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Analysis of a Laser Direct Writer with an Acousto-optic Modulator Employed for Dose Gray-scaling
박종락,Youngsik Kim,Tom D. Milster 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.51
We have studied a laser direct writing system for the fabrication of gray-scale diffractive optic elements in terms of its system characteristic curve that can be understood as a composite function of a characteristic curve for an acousto-optic modulator employed for dose gray-scaling and that for a photoresist used for continuous profile formation. A mathematical analysis method was developed and applied to retrieve the two constituent characteristic curves for the acousto-optic modulator and the photoresist from the system characteristic curves. The validity of the results was confirmed through comparison with direct measurements.
Homodyne time-of-fl ight acousto-optic imaging for low-gain photodetector
Ahiad R. Levi,Yoav Hazan,Aner Lev,Bruno G. Sfez,Amir Rosenthal 대한의용생체공학회 2023 Biomedical Engineering Letters (BMEL) Vol.13 No.1
Acousto-optics imaging (AOI) is a hybrid imaging modality that is capable of mapping the light fluence rate in deep tissue by local ultrasound modulation of the diffused photons. Since the intensity of the modulated photons is relatively low, AOI systems often rely on high-gain photodetectors, e.g. photomultiplier tubes (PMTs), which limit scalability due to size and cost and may significantly increase the relative shot-noise in the detected signal due to low quantum yields or gain noise. In this work, we have developed a homodyne AOI scheme in which the modulated photons are amplified by interference with a reference beam, enabling their detection with a single low-gain photodetector in reflection-mode configuration. We experimentally demonstrate our approach with a silicon photodiode, achieving over a 4-fold improvement in SNR in comparison to a PMT-based setup. The increased SNR manifested in lower background noise level thus enabling deeper imaging depths. The use of a fiber-based configuration enables the integration of our scheme in a hand-held AOI probe.
광음향 변조기의 단일 경로와 이중 경로를 동시에 사용한 이종 간섭계 방식의 레이저 도플러 진동계
오현석(Hyun Seok Oh),정연홍(Youn Hong Jeong),조재흥(Jae Heung Jo) 한국산학기술학회 2022 한국산학기술학회논문지 Vol.23 No.3
한 대의 광음향 변조기에 대한 단일 경로와 이중 경로를 각각 통과한 서로 다른 2개의 반송 주파수를 갖는 물체빔 2개와 기준광을 사용하여 서로 다른 두 위치에서 발생하는 진동수를 동시에 측정하는 3개 빔 이종 간섭계 방식의 레이저 도플러 진동계(LDV)를 제안한다. 이러한 LDV의 이론적 배경을 위하여 3개의 서로 다른 반송주파수가 반공 주파수가 서로 다른 2개의 물체 빔과 기준광을 서로 간섭시키는 간섭이론을 기술한다. 3개 빔 이종 간섭계 방식의 레이저 도플러 진동계의 변조 주파수가 40 ㎒인 광음향 변조기를 한 번 통과한 물체빔과 두 번 통과한 물체빔의 반송 주파수는 각각 40 ㎒와 80 ㎒이며, 이 값들을 이용하여 LDV의 이론을 통하여 2군데의 물체 진동수를 동시에 감지할 수 있는 이론적 근거를 확인하였다. 논문에서는 이러한 헬륨네온 레이저와 광음향 변조기 1대를 사용하여 두 물체빔을 사용하여 동시에 두 지점의 서로 다른 진동주파수를 측정할 수 있는 것을 실험적으로 확인하였다. 이 방법을 확장하면 물체의 서로 다른 2개 이상의 측정지점에 대한 진동 주파수를 쉽고 간단하게 측정할 수 있다. We propose a laser Doppler vibrometer (LDV) of three beams heterodyne interferometer type with a photodetector composed of two object beams having different carrier frequencies. With the single and double-passes of an acousto-optic modulator (AOM) and a reference beam, the LDV simultaneously measures two different vibrational frequencies generated at two positions. To build up the theoretical background, we describe the interference theory using a reference beam and two different object beams of different carrier frequencies. The carrier frequencies of two object beams passing through the single and double-passes in the AOM are 40 ㎒ and 80 ㎒, respectively, and the modulation frequency of the AOM is 40 ㎒. Using these frequency values in the LDV theory, we confirm the theoretical justification of a laser Doppler vibrometer (LDV) of three beams heterodyne interferometer type. In addition, this paper confirms, through simulation and experiment, that the LDV can detect two different vibrational frequencies caused by simultaneous vibrations at two different points. Thus, this method can be utilized simply and readily to observe more than two different vibrational frequencies of objects.