mW Laser Power Research Articles

Simultaneous detection of ammonia, methane and ethylene at 1.63 μm with diode laser photoacoustic spectroscopy

Spectral investigation around 6115 cm-1 for simultaneous detection of ammonia, methane and ethylene in gas samples is presented. Experimental data on the ν2+ν3+ν4 combination band of ammonia are reported with a resolution of 1.5 GHz. A trace gas analyzer based on a resonant photoacoustic cell and an external cavity diode laser has been used for detection. A data fitting procedure has been developed in order to improve the system sensitivity and to limit the need of a reference cell. The selected spectral region allows a sensitivity of about 60 ppm for ammonia, 6 ppm for methane and 30 ppm for ethylene with 0.3 mW laser power. An application of simultaneous detection of such molecules in a mixture reproducing their typical abundances in real gas samples from biomass gasification is discussed.

Photochemical Kinetics of Maleic to Fumaric Acid on Silver Nanoparticle Surfaces

A visible photochemistry of maleic to fumaric acid adsorbed on silver nanoparticle surfaces was investigated as probed by SERS using a simple flow method. Photoisomerization of maleic to fumaric acid was consecutively observed in the condition of various flow rates, which varied the exposure time of laser beam. The sequential SERS spectra of maleic acid indicated that the photochemical isomerization and desorption took place simultaneously on silver nanoparticle surfaces as a function of laser fluency and wavelength. For 530.9nm laser line excitation, the rate constant coefficients were obtained with a = 5.9 <TEX>$sec^{-1}$</TEX> mW for isomerization and b = 13.9 <TEX>$sec^{-1}$</TEX> mW for desorption, which <TEX>$k_1\;=\;aI^n\;and\;k_2\;=\;bI^m$</TEX>. Both reactions were one photon process (n = 1, m = 1) of a visible light and relatively fast process whose decay time was in the range of milli-second for 50 mW laser power. The rate of photochemical reaction increased on going toward the blue and photodesorption was a dominant process. A simple flow method used in this study was very useful to study a relatively fast photochemical reaction of molecules adsorbed on silver nanoparticle surfaces.

A316 液中固体微粒子のレーザマニピュレーション

By a scanning YAG laser beam, induced motions of solid fine particles for drawing alphabets and forced rotations of a non-sphere solid particle in water are discussed in this paper. By scanning the laser beam in high frequency, the beam is seemed as multi laser beams and plural objectives can be simultaneously manipulated by the beam. By these techniques arbitrary patterns of solid particles can be drawn. By the optical canning method of the galvano scanner with the Q-switch the rotational rates of the fragment with arbitrary shapes are from 0.5 Hz to 1.5 Hz at the 591 mW laser power. The rates are dependent on the scanning frequency.

Formaldehyde sensor using interband cascade laser based quartz-enhanced photoacoustic spectroscopy

A novel continuous-wave mid-infrared distributed feedback interband cascade laser was utilized to detect and quantify formaldehyde (H2CO) using quartz-enhanced photoacoustic spectroscopy. The laser was operated at liquid-nitrogen temperatures and provided single-mode output powers of up to 12 mW at 3.53 μm (2832.5 cm-1). The noise equivalent (1σ) detection sensitivity of the sensor was measured to be 2.2×10-8 cm-1 W (Hz)-1/2 for H2CO in ambient air, which corresponds to a detection limit of 0.6 parts in 106 by volume (ppmv) for a 10 s sensor time constant and 3.4 mW laser power delivered to the sensor module.

Transscleral thermotherapy with laser-induced and conductive heating in hamster Greene melanoma.

The purpose of this study was to investigate the cytotoxic effect of heat as induced by transscleral thermotherapy (TSTT), which may be of interest in the treatment of patients with choroidal melanoma. The aim of TSTT is to heat both the sclera and the tumor up to a cytotoxic temperature of about 60 degrees C. TSTT was performed in hamsters with subcutaneously implanted Greene melanoma covered by a specimen of human donor sclera of thickness 0.5, 0.7 or 0.9 mm. A newly developed applicator, which combines conductive episcleral heating at 60 degrees C with laser-induced heating, was used at laser powers ranging from 500 to 1500 mW delivered by an 810 nm diode laser, beam diameter 3 mm, and exposure time 1 min. Temperatures were measured at the scleral surface and at the sclera-tumor interface. The extent of tumor necrosis was examined by light microscopy and the sclera was examined by polarized light microscopy. Maximal depth of tumor necrosis without scleral damage was 4.4 (SD 1.5) mm. The temperature at the scleral surface after TSTT was 58.8 (SD 2.4) degrees C. The temperature at the sclera-tumor interface ranged from 56.4 (SD 3.7) degrees C at 500 mW to 65.3 (SD 4.4) degrees C at 1250 mW laser power. Structural changes to the scleral collagen started to develop at 1250 mW. TSTT with combined laser-induced and conductive heating caused cytotoxic temperatures in the tumor and the sclera, which were well tolerated by the scleral collagen.

