In this work, we present experimental results on the optical trapping and manipulation of micro- and nanoparticles using plasmonic tweezers based on arrays of annular nanoapertures. By increasing the inner disk size of the nanoaperture, a redshift of the resonant wavelength is observed. We demonstrate both trapping and transportation of particles across the plasmonic device using a drag force method with incident laser intensities less than 1.5 mWμm<sup>−2</sup>. We calculate trap stiffnesses equal to 0.25 pN/μm·mW and 1.07 pN μm<sup>−1</sup>mW<sup>−1</sup> for 0.5 μm and 1 μm diameter particles, respectively. A high trap stiffness of 0.85 fN/nm· mW at a low incident laser intensity of ~0.51 mW/μm<sup>2</sup> at 980 nm was obtained for 30 nm diameter polystyrene particles. We perform sequential single-nanoparticle trapping within specific trapping sites. The demonstrated plasmonic nanotweezers could be used for lab-on-a-chip devices where efficient particle trapping with high tunability of the applied laser wavelength is required.
Microfluidic devices provide a platform with wide ranging applications from environmental monitoring to disease diagnosis. They offer substantive advantages but are often not optimized or designed to be used by nonexpert researchers. Microchannels of a microanalysis platform and their geometrical characterization are of eminent importance when designing such devices. We present a method that is used to optimize each microchannel within a device using high-throughput particle manipulation. For this purpose, glass-based microfluidic devices, with three-dimensional channel networks of several geometrical sizes, were fabricated by employing laser fabrication techniques. The effect of channel geometry was investigated by employing an optical tweezer. The optical trapping force depends on the flow velocity that is associated with the dimensions of the microchannel. We observe a linear dependence of the trapping efficiency and of the fluid flow velocity, with the channel dimensions. We determined that the highest trapping efficiency was achieved for microchannels with aspect ratio equal to one. Numerical simulation validated the impact of the device design dimensions on the trapping efficiency. This investigation indicates that the geometrical characteristics, the flow velocity, and trapping efficiency are crucial and should be considered when fabricating microfluidic devices for cell studies.
As one of the major health problems for mankind is cancer, any development for the early detection and effective treatment of cancer is crucial to saving lives. Worldwide, the dream for the anti-cancer procedure of attack is the development of a safe and efficient early diagnosis technique, the so called “optical biopsy”. As early diagnosis of cancer is associated with improved prognosis, several laser based optical diagnostic methods were developed to enable earlier, non-invasive detection of human cancer, as Laser Induced Fluorescence spectroscopy (LIFs), Diffuse Reflectance spectroscopy (DRs), confocal microscopy, and Optical Coherence Tomography (OCT). Among them, Optical Coherence Tomography (OCT) imaging is considered to be a useful tool to differentiate healthy from malignant (e.g. basal cell carcinoma, squamous cell carcinoma) skin tissue. If the demand is to perform imaging in sub-tissular or even sub-cellular level, optical tweezers and atomic force microscopy have enabled the visualization of molecular events underlying cellular processes in live cells, as well as the manipulation and characterization of microscale or even nanoscale biostructures. In this work, we will present the latest advances in the field of laser imaging and manipulation techniques, discussing some representative experimental data focusing on the 21th century biophotonics roadmap of novel diagnostic and therapeutical approaches. As an example of a recently discussed health and environmental problem, we studied both experimentally and theoretically the optical trapping forces exerted on yeast cells and modified with estrogen-like acting compounds yeast cells, suspended in various buffer media.
In recent years, lasers for optical trapping and micromanipulation of microscopic particles or cells and sub cellular
structures, both in vivo and in vitro, have gained remarkable interest in biomedical research and applications. Although
the principles and the mechanisms of pulsed laser ablation have been well described for macroscopic interventions, the
microbeam operation under microscopic guidance necessitates further investigation. In this work, we present the research
and development efforts towards a pulsed ultraviolet microbeam laser system, the design and realization efforts towards
a near infrared laser trapping device and the results obtained on yeast cells and algae by the combined system. We
investigated the optical dissection of the cells versus the presence of optical trapping forces and the presence of
rhodamine dye. We characterized the optical ablation of the cell walls and resulting cavitation as plasma formation
effects which create shock waves due to their occurrence only in nanosecond pulse irradiation mode. We estimated the
minimum energy of the microbeam for optical dissection of yeast cell, under the influence of optical trapping forces, as
lower as 3 μJ, while in the presence of rhodamine as lower as 2 μJ. Lastly, using the techniques of optical microsurgery
we demonstrated the minimum energy value for sub cellular dissection on an algae cell equal to 27 μJ.
