Confocal LiDAR for remote high-resolution imaging of auto-fluorescence in aquatic media.

Spatially resolved in situ monitoring of plankton can provide insights on the impacts of climate change on aquatic ecosystems due to their vital role in the biological carbon pump. However, high-resolution underwater imaging is technically complex and restricted to small close-range volumes with current techniques. Here, we report a novel inelastic scanning confocal light detection and ranging (LiDAR) system for remote underwater volumetric imaging of fluorescent objects.

CW coherent detection lidar for micro-Doppler sensing and raster-scan imaging of drones.

We demonstrate a continuous-wave (CW) coherent detection lidar (CDL) capable of detecting micro-Doppler (propeller) signatures and acquiring raster-scan images of small unmanned aerial systems/vehicles (UAS/UAV). The system uses a narrow-linewidth 1550 nm CW laser and takes advantage of mature and low-cost fiber-optics components from the telecommunications industry. Using either collimated or focused probe beam geometry, lidar based detection of characteristic periodic motions of drone propellers up to a remote distance of 500 m has been achieved.

High-resolution mid-infrared optical coherence tomography with kHz line rate.

We report on mid-infrared optical coherence tomography (OCT) at 4 µm based on collinear sum-frequency upconversion and promote the A-scan scan rate to 3 kHz. We demonstrate the increased imaging speed for two spectral realizations, one providing an axial resolution of 8.6 µm, and one providing a record axial resolution of 5.

Upconversion dark-field imaging with extended field of view at video frame rate.

Dark-field imaging is a well-known optical method for obtaining edge-enhanced images of objects containing steep gradients in either amplitude or phase. Edge enhancement is commonly achieved by using a small physical obstruction in the center of the Fourier plane of a 4f imaging setup. By blocking the low spatial frequencies in the center of the Fourier plane, only the higher spatial frequencies from the object reach the image plane.

Nonlinear optical vortex coronagraph.

A nonlinear optical vortex coronagraph (n-OVC) based on sum-frequency generation (SFG) in a periodically poled lithium niobate (PPLN) crystal is presented. We demonstrate an n-OVC by mixing the image of an on-axis point source ($ {\lambda _s} = 1.6\;{\unicode{x00B5}{\rm m}} $λ=1.

Enhancing the detectivity of an upconversion single-photon detector by spatial filtering of upconverted parametric fluorescence.

Due to advantages of low dark-count rate, reduced dead-time, and room-temperature operation, single-photon upconversion detectors for the telecom band are gaining strong interest as an alternative to other single-photon counters. In this work, we investigate the spatial and spectral distribution of upconverted spontaneous parametric downconversion (USPDC) noise, which is the typical dominant noise source in short-wavelength-pumped single-photon upconversion detectors for 1.5 µm - 1.

Time-resolved infrared photoluminescence spectroscopy using parametric three-wave mixing with angle-tuned phase matching.

A setup for time-resolved photoluminescence spectroscopy, based on parametric three-wave mixing in a periodically poled lithium niobate crystal, is characterized. Special attention is given to adjusting the phase matching condition by angle tuning of the luminescent light relative to a strong, continuous-wave laser beam within the crystal. The detection system is capable of operating at room temperature and in a wavelength range from 1.

Upconversion detector for range-resolved DIAL measurement of atmospheric CH.

We demonstrate a robust, compact, portable and efficient upconversion detector (UCD) for a differential absorption lidar (DIAL) system designed for range-resolved methane (CH) atmospheric sensing. The UCD is built on an intracavity pump system that mixes a 1064 nm pump laser with the lidar backscatter signal at 1646 nm in a 25-mm long periodically poled lithium niobate crystal. The upconverted signal at 646 nm is detected by a photomultiplier tube (PMT).

GHz-bandwidth upconversion detector using a unidirectional ring cavity to reduce multilongitudinal mode pump effects.

We demonstrate efficient upconversion of modulated infrared (IR) signals over a wide bandwidth (up to frequencies in excess of 1 GHz) via cavity-enhanced sum-frequency generation (SFG) in a periodically poled LiNbO. Intensity modulated IR signal is produced by combining beams from two 1547 nm narrow-linewidth lasers in a fiber coupler while tuning their wavelength difference down to 10 pm or less. The SFG crystal is placed inside an Nd:YVO ring cavity that provides 1064 nm circulating pump powers of up to 150 W in unidirectional operation.

Upconversion imaging using short-wave infrared picosecond pulses.

To the best of our knowledge, we present the first demonstration of short-wavelength infrared image upconversion that employs intense picosecond signal and pump beams. We use a fiber laser that emits a signal beam at 1877 nm and a pump beam at 1550 nm-both with a pulse width of 1 ps and a pulse repetition rate of 21.7 MHz.

Eye-safe diode laser Doppler lidar with a MEMS beam-scanner.

We present a novel Doppler lidar that employs a cw diode laser operating at 1.5 μm and a micro-electro-mechanical-system scanning mirror (MEMS-SM). In this work, two functionalities of the lidar system are demonstrated.

Diode laser lidar wind velocity sensor using a liquid-crystal retarder for non-mechanical beam-steering.

We extend the functionality of a low-cost CW diode laser coherent lidar from radial wind speed (scalar) sensing to wind velocity (vector) measurements. Both speed and horizontal direction of the wind at ~80 m remote distance are derived from two successive radial speed estimates by alternately steering the lidar probe beam in two different lines-of-sight (LOS) with a 60° angular separation. Dual-LOS beam-steering is implemented optically with no moving parts by means of a controllable liquid-crystal retarder (LCR).

