Labardi M, Tikhomirov O, Ascoli C, Allegrini M
INFM-CNR polyLab, Dipartimento di Fisica Enrico Fermi, Università di Pisa, Largo B. Pontecorvo 3, I-56127 Pisa, Italy.
Rev Sci Instrum. 2008 Mar;79(3):033709. doi: 10.1063/1.2899146.
A quadrature optical detection technique, based on polarized balanced-homodyne interferometry, has been developed for specific application to apertureless near-field scanning optical microscopy (ANSOM). With such technique, multiplicative background interference, inficiating quantitative optical imaging in standard homodyne-based ANSOM, can be suppressed. Periodic modulation of interferometric optical phase, typically employed in heterodyne-based ANSOMs even to such purpose, is not needed in the present configuration. Homodyne detection also facilitates detection of harmonic components of the ANSOM optical signal at the probe/sample distance modulation frequency, necessary for near-field discrimination and suppression of artifacts. Furthermore, since amplitude signal is not affected by phase fluctuations generated in the optical path of the interferometer, an optical fiber could be included in one interferometer arm, to couple the ANSOM head to the detection system, obtaining improved versatility of the instrument. A demonstration of the interferometer performance is given by a test confocal optical scan of a mirror surface. This technique, as applied to near-field microscopy, is anticipated to provide absolute values of optical contrast not depending on background interference and topography artifacts.
一种基于偏振平衡零差干涉测量法的正交光学检测技术已被开发出来，用于无孔径近场扫描光学显微镜（ANSOM）的特定应用。采用这种技术，可以抑制在基于零差的标准ANSOM中影响定量光学成像的乘法背景干扰。在本配置中，不需要像基于外差的ANSOM中通常甚至为此目的所采用的干涉光学相位的周期性调制。零差检测还便于在探针/样品距离调制频率下检测ANSOM光信号的谐波分量，这对于近场辨别和伪像抑制是必要的。此外，由于幅度信号不受干涉仪光路中产生的相位波动的影响，可以在一个干涉仪臂中包含一根光纤，将ANSOM探头与检测系统耦合，从而提高仪器的通用性。通过对镜面进行共焦光学扫描来演示干涉仪的性能。预计这种应用于近场显微镜的技术将提供不依赖于背景干扰和形貌伪像的光学对比度的绝对值。