Optical tweezers is a powerful tool which is used to capture and manipulate microscopic particles such as dielectric
microspheres and cells. In the single optical trap the beam is strongly focused to a diffraction limited spot by a high
numerical aperture objective. Resently a new version of optical trap was demonstrated with optical fibers. Compared
with the common optical tweezers which required high power microscope objective and carefully adjusted optical path,
the fiber optical tweezers are compact in size and less expensive. Moreover, they have also a working distance not
necessarily close to the objective as for a typical optical tweezers.
In this work we present the development of a single beam optical fiber trapping system integrated with an optical fiber
ablation system for micromanipulation of biological objects. The fiber trap was formed using a continuous wave He-Ne
laser operating at 632.8 nm. The fiber ablation system was formed using a free-running Er:YAG laser operating at 2.94
μm with pulse duration of 80 μm. The ablation beam was coupled into the front end of a fluoride glass optical fiber via a
focusing lens of 100 mm and a pinhole of 50 μm. We evaluated the fluoride glass optical fiber as far as attenuation and
as far as the spatial distribution of the energy output is concerned. We verified that optical trapping and the
micromanipulation of micro objects were easily achieved, by a focused laser beam, emerging from optical fiber inclined
at 42 degrees to the sample.
A considerable interest, in the recent years, has been allocated in the mid-infrared Er:YAG laser surgery and
microsurgery. This interest has been increased after the development of optical fibers and waveguides, for safe and
efficient transmission of the ~3.0 μm wavelength beams. On the other hand, a laser delivery system based on
common silica glass fibers and caps are not applicable for delivery of the Er:YAG laser light, due to high absorption
losses at the mid-infrared wavelengths. Thus, fluoride glass fibers and sealing quartz caps is a promising
combination for laser delivery due to their low transmission loss. In this study, we investigated the properties of
three sealing quartz caps, suitable for fluoride glass optical fibers, with various distal end geometries, in order to
evaluate the attenuation and the spatial and temporal energy distribution of the transmitted laser radiation. Moreover,
we evaluated the experimental beam divergence of the sealing caps. As a transmission medium, three fluoride glass
optical fibers were used. As a laser source we used a Q-switched Er:YAG laser with a pulse duration of 190 ns and a
repetition rate of 1 Hz. The mean value of the energy loss for dome geometry was found (0.73 ± 0.03), for planoconvex
geometry was found (0.76 ± 0.03) and for ball geometry was found (0.73 ± 0.05). The beam divergence was
found (62.4 ± 0.1) mrad, (156.2 ± 0.3) mrad and (37.5 ± 0.5) mrad for dome, ball and plano-convex geometry,
Lasers can provide a precious tool to conservation process due to their accuracy and the controlled energy they
deliver, especially to fragile organic material such as paper. The current study concerns laser modification such as paper
cleaning, initially of test papers artificially soiled and then of an original book of the early 20<sup>th</sup> Century. The test objects
were A4 copier paper, newspaper, and paper Whatman No.1056. During the experiments, ink of a pen, pencil and ink
from a stamp was mechanically employed on each paper surface. Laser cleaning was applied using a Q-switched
Nd:YAG operating at 532 nm and CO<sub>2</sub> laser at 10.6 μm for various fluences. The experimental results were presented by
using optical microscopy. Eventually, laser cleaning of ink was performed to a book of 1934, by choosing the best
conditions and parameters from cleaning the test samples, like Nd:YAG laser operating at 532 nm.
