No abstract

Femtosecond stimulated Raman microscopy (FSRM) aims at the reduction of acquisition times in Raman microscopy while preserving the spectral coverage. An improved light source for FSRM is briefly described. This light source delivers a narrow bandwidth Raman pump pulse and a broad‐band Raman probe. The small spectral changes (relative magnitude 10−6 to 10−3) in the probe light due to the stimulated Raman effect are recorded simultaneously relying on array detectors. Here, estimates for the parameters of an ideal detector are derived and compared with the technical status quo of available detectors. Copyright © 2014 John Wiley & Sons, Ltd.

Additive manufacturing (AM) is a production technology where material is accumulated to create a structure, often through added shaped layers. The major advantage of additive manufacturing is in creating unique and complex parts for use in areas where conventional manufacturing reaches its limitations. However, the current class of AM systems produce parts that contain structural defects (e.g., cracks and pores) which is not compatible with certification in high value industries. The probable complexity of an AM design increases the difficulty of using many non-destructive evaluation (NDE) techniques to inspect AM parts—however, a unique opportunity exists to interrogate a part during production using a rapid surface based technique. Spatially resolved acoustic spectroscopy (SRAS) is a laser ultrasound inspection technique used to image material microstructure of metals and alloys. SRAS generates and detects `controlled’ surface acoustic waves (SAWs) using lasers, which makes it a non-contact and non-destructive technique. The technique is also sensitive to surface and subsurface voids. Work until now has been on imaging the texture information of selective laser melted (SLM) parts once prepared (i.e., polished with R a < 0 . 1 μ m)—the challenge for performing laser ultrasonics in-process is measuring waves on the rough surfaces present on as-deposited parts. This paper presents the results of a prototype SRAS system, developed using the rough surface ultrasound detector known as speckle knife edge detector (SKED)—texture images using this setup of an as-deposited Ti64 SLM sample, with a surface roughness of S a ≈ 6 μ m, were obtained.

This paper presents a multichannel, time-resolved picosecond laser ultrasound system that uses a custom complementary metal-oxide-semiconductor linear array detector. This novel sensor allows parallel phase-sensitive detection of very low contrast modulated signals with performance in each channel comparable to that of a discrete photodiode and a lock-in amplifier. Application of the instrument is demonstrated by parallelizing spatial measurements to produce two-dimensional thickness maps on a layered sample, and spectroscopic parallelization is demonstrated by presenting the measured Brillouin oscillations from a gallium arsenide wafer. This paper demonstrates the significant advantages of our approach to pump probe systems, especially picosecond ultrasonics.

Spatial modulation microscopy is a technique originally developed for quantitative spectroscopy of individual nano-objects. Here, a parallel implementation of the spatial modulation microscopy technique is demonstrated based on a line detector capable of demodulation at kHz frequencies. The capabilities of the imaging system are shown using an array of plasmonic nanoantennas and dendritic cells incubated with gold nanoparticles. PACS numbers:With the increasing employment of nanomaterials in physical and biomedical science, sensitive methods capable of screening and characterizing these materials are needed. Currently there is a range of optical microscopy techniques capable of imaging individual nanoparticles [3]. For nonfluorescent particles, interactions take place through absorption and/or scattering. Detection of scattered intensity, generally known as darkfield microscopy, is the most widely used technique, combining background-free imaging with a high spectral selectivity for e.g. optical sensing [1,2]. The efficiency of light scattering is greatly reduced with decreasing particle size, proportional to the square of the particle volume, which can be overcome using more advanced interferometric detection schemes [3,4]. Also scattering-based techniques are not suitable for materials with an a small dielectric contrast, i.e. index-matched particles in solution.A fundamentally different method of detection relies on detection of absorption rather than scattering of light. The most sensitive of these techniques is photothermal imaging, where a thermal response caused by local absorption can be detected with single-molecule sensitivity [5]. Photothermal imaging methods require a relatively high laser intensity (MW/cm 2 ) over a diffraction limited spot, which limits the scalability of photothermal imaging in real-time and live cell applications. Spatial modulation microscopy (SMM) has been introduced as a technique for quantitative analysis of the optical extinction cross-section of small metal nanoparticles [6,7]. The method is based on recovery of a small modulation component in the transmitted (or reflected) light using lock-in detection. This spatial modulation is achieved by means of a periodical displacement of the specimen in a Gaussian laser focus. While the technique is less sensitive than photothermal imaging, it allows for precise in-situ quantitative spectroscopy of nanomaterials which can then be correlated to other properties such as their ultrafast response [8]. In addition, the SMM technique is scalable as it works at moderate optical intensities, i.e. a few W/cm 2 per pixel, and requires only a small focal width in one dimension. No reports have been made yet on the potential of SMM for real-time imaging in biological systems.Here, we demonstrate the integration of SMM into a viable imaging system covering an area of tens of micrometers at a rate of around one image per second. The fast scanning spatial modulation method, makes use of a recently developed CMOS camera technology combining multip...

Abstract:In this paper a method of taking widefield heterodyne interferograms using a prototype modulated light camera is described. This custom CMOS modulated light camera (MLC) uses analogue quadrature demodulation at each pixel to output the phase and amplitude of the modulated light as DC voltages. The heterodyne interference fringe patterns are generated using an acousto-optical frequency shifter (AOFS) in an arm of a Mach-Zehnder interferometer. Widefield images of fringe patterns acquired using the prototype MLC are presented. The phase can be measured to an accuracy of ±6.6 • . The added value of this method to acquire widefield images are discussed along with the advantages.

No abstract

No abstract