An analytical system based on a compact flow cytometer for DNA fragment sizing and single-molecule detection.

Previous reports have demonstrated accurate DNA fragment sizing of linear DNA fragments, from 564 to approximately 4 x 10(5) bp, in a flow system. B-phycoerythrin (B-PE), commonly used in conventional cytometric applications that require high-sensitivity, was the first fluorophore detected in flow at the single-molecule level. Dilute solutions of stained DNA fragments or B-PE were analyzed in a simplified, compact flow system, with enhanced performance and lower cost, utilizing a solid-state laser and a single-photon sensing avalanche photodiode detector (SSAPD). Extensive data processing and display software, developed specifically for the photon-counting data stream, extracts correlated height, width, and area features from bursts of photons due to discrete molecules passing through the sensing region in the flow channel. DNA fragment sizing in flow has now been demonstrated for SYTOX-orange-stained fragments ranging in size over 3.4 orders of magnitude, from 125 to 5 x 10(5) bp. For Lambda bacteriophage DNA (lambda DNA; 48.5 kbp) a CV of 1.2 % has been achieved. Analysis of a femtomolar B-PE solution demonstrates that the bursts of photons from individual molecules can be baseline-resolved with 0.5 mW of laser power at a signal to noise ratio (SNR) of approximately 30, with approximately 100 photons detected from each molecule. A compact, low-power, high-sensitivity system detects DNA fragments as small as 125 bp or individual B-PE molecules in a flowing liquid stream. Demonstrated linearity, sensitivity, and resolution indicate that <1.0 mW of laser power is optimal, permitting further miniaturization of the system and additional cost reduction. Comprehensive analytical software exploits the standard cytometric paradigm of multiple 2D graphs and gating to extract features from classes of individually analyzed biomolecules. This complete system is thus poised to engage high-sensitivity applications not amenable to conventional flow cytometric instrumentation.

Ultra-violet resonance Raman spectroscopy for the rapid discrimination of urinary tract infection bacteria

The ability to identify pathogenic organisms rapidly provides significant benefits to clinicians; in particular, with respect to best prescription practices and tracking of recurrent infections. Conventional bioassays require 3–5 days before identification of an organism can be made, thus compromising the effectiveness with which patients can be treated for bacterial infections. We analysed 20 clinical isolates of urinary tract infections (UTI) by ultra-violet resonance Raman (UVRR) spectroscopy, utilising 244 nm excitation delivering ∼0.1 mW laser power at the sample, with typical spectral collection times of 120 s. UVRR results in resonance-enhanced Raman signals for certain chromophoric segments of macromolecules, intensifying those selected bands above what would otherwise be observed for a normal Raman experiment. Utilising the whole-organism ‘fingerprints’ obtained by UVRR we were able to discriminate successfully between UTI pathogens using chemometric cluster analyses. This work demonstrates significant improvements in the speed with which spectra can be obtained by Raman spectroscopic techniques for the discrimination of clinical bacterial samples.

Structural stability study of cobalt ferrite-based nanoparticle using micro Raman spectroscopy

Abstract Micro Raman scattering was used to study the structural stability of cobalt ferrite-based (CoFe2O4) nanoparticles, under illumination with the 514 nm line, at 7 mW laser power. Different samples were investigated after performing the steps of the magnetic fluid (MF) preparation. Raman spectra of samples peptized at 0.25 mol/l perchloric acid showed features similar to bulk maghemite. However, samples peptized at 0.75 mol/l perchloric acid showed features similar to the Fe3O4 phase.

Micro-Rotation by Flow-Induced Torque in an Optical Trap

We report a new, simplified mechanism for performing micro-rotation. A sample chamber filled with aqueous solution and mounted on a piezoelectric transducer (PZT)-driven stage was used to produce flow-induced torque for rotating micro-objects. We demonstrated the scheme by rotating ellipsoidal yeast particles and a two-sphere system with 20 mW of laser power. Clockwise or counterclockwise rotation could be controlled by changing the initial angular position of the object trapped and by reversing the direction of the PZT-driven stage. This mechanism has potential applications in microfabrication, biotechnology and fluidic technology.

Performance of a rotating aperture for spinning and orienting objects in optical tweezers

The spinning of asymmetric objects trapped within optical tweezers that have a rotating rectangular aperture inserted into the trapping laser beam is characterized. The measured maximum rotation rates of various asymmetric micron-sized objects are in agreement with a linear dependence on laser power. Maximum rotation rates of up to 0.2 Hz per mW of laser power suggest that rotation rates in the region of 10–20 Hz should be readily achievable in commercially available tweezers that have been modified by the inclusion of a rotating rectangular aperture. In addition, the possibility to alter the orientation of the aperture allows convenient control over the orientation of tweezed objects.