Laser optical trapping and micromanipulation of microparticles or cells and subcellular structures have gained remarkable interest in biomedical research and applications. Several laser sources are employed for the combination of a laser scalpel with an optical tweezers device, under microscopic control. However, although the principles and the mechanisms of pulsed laser ablation have been well described for macroscopic interventions, the microbeam operation, under microscopic guidance, necessitates further experiments and investigations.
We present experimental results of controlled micro-ablation of PMMA beads of 3-8 μm diameters, trapped by laser tweezers in various media e.g. solutes of different index of refraction. An optical tweezers system, based on a continuous wave He-Ne laser emitting at 632.8 nm, was tested on beads and, despite the low power of the He-Ne laser, the optical trap was stable. Another optical system, based on a cw Nd:YAG laser emitting at 1.06 μm, was tested on microspheres too. Successful beads ablation was carried out by irradiation with multiple, or even a single nitrogen laser pulse of 7 ns pulse duration at a wavelength of 337 nm. The ablative perforation of the microspheres was estimated by controlling the laser fluence. Moreover, shape deformations of PMMA microspheres were observed. The experimentally obtained results are theoretically explained via the spatial intensity distribution based on Mie light scattering theory. Furthermore, the appearance of laser ablation holes in the back side of microspheres is explained by the ablation triggered shock waves propagation. The role of the stretching forces action is also discussed. Additionally, we report experimental results on measuring the optical trap force of PMMA beads. A powerful optical tweezers system based on a continuous wave Nd:YAG laser was used in order to estimate the trapping efficiency for several beads diameter.
The photon drag effect has been observed in several semiconductors. It arises from the transfer of momentum from
laser radiation to mobile electrons or holes in the material. The sign and the magnitude of the effect depend on the
combination of optical, transport and band structure properties of the semiconductor as well as the magnitude of the
radiation momentum. The optical rectification is a second order phenomenon arising from the generation of polarization
in a non-linear medium at the passage of an intense optical beam. Both effects are generally referred as radiation pressure
effects. The intention of this work is to present and discuss new experimental evidence of photon drag-effect in diamond
structure and photon drag-optical rectification in III-V semiconductors using Er:YAG laser emitting at 2.94 μm, CO<sub>2</sub>
laser emitting at 10.6 μm and at 9.6 μm, Nd:YAG laser emitting at 1.06 μm, Er:Tm:Ho:YLF laser emitting at 2.06 μm
and Cr:Tm:Ho:YAG laser emitting at 2.08 μm. No saturation effects were found indicating that detectors based on these
effects can be used as recording devices of pulses down to 0.1 ns. Measurements have been made on the response of the
photon drag and the optical rectification detectors of Ge, Si, GaAs, GaP of several orientations. The responsivity results
are converted, using the relevant theoretical equations, in to S, P and D coefficients. The experimentally obtained results
are theoretically explained and are compared with previous results of other wavelengths in the literature.
In recent years, lasers for optical trapping and micromanipulation of microscopic particles or cells and subcellular
structures, both in vivo and in vitro, have gained remarkable interest in biomedical research and applications. On the
other hand, a highly focused pulsed laser allows ablation and microdissection of biological material with high spatial
resolution. In 1989 the microbeam field and the optical trapping field were merged by the first combination of laser
microbeams and optical tweezers. Several laser sources are employed for the combination of a laser scalpel with an
optical trapping device, under microscopic control. For example a pulsed laser microbeam that emits in the ultraviolet or
the visible range of the electromagnetic spectrum can be used to form submicrometer cuts in biological material or to
ablate parts specific cells. However, although the principles and the mechanisms of pulsed laser ablation have been well
described for macroscopic interventions, the microbeam operation under microscopic guidance necessitates further
investigation. In this work, we present the research and development efforts towards a pulsed UV microbeam laser
system, the design and realization efforts towards a visible laser trapping system and the first results obtained on yeast
cells by the combined system. The nitrogen laser microbeam setup, with special UV mirrors, lenses and a microscope in
which ablation and the He-Ne optical tweezers are combined, performs the microsurgery and micromanipulation. This
Uv laser based setup provides good spatial resolution for microdissection. The beam quality delivered by the laser is of
great importance in microscopy controlled ablating operations and therefore was extensively studied.