We present an effective method to extend the mode-hop-free (MHF) tuning range of an external-cavity diode laser (ECDL) by synchronous tuning of the longitudinal modes of the external cavity and the internal cavity, with the mode also matched in the initial state. Both the principle of synchronous tuning and the condition of mode matching in a Littman-configuration ECDL are introduced. The necessary tuning parameters could simply be estimated by the output power curve of the tuning with a single photodiode. By using this tuning method, we increased the MHF tuning range of an ECDL with a nonoptimized reflector pivot position from several gigahertzes to over 78 GHz around 774.5 nm. The tuning performance of the ECDL could meet the requirement of frequency scanned interferometry.

We have shown that the maximum achievable resolution of an in-line lensless holographic microscope is limited by aliasing and, for collimated illumination, cannot exceed the camera pixel size. This limit can be achieved only when the optimal conditions on the spatial and temporal coherence state of the illumination are satisfied. The expressions defining the configuration, delivering maximum resolution with given spatial and temporal coherence of the illumination, are obtained. The validity of these conditions is confirmed experimentally.

In this Letter, we show that a Shack–Hartmann wavefront sensor can be used for the quantitative measurement of the specimen optical path difference (OPD) in an ordinary incoherent optical microscope, if the spatial coherence of the illumination light in the plane of the specimen is larger than the microscope resolution. To satisfy this condition, the illumination numerical aperture should be smaller than the numerical aperture of the imaging lens. This principle has been successfully applied to build a high-resolution reference-free instrument for the characterization of the OPD of micro-optical components and microscopic biological samples.

We present a structured illumination microscopy system that projects a hexagonal pattern by the interference among three coherent beams, suitable for implementation in a light-sheet geometry. Seven images acquired as the illumination pattern is shifted laterally can be processed to produce a super-resolved image that surpasses the diffraction-limited resolution by a factor of over 2 in an exemplar light-sheet arrangement. Three methods of processing data are discussed depending on whether the raw images are available in groups of seven, individually in a stream or as a larger batch representing a three-dimensional stack. We show that imaging axially moving samples can introduce artefacts, visible as fine structures in the processed images. However, these artefacts are easily removed by a filtering operation carried out as part of the batch processing algorithm for three-dimensional stacks. The reconstruction algorithms implemented in Python include specific optimizations for calculation on a graphics processing unit and we demonstrate its operation on experimental data of static objects and on simulated data of moving objects. We show that the software can process over 239 input raw frames per second at 512 × 512 pixels, generating over 34 super-resolved frames per second at 1024 × 1024 pixels. This article is part of the Theo Murphy meeting issue ‘Super-resolution structured illumination microscopy (part 1)’.

Mode hopping is a critical performance limitation of external cavity diode lasers (ECDLs). We developed a method to suppress the mode hops by shifting the internal cavity longitudinal mode spectrum to match the other mode spectra. A model of longitudinal mode structure based on Littman–Metcalf configuration has been deduced for analyzing the characteristics of external cavity mode hop and internal cavity mode hop. The best mode matching point appears at the peak of output power when tuning the ECDL. Both the short-term and long-term wavelength stability were investigated in different laser diode current values while the tuning element maintains a fixed position. The experimental results demonstrated the effectiveness of the proposed mode matching methods for improving the mode stability and reducing the sensitivity to environment change.

Structured Illumination Microscopy (SIM) is a key technology for high resolution and super-resolution imaging of biological cells and molecules. The spread of portable and easy-to-align SIM systems requires the development of novel methods to generate a light pattern and to shift it across the field of view of the microscope. Here we show a miniaturized chip that incorporates optical waveguides, splitters, and phase shifters, to generate a 2D structured illumination pattern suitable for SIM microscopy. The chip creates three point-sources, coherent and controlled in phase, without the need for further alignment. Placed in the pupil of a microscope’s objective, the three sources generate a hexagonal illumination pattern on the sample, which is spatially translated thanks to thermal phase shifters. We validate and use the chip, upgrading a commercial inverted fluorescence microscope to a SIM setup and we image biological sample slides, extending the resolution of the microscope.