wave unchanged. As a result, we produced a higher contrast image of the specimen by recombining the surrounding and diffracted wave. Also, we studied the influence of the absorption of the background on the contrast by changing the concentration or the thickness of DDLC film.