Apparatus for illuminating the tip-sample interface of an atomic force microscope

An apparatus for the delivery of radiation to the tip-sample interface of an atomic force microscope (AFM) is demonstrated. The pulsed light delivery system (PLDS) was fabricated to probe photoinduced conformational changes of molecules using an AFM. The system is 67 mm long, 59 mm wide, and 21 mm high, leaving clearance to mount the PLDS and a microscope slide coated with a thin film of photoactive molecules beneath the cantilever tip of a stand-alone AFM. The PLDS is coupled into a fiber pigtailed Nd:yttrium-aluminum-garnet frequency doubled laser, operating at a wavelength of 532 nm. The radiation delivered to a sample through the PLDS can be configured for continuous or pulsed mode. The maximum continuous wave power delivered was 0.903 mW and the minimum pulse width was 12.3 mus (maximal 401 mus), corresponding to a minimal energy of 0.150 nJ (maximal 362 nJ), and had a cycle duration of 10.0 ms. The PLDS consists of micro-optical components 3.0 mm and smaller in diameter. The optical design was inspired by the three-beam pickup method used in CD players, which could provide a method to focus the pulse of light onto the sample layer. In addition, the system can be easily modified for different operational parameters (pulse width, wavelength, and power). As proof that the prototype design works, we observed a photoinduced 'bimetallic' bending of the cantilever, as evidenced by observing no photoinduced bending when a reflective-coated cantilever was replaced by an uncoated cantilever. Using the apparatus will allow investigation of many different types of molecules exhibiting photoinduced isomerization. (C) 2003 American Institute of Physics.