Remote wind sensing with a CW diode laser lidar beyond the coherence regime.

We experimentally demonstrate for the first time (to our knowledge) a coherent CW lidar system capable of wind speed measurement at a probing distance beyond the coherence regime of the light source. A side-by-side wind measurement was conducted on the field using two lidar systems with identical optical designs but different laser linewidths. While one system was operating within the coherence regime, the other was measuring at least 2.

Investigation of spherical aberration effects on coherent lidar performance.

In this paper we demonstrate experimentally the performance of a monostatic coherent lidar system under the influence of phase aberrations, especially the typically predominant spherical aberration (SA). The performance is evaluated by probing the spatial weighting function of the lidar system with different telescope configurations using a hard target. It is experimentally and numerically proven that the SA has a significant impact on lidar antenna efficiency and optimal beam truncation ratio.

Monostatic coaxial 1.5 μm laser Doppler velocimeter using a scanning Fabry-Perot interferometer.

We present a laser Doppler velocimeter (LDV) in monostatic coaxial arrangement consisting of off-the-shelf telecom-grade components: a single frequency laser (wavelength λ = 1.5 μm) and a high-finesse scanning Fabry-Perot interferometer (sFPI). In contrast to previous 1.

Field performance of an all-semiconductor laser coherent Doppler lidar.

We implement and test what, to our knowledge, is the first deployable coherent Doppler lidar (CDL) system based on a compact, inexpensive all-semiconductor laser (SL). To demonstrate the field performance of our SL-CDL remote sensor, we compare a 36 h time series of averaged radial wind speeds measured by our instrument at an 80 m distance to those simultaneously obtained from an industry-standard sonic anemometer (SA). An excellent degree of correlation (R2=0.

Reduction of phase-induced intensity noise in a fiber-based coherent Doppler lidar using polarization control.

Optimization of signal-to-noise ratio is an important aspect in the design of optical heterodyne detection systems such as a coherent Doppler lidar (CDL). In a CDL, optimal performance is achieved when the noise in the detector signal is dominated by local oscillator shot-noise. Most modern CDL systems are built using rugged and cost-efficient fiber optic components.

Optical microassembly platform for constructing reconfigurable microenvironments for biomedical studies.

Cellular development is highly influenced by the surrounding microenvironment. We propose user-reconfigurable microenvironments and bio-compatible scaffolds as an approach for understanding cellular development processes. We demonstrate a model platform for constructing versatile microenvironments by fabricating morphologically complex microstructures by two-photon polymerization (2PP) and then assembling these archetypal building blocks into various configurations using multiple, real-time configurable counterpropagating-beam (CB) traps.

Accurate quantitative phase imaging using generalized phase contrast.

The generalized phase contrast (GPC) method is explored for improving the accuracy in quantitative reconstruction of two-dimensional phase distribution from images of semi-transparent objects viewed with a common-path interferometer (CPI). We propose a novel optical scheme for highly accurate determination of the object-dependent complex synthetic reference wave (SRW) in a CPI. Using a simple 4f imaging optical setup, GPC provides an analytic model of the SRW profile that is shown here to increase phase measurement accuracy over the entire output aperture.

Laser projection using generalized phase contrast.

We demonstrate experimental laser projection of a gray-level photographic image with 74% light efficiency using the generalized phase contrast (GPC) method. In contrast with a previously proposed technique [Alonzo, New J. Phys.

Direction-sensitive subwavelength displacement measurements at diffraction-limited spatial resolution.

Direction-sensitive displacement measurements at diffraction-limited spatial resolution are demonstrated with an interferometric optical-feedback semiconductor laser confocal imaging system. Subwavelength axial movements of the reflecting sample, including the directions of motion, are detected within the depth of field. A comparison of theory and actual instrument performance is presented.

2D optical manipulation and assembly of shape-complementary planar microstructures.

Optical trapping and manipulation offer great flexibility as a non-contact microassembly tool. Its application to the assembly of microscale building blocks may open new doors for micromachine technology. In this work, we demonstrate all-optical assembly of microscopic puzzle pieces in a fluidic environment using programmable arrays of trapping beams.

Fully automated beam-alignment and single stroke guided manual alignment of counter-propagating multi-beam based optical micromanipulation systems.

In a previous paper [J. S. Dam et al, Opt.

Computerized "drag-and-drop" alignment of GPC-based optical micromanipulation system.

In the past, aligning the counterpropagating beams in our 3D real-time generalized phase contrast (GPC) trapping system has been a task requiring moderate skills and prior experience with optical instrumentation. A ray transfer matrix analysis and computer-controlled actuation of mirrors, objective, and sample stage has made this process user friendly. The alignment procedure can now be done in a very short time with just a few drag-and-drop tasks in the user-interface.

GPC-based optical micromanipulation in 3D real-time using a single spatial light modulator.

Using a novel dual-beam readout with the generalized phase contrast (GPC) method, a multiple-beam 3D real-time micromanipulation system requiring only one spatial light modulator (SLM) has been realized. A theoretical framework for the new GPC scheme with two parallel illumination beams is presented and corroborated with an experimental demonstration. Three-dimensional arrays of polystyrene microbeads were assembled in the newly described system.