Numerical and Engine Cycle Analyses of a Pulse Laser Ramjet Vehicle

A preliminary feasibility study of a laser ramjet SSTO has been conducted using engine cycle analysis. Although a large amount of laser energy is lost due to chemically frozen flow at high altitudes, the laser ramjet SSTO was found to be feasible with 100 MW laser power for 100 kg vehicle mass and 1 m2 vehicle cross-section area. Obtained momentum coupling coefficient, Cm, was validated by means of CFD. As a result, the engine cycle analysis was under-estimating Cm. This would be because of the strong unsteady energy input in the actual heating process and the spatially localized pressure on the afterbody.

Sharp2Eupconversion luminescence ofCr3+inY3Ga5O12codoped withCr3+andYb3+

We report on upconversion luminescence in ${\mathrm{Y}}_{3}{\mathrm{Ga}}_{5}{\mathrm{O}}_{12}$ codoped with ${\mathrm{Cr}}^{3+}$ and ${\mathrm{Yb}}^{3+}.$ This is, to our knowledge, the first upconversion process directly involving ${\mathrm{Cr}}^{3+}.$ At low temperature excitation around 10 314 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ leads to relatively strong red luminescence in the title compound. The sharp upconversion luminescence around 14 300 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ is identified as the ${}^{2}{E}^{4}{A}_{2}$ transition of ${\mathrm{Cr}}^{3+}.$ The upconversion excitation spectrum follows the ${\mathrm{Yb}}^{3+}$ ${}^{2}{\stackrel{\ensuremath{\rightarrow}}{{F}_{7/2}}}^{2}{F}_{5/2}$ absorptions in the range 11 200--10 315 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. From transient measurements the upconversion mechanism is found to be dominated by an energy transfer step: Two excited ${\mathrm{Yb}}^{3+}$ ions simultaneously transfer their excitation energy to the ${\mathrm{Cr}}^{3+}$ ion. In ${\mathrm{Y}}_{3}{\mathrm{Ga}}_{5}{\mathrm{O}}_{12}:2%$ ${\mathrm{Cr}}^{3+},$ 1% ${\mathrm{Yb}}^{3+}$ the efficiency of the process at 10 K and for 150 mW laser power is 6% and decreases with increasing temperature due to intrinsic loss mechanisms of the system.

Recent Studies of Optical Limiting, Image Processing and Near-Infrared Nonlinear Optics with Nematic Liquid Crystals

The mechanisms for recently observed optically induced refractive index changes in nematic liquid crystals, and their use in novel optical limiting and image processing are reviewed, along with an assessment of their potentials for applications. We have also studied the optical nonlinearities of nematic liquid crystals in the near IR communication spectral region [1.55 µm]. Phase modulation of several π's can be generated with mW laser power in micron thick films.

Nonlinear Optical Effects in Nematic Liquid-Crystal Films in the 1.55 µm Spectral Region

We have studied the optical nonlinearities of nematic liquid crystals in the near IR communication spectral region [1.55 µm]. The origins of the refractive index changes are thermal indexing effect and director axis reorientations. Very large refractive index and phase modulation of several π's can be generated with mW laser power in micron thick dye-doped nematic liquid crystal films.

Flow cytometric sperm sorting: effects of varying laser power on embryo development in swine.

This study was conducted to determine fertilization rate and embryo development using the Beltsville Sperm Sexing Technology with two different laser power outputs, 25 and 125 milliwatts (mW). Freshly ejaculated boar semen was diluted; one aliquot was not stained or sorted (nonsort) and a second aliquot was stained with Hoechst 33342 and sorted as a complete population, not separated into X and Y populations (all-sort). Ovulation controlled gilts were surgically inseminated with 2 x 10(5) spermatozoa (44-46 hr after human chorionic gonadotropin (hCG)) into the isthmus of each oviduct, one oviduct receiving nonsort and the other all-sort at 25 or 125 mW. A total of 426 embryos were flushed from oviducts at slaughter 43 hr after laparotomy and prepared for determination of fertilization and cleavage rates using confocal laser microscopy for analysis of actin cytoskeleton and chromatin configuration. The percentage of fertilized eggs and embryos was less for the 25 mW all-sort compared to nonsort or the 125 mW all-sort (77.9 vs. 96.3 and 96.2%, P < 0.05). The percentage of fragmented embryos was greater for the 25 mW all-sort than the nonsort (15.2 vs. 4.5%, P < 0.05), but did not differ significantly from 125 mW all-sort mean (7.2%). The percentage of normal embryos (80.4% overall) did not differ (P > 0.05) among treatments. However, the rate of embryo development was slower (P < 0.05) after insemination with the 25 mW all-sort spermatozoa compared to nonsort spermatozoa. Embryos in the 3-4 and 5-9 cell stages for the 25-mW all-sort and nonsort were 78 and 20% vs. 49 and 50%, respectively. The embryo percentages for the 125 mW (3-4 and 5-9 cell stages, 59 and 35%) did not differ significantly (P > 0.05) from the nonsort or 25 mW all-sort. We conclude that the use of 125 mW laser power for sorting boar spermatozoa is advantageous to maintain high resolution separation and has no detrimental effect on embryo development compared to 25 mW.

