Nonredundant Raman imaging using optical eigenmodes

Abstract

Various forms of imaging schemes have emerged over the last decade that are based on correlating variations in incident illuminating light fields to the outputs of single 'bucket' detectors. However, to date, the role of the orthogonality of the illumination fields has largely been overlooked and furthermore, the field has not progressed beyond bright field imaging. By exploiting the concept of orthogonal illuminating fields, we demonstrate the application of optical eigenmodes (OEi) to wide field, scan-free spontaneous Raman imaging, which is notoriously slow in wide-field mode. The OEi approach enables a form of indirect imaging that exploits both phase and amplitude in image reconstruction. The use of orthogonality enables us to non-redundantly illuminate the sample and, in particular, use a subset of illuminating modes to obtain the majority of information from the sample, thus minimising any photobleaching or damage of the sample. The crucial incorporation of phase, in addition to amplitude, in the imaging process significantly reduces background noise and results in an improved SNR for the image while reducing the number of illuminations. As an example we can reconstruct images of a surface-enhanced Raman spectroscopy (SERS) active sample with approximately an order of magnitude fewer acquisitions. This generic approach may readily be applied to other imaging modalities such as fluorescence microscopy or nonlinear vibrational microscopy.

Discrimination and classification of acute lymphoblastic leukemia cells by Raman spectroscopy

“…Advanced photonic techniques may play a pivotal role in early leukemia detection and classification because they are non-invasive, offer single molecule detection sensitivity [5,6], and allow functional imaging at micro-or even nano-scale resolution [6][7][8][9]. In terms of a label-free method, RS is more attractive than fluorescence because it provides specific biochemical cellular information and does not require any labeling [10][11][12][13][14][15].…”

Spermatozoa quality assessment: a combined holographic and Raman microscopy approach

“…In particular, we are implementing around the same optical microscope a novel combined system allowing the simultaneous holographic and biochemical characterization of the sample 26 . Alternative experimental configurations, such as the implementation in microfluidic environments 27 , the adoption of compressive methods 22,33 and improving data analysis 28 , are required in order to improve the DH-RS approach throughput, in terms of automation, higher analyzed cell number and sensitivity/specificity.…”

“…When the morphological analysis needs to be integrated with biochemical information, RS can be efficiently used. Indeed, RS is a sensitive and non-invasive method with resolution in the sub-micrometer range that allows the chemical assessment of single cells by detecting their biomolecule vibrations, serving as a cellular intrinsic 'fingerprint' 3,[15][16][17][18][19][20][21][22][23][24][25][26] . It can be also used to provide pseudo-color images according to the Raman spectral band intensities allowing the identification of cell phenotype and physiological state [23][24][25][26][27][28][29][30][31][32] .…”

Nonlinear optical eigenmodes: perturbative approach

“…Due to the interaction terms in Eqs. (5) to conserve the vortex charge during propagating we have the selection rule, l b = l 3 − l 2 . This is illustrated in the eigenmodes shown in Fig.…”