{"id":5165,"date":"2026-01-20T16:36:41","date_gmt":"2026-01-20T15:36:41","guid":{"rendered":"https:\/\/www.fresnel.fr\/wp\/?post_type=animation&p=5165"},"modified":"2026-01-20T16:37:05","modified_gmt":"2026-01-20T15:37:05","slug":"xiangyi-li-phd","status":"publish","type":"animation","link":"https:\/\/www.fresnel.fr\/wp\/en\/animation\/xiangyi-li-phd\/","title":{"rendered":"Xiangyi LI, PhD"},"content":{"rendered":"

Xiangyi LI will defend her thesis entitled “Widefield linear and non-linear optical microscopies using random illumination and temporal focusing<\/strong><\/em>” on Thursday, January 22nd at 02:00 p.m.<\/strong> in room Pierre Cotton of Institut Fresnel.<\/p>\n

 <\/p>\n

Composition of the Jury :<\/strong>
\n– Marc GUILLON, SPPIN, Reviewer
\n– Eirini PAPAGIAKOUMOU, Institut De La Vision, Reviewer
\n– Hilton BARBOSA DE AGUIAR, Kastler Brossel Laboratory, \u00a0 Examiner
\n– Herv\u00e9 RIGNEAULT, Institut Fresnel, Examiner
\n– Martin OHEIM, SPPIN, Jury President
\n– Anne SENTENAC, Institut Fresnel, Thesis supervisor<\/p>\n

 <\/p>\n

Abstract :<\/strong> Wide-field optical microscopy, in which the whole sample is illuminated in one shot and the image is recorded on a camera, is widely used for observing micrometric and submicrometric structures due to its speed, robustness, and minimal impact on samples. However, it suffers from two major limitations: limited transverse resolution (at best, half the wavelength) and, more critically, a lack of optical sectioning. Because the sample is also illuminated in depth, light from out-of-focus planes degrades image contrast, making the technique ineffective for thick samples. This thesis explores how random speckle illuminations and temporal focusing can introduce optical sectioning in wide-field microscopy, particularly for one and two-photon excitation fluorescence microscopy and for nonlinear imaging. First, the work investigates Random Illumination Microscopy (RIM) for one-photon fluorescence. RIM is a widefield microscopy method that uses the variance of mul-tiple images acquired under different speckle patterns to numerically reconstruct a super-resolved, optically sectioned image. While RIM was originally developed for 2D imaging, this thesis extends the algorithm to 3D, introducing an iterative deconvolu-tion procedure tailored for images with few optical planes. The 3D approach yields better resolution and contrast than slice-by-slice 2D reconstruction. Next, the study addresses two-photon excitation fluorescence microscopy (2PM), which typically relies on scanning a tightly focused beam for sub-micrometer res-olution and optical sectioning. However, the scanning modality proves slow when imaging large fields of view. To overcome this issue, we extended RIM principles to two-photon wide-field microscopy (2PE-RIM) . We theoretically and experimentally demonstrate an improved resolution and optical sectioning. A second approach con-sisted in developing a novel excitation scheme for the scanning modality. We showed that a focused speckled beam is able to form a 2P excitation volume with a transverse width and axial width of a few micrometers. This illumination scheme is susceptible to provide faster scans of large fields of view (at the cost of a reduced resolution). In the third chapter, we also explore the potential of Temporal Focusing (TF), for generating optical sectioning in non-linear widefield microscopy. To create a tem-porally focused beam, a pulse is sent onto a grating and the dispersed wavelengths are recombined in such a way that their interference are constructive only at the focal plane. While standard grating-TF requires high magnification, combining it with random speckle illumination (roughness-grating TF) enables micrometer-level optical sectioning at low magnification, suitable for large fields of view. We showed that combining roughness-grating TF with RIM improved both the transverse and axial resolutions of widefield 2PM.
\nFinally, we studied the interest of TF illumination for Coherent Anti-Stokes Raman Scattering (CARS) microscopy, a label-free technique for probing specific chemical bonds. We showed theoretically and experimentally that by temporally focusing both the pump and Stokes beams, we could obtain optically sectioned CARS images in a widefield configuration.<\/p>\n

 <\/p>\n

Keywords :<\/strong> Non-linear microscopy, Super-resolution, Temporal focusing, Two-photon microscopy, Optical sectioning, Coherent anti-Stokes Raman scattering microscopy<\/p>\n

 <\/p>\n

 <\/p>\n","protected":false},"featured_media":1319,"template":"","type-animation":[50],"class_list":{"0":"post-5165","1":"animation","2":"type-animation","3":"status-publish","4":"has-post-thumbnail","6":"entry"},"acf":[],"lang":"en","translations":{"en":5165,"fr":5166},"pll_sync_post":[],"_links":{"self":[{"href":"https:\/\/www.fresnel.fr\/wp\/wp-json\/wp\/v2\/animation\/5165","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.fresnel.fr\/wp\/wp-json\/wp\/v2\/animation"}],"about":[{"href":"https:\/\/www.fresnel.fr\/wp\/wp-json\/wp\/v2\/types\/animation"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.fresnel.fr\/wp\/wp-json\/wp\/v2\/media\/1319"}],"wp:attachment":[{"href":"https:\/\/www.fresnel.fr\/wp\/wp-json\/wp\/v2\/media?parent=5165"}],"wp:term":[{"taxonomy":"type-animation","embeddable":true,"href":"https:\/\/www.fresnel.fr\/wp\/wp-json\/wp\/v2\/type-animation?post=5165"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}