|Shilts, Patrick - US Department Of Agriculture (USDA)|
|Motabar, Payam - US Department Of Agriculture (USDA)|
|Tasch, Uri - University Of Maryland|
Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2015
Publication Date: 4/1/2015
Citation: Shilts, P., Motabar, P., Lefcourt, A.M., Kim, M.S., Tasch, U. 2014. Homogenization optics to improve detectability of a fluorescence response to a single laser pulse: Detection of feces on apples. Transactions of the ASABE. 57(2):615-622.
Interpretive Summary: Fecal contamination of produce is a known food safety risk. Consequently, the development of instrumentation to identify fecal contamination on produce in the field would allow pickers to bypass those areas. Fluorescence responses of fecal material to ultraviolet (UV) illumination is the preferred method of detection. This poses a dilemma for field applications because the fluorescence responses can be masked by sun light. A potential solution to this problem is to use a pulsed UV laser beam to elicit the fluorescence responses. However, this requires an expanded laser beam in order to illuminate the produce surface area being tested. One method for expanding the beam is to use homogenizing optics. In this study, we describe a method to homogenize the expanded laser beam. Testing of new method confirmed that the homogenizing optics approach was successfully, allowing for reliable detection of fecal material on produce surfaces. These results will be of interest to agricultural scientist working in the areas of food safety and imaging, as well as food safety personnel in general.
Technical Abstract: Fecal contamination of produce is a known food safety risk. Measuring fluorescence responses to UV excitation is an established method for detecting such contamination. One measurement system utilizes a pulsed UV laser to induce a fluorescence response from fecal material and a gated intensified camera to detect the response. A particular advantage of this measurement system is the ability to detect a response regardless of ambient illumination. This system requires that the laser pulse be expanded to illuminate the area being imaged. In the past, simple optical systems consisting of a series of a few lenses were used to expand the laser beam. In this study, the value of incorporating a light pipe in the expansion optics to homogenize the excitation illumination was investigated. Tests using uniform fluorescent targets demonstrated that variability in illumination intensity for individual pixels was reduced across sequential images, each captured using a single laser pulse for illumination. The homogenizing optics also reduced the measured variation in responses across pixels in single images. Tests using apples contaminated with dilutions of manure were less definitive. Still, the homogenizing optics dramatically increased detection rates for 1:1000 dilutions and increased sensitivity in terms of the relatively magnitude of the measured intensity of fluorescence responses for 1:2 and 1:20 dilutions. It is recommended that the homogenizing optics be used for expansion of a pulsed laser beam used to excite a fluorescence response from a target.