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Register a new userHigh speed determination of laser wavelength using Poincare descriptors of speckle
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Laser speckle can provide a powerful tool that may be used for metrology, for example measurements of the incident laser wavelength with a resolution beyond that which may be achieved in a commercial device. However, to realise highest resolution requires advanced multi-variate analysis techniques, which limit the acquisition rate of such a wavemeter. Here we show an arithmetically simple method to measure wavelength changes with dynamic speckle, based on a Poincar`e descriptor of the speckle pattern. We demonstrate the measurement of wavelength changes at femtometer-level with a measurement time reduced by two orders of magnitude compared to the previous state-of-the-art, which offers promise for applications such as speckle-based laser wavelength stabilisation.
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Many areas of optical science require an accurate measurement of optical spectra. Devices based on laser speckle promise compact wavelength measurement, with attometer-level sensitivity demonstrated for single wavelength laser fields. The measurement of multimode spectra using this approach would be attractive, yet this is currently limited to picometer resolution. Here, we present a method to improve the resolution and precision of speckle-based multi-wavelength measurements. We measure multiple wavelengths simultaneously, in a device comprising a single 1 m-long step-index multimode fiber and a fast camera. Independent wavelengths separated by as little as 1 fm are retrieved with 0.2 fm precision using Principal Component Analysis. The method offers a viable way to measure sparse spectra containing multiple individual lines and is likely to find application in the tracking of multiple lasers in fields such as portable quantum technologies and optical telecommunications.
We have developed a coherent Raman imaging platform using broadband coherent anti-Stokes Raman scattering (BCARS) that provides an unprecedented combination of speed, sensitivity, and spectral breadth. The system utilizes a unique configuration of laser sources that probes the Raman spectrum over 3,000 cm$^{-1}$ and generates an especially strong response in the typically weak Raman fingerprint region through heterodyne amplification of the anti-Stokes photons with a large nonresonant background (NRB) while maintaining high spectral resolution of $<$ 13 cm$^{-1}$. For histology and pathology, this system shows promise in highlighting major tissue components in a non-destructive, label-free manner. We demonstrate high-speed chemical imaging in two- and three-dimensional views of healthy murine liver and pancreas tissues and interfaces between xenograft brain tumors and the surrounding healthy brain matter.
Optical coherence tomography (OCT) is a powerful biomedical imaging technology that relies on the coherent detection of backscattered light to image tissue morphology in vivo. As a consequence, OCT is susceptible to coherent noise (speckle noise), which imposes significant limitations on its diagnostic capabilities. Here we show a method based purely on light manipulation that is able to entirely remove the speckle noise originating from turbid samples without any compromise in resolution. We refer to this method as Speckle-Free OCT (SFOCT). Using SFOCT, we succeeded in revealing small structures that are otherwise hidden by speckle noise when using conventional OCT, including the inner stromal structure of a live mouse cornea, the fine structures inside the mouse pinna, sweat ducts, and Meissners corpuscle in the human fingertip skin. SFOCT has the potential to markedly increase OCTs diagnostic capabilities of various human diseases by revealing minute features that correlate with early pathology.
Laser speckle is generated by the multiple interference of light through a disordered medium. Here we study the premise that the speckle pattern retains information about the polarisation state of the incident field. We analytically verify that a linear relation exists between the Stokes vector of the light and the resulting speckle pattern. As a result, the polarisation state of a beam can be measured from the speckle pattern using a transmission matrix approach. We perform a quantitative analysis of the accuracy of the transmission matrix method to measure randomly time-varying polarisation states. In experiment, we find that the Stokes parameters of light from a diode laser can be retrieved with an uncertainty of 0.05 using speckle images of 150$times$150 pixels and 17 training states. We show both analytically and in experiment that this approach may be extended to the case of more than one laser field, demonstrating the measurement of the Stokes parameters of two laser beams simultaneously from a single speckle pattern and achieving the same uncertainty of 0.05.
We present a new flexible high speed laser scanning confocal microscope and its extension by an astigmatism particle tracking device (APTV). Many standard confocal microscopes use either a single laser beam to scan the sample at relatively low overall frame rate, or many laser beam to simultaneously scan the sample and achieve a high overall frame rate. Single-laser-beam confocal microscope often use a point detector to acquire the image. To achieve high overall frame rates, we use, next to the standard 2D probe scanning unit, a second 2D scan unit projecting the image directly on a 2D CCD-sensor (re-scan configuration). Using only a single laser beam eliminates cross-talk and leads to an imaging quality that is independent of the frame rate with a lateral resolution of 0.235unit{mu m}. The design described here is suitable for high frame rate, i.e., for frame rates well above video rate (full frame) up to a line rate of 32kHz. The dwell time of the laser focus on any spot in the sample (122ns) is significantly shorter than in standard confocal microscopes (in the order of milli or microseconds). This short dwell time reduces phototoxicity and bleaching of fluorescent molecules. The new design opens further flexibility and facilitates coupling to other optical methods. The setup can easily be extended by an APTV device to measure three dimensional dynamics while being able to show high resolution confocal structures. Thus one can use the high resolution confocal information synchronized with an APTV dataset.
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