Laser printing | EPFL Graph Search

Laser printing is an electrostatic digital printing process. It produces high-quality text and graphics (and moderate-quality photographs) by repeatedly passing a laser beam back and forth over a negatively charged cylinder called a "drum" to define a differentially charged image. The drum then selectively collects electrically charged powdered ink (toner), and transfers the image to paper, which is then heated to permanently fuse the text, imagery, or both, to the paper. As with digital photocopiers, laser printers employ a xerographic printing process. Laser printing differs from traditional xerography as implemented in analog photocopiers in that in the latter, the image is formed by reflecting light off an existing document onto the exposed drum. Invented at Xerox PARC in the 1970s, laser printers were introduced for the office and then home markets in subsequent years by IBM, Canon, Xerox, Apple, Hewlett-Packard and many others. Over the decades, quality and speed have increase

Single cell isolation process with laser induced forward transfer

Ying Chen, Yu Deng, Philippe Renaud

Background A viable single cell is crucial for studies of single cell biology. In this paper, laser-induced forward transfer (LIFT) was used to isolate individual cell with a closed chamber designed to avoid contamination and maintain humidity. Hela cells were used to study the impact of laser pulse energy, laser spot size, sacrificed layer thickness and working distance. The size distribution, number and proliferation ratio of separated cells were statistically evaluated. Glycerol was used to increase the viscosity of the medium and alginate were introduced to soften the landing process. Results The role of laser pulse energy, the spot size and the thickness of titanium in energy absorption in LIFT process was theoretically analyzed with Lambert-Beer and a thermal conductive model. After comprehensive analysis, mechanical damage was found to be the dominant factor affecting the size and proliferation ratio of the isolated cells. An orthogonal experiment was conducted, and the optimal conditions were determined as: laser pulse energy, 9 μJ; spot size, 60 μm; thickness of titanium, 12 nm; working distance, 700 μm;, glycerol, 2% and alginate depth, greater than 1 μm. With these conditions, along with continuous incubation, a single cell could be transferred by the LIFT with one shot, with limited effect on cell size and viability. Conclusion LIFT conducted in a closed chamber under optimized condition is a promising method for reliably isolating single cells.

Biomed Central Ltd2017

Application of Adaptive Optics to Focusing and Imaging

Daniel Iwaniuk

Adaptive optics is used to abate aberrations with a wavefront correction. It is widely used in astronomy and is starting to expand into applications of laser focusing and imaging with high numerical apertures, e.g. microscopy. The physical background of focusing laser light and imaging is the same, so we can use the same methods. In both cases, light is propagating through a lens; either it becomes focused into a small region or light from a small region becomes imaged on a camera. Modulations applied on the lens to implement wavefront corrections behave similarly in both applications. A powerful simulation tool was created to characterize the impact of those modulations. As an example, we validated a design for a Fresnel lens produced on a glass fibre tip to focus its emitting light. We have developed solutions mainly for three different problems. First, a high depth of focus enables keeping a laser beam focused within a larger length or imaging objects from different positions simultaneously. In photography, this can be attained by stopping down the aperture, which introduces a huge loss of light. State-of-the-art for focusing into a line segment also shows an inefficient performance. We present an elegant lens design, which enables highly efficient elongation of the depth of focus. Preliminary studies have shown that it might be a feasible alternative for current intra-ocular lens implants in ophthalmology or for 3D visualization in imaging and microscopy. A high depth of focus also has a large potential in optical lithography and data storage, because the focal position is enlarged and does not have to be adjusted precisely to obtain a useful spot. Second, specimen-induced aberrations can affect even a perfectly adjusted, diffraction limited lens system. A planar refraction index mismatch introduces spherical aberrations, degrading the optical resolution. As a first step to correct them, we were able to characterize simultaneously the refractive index and the thickness of an unknown medium that is placed between the lens and its focal region. This was done by clever manipulation of the beam angles with the same adaptive optics element in the focusing and in the imaging system. Finally, the medium-induced spherical aberrations were corrected based on the characterization results. The point spread function degradation of a focused laser beam was completely removed, which might be useful in optical tweezers or in laser processing of biological samples. While imaging through the planar refractive index mismatch, the bending of the object field was corrected and the diffraction limited performance restored.

EPFL2012

Highly sensitive SnO2 sensor via reactive laser-induced transfer

Alain Grisel, Ulrike Lehmann, Alexander Wokaun

Gas sensors based on tin oxide (SnO2) and palladium doped SnO2 (Pd:SnO2) active materials are fabricated by a laser printing method, i.e. reactive laser-induced forward transfer (rLIFT). Thin films from tin based metal-complex precursors are prepared by spin coating and then laser transferred with high resolution onto sensor structures. The devices fabricated by rLIFT exhibit low ppm sensitivity towards ethanol and methane as well as good stability with respect to air, moisture, and time. Promising results are obtained by applying rLIFT to transfer metal-complex precursors onto uncoated commercial gas sensors. We could show that rLIFT onto commercial sensors is possible if the sensor structures are reinforced prior to printing. The rLIFT fabricated sensors show up to 4 times higher sensitivities then the commercial sensors (with inkjet printed SnO2). In addition, the selectivity towards CH4 of the Pd:SnO2 sensors is significantly enhanced compared to the pure SnO2 sensors. Our results indicate that the reactive laser transfer technique applied here represents an important technical step for the realization of improved gas detection systems with wide-ranging applications in environmental and health monitoring control.

Nature Publishing Group2016

Application of Adaptive Optics to Focusing and Imaging

Daniel Iwaniuk

EPFL2012