Micro-probe raman studies of the dynamics of liquid crystals

We present a modified version of a Raman microspectroscope designed for dynamical studies of thin liquid-crystalline films in glass cells. This system is based on a confocal geometry and a multi-channel liquid nitrogen cooled CCD detector. The confocal arrangement makes possible the study of volumes only a few μm3 in size within a liquid-crystal cell with an axial resolution of 14 μm. The multi-channel detector allows high quality spectra to be recorded in a few seconds with less than 10 mW of laser power at the sample. Using an electrooptic modulator, dynamic studies can be done on a microsecond time scale. We present results obtained during the electrical switching of a anti-ferroelectric liquid-crystalline low molar mass organosiloxane material.

Identification of intraocular lens materials using confocal Raman spectroscopy

PurposeTo develop and test a noninvasive method to identify intraocular lens (IOL) materials in vitro. SettingCenter for Biomedical Engineering and the Department of Ophthalmology, University of Texas Medical Branch, Galveston, Texas, USA. MethodsA laser confocal Raman spectroscopy system (Conforam) was used for the noninvasive assessment of Raman spectra in the lower and the higher spectral regions (299.1 to 1833.7 cm–1 and 2633.8 to 3819.6 cm–1, respectively) of 4 IOL materials: silicone, poly(methyl methacrylate) (PMMA), acrylic, and hydrogel. ResultsEach lens material showed a distinctive spectrum in both the higher and the lower spectral regions. Most materials had unique peaks and a distinct profile using 1 mW of laser power and a 1 second exposure time. All materials still had a unique spectrum in both the higher and the lower region that allowed 1 material to be distinguished from the others. ConclusionsA Conforam differentiated silicone, PMMA, acrylic, and hydrogel lenses in vitro. Raman spectroscopy using the Conforam may provide a fast, safe, and reliable noninvasive method to gain information about the material of an implanted IOL and the stability of lens materials and their coatings.

A high-performance CO2 laser heterodyne detector operating at 250 K

The design, construction and assessment of a CO2 laser heterodyne receiver based on a Hg1-x Cd x Te heterostructure is described. The structure has been designed to minimize the leakage currents at high temperatures while maintaining a high quantum efficiency. Measurements show that over 4dB of shot noise can be obtained with the application of less than 1 mW of laser power. This result can be combined with the measured low-frequency quantum efficiency of 42% to give a noise equivalent power of 7.2 × 10−20 WHz−1. The device is mounted on a single-stage thermoelectric cooler and coupled to an amplifier. It is hoped that the availability of high-performance detectors which do not need to be cooled to cryogenic temperatures will greatly improve the attractiveness of laser heterodyne systems.

A broad emitter diode laser system for lithium spectroscopy

Li atoms. With 70 mW of laser power, 107 atoms have been loaded from a nearby thermal source.

Laser power effects on the Raman spectrum of isolated diamond chemical vapor deposition particles

In the present work the effect of incident laser power on the Raman spectra of diamond isolated particles and continuous films deposited on silicon and glassy carbon (GC) substrates by the chemical vapor deposition method is investigated. It is shown that the Raman line position measured for diamond particles shifts to lower wave numbers as a function of incident laser power. These shifts were most drastic for single particles deposited on GC that were examined using a Raman microprobe. In this case the diamond peak displayed a negative shift of ∼18 cm−1 when the laser power output was increased from 1 to 15 mW. The laser beam diameter was ∼2 μm and the diamond particle measured was 3–6 μm in diameter. Micro-Raman measurements of diamond particles deposited on a silicon substrate or continuous diamond films on GC display very small changes in the diamond Raman peak wavelength for the same laser power range. From our studies it is concluded that the negative shift of the Raman peak position is caused by laser-induced local heating of the irradiated diamond particles. The temperature under the laser spot was calculated from the intensity ratio of Stokes to anti-Stokes Raman lines measured as a function of laser power output. The Raman peak wavelength calculated for each temperature showed excellent agreement with our experimental results. The local temperature of an isolated diamond crystal on GC rises to ∼1000 K at 15 mW laser power output, whereas the temperature change of the continuous film on GC and of a single particle on silicon was in the 0–30 K range above room temperature for the same laser power output range. This difference in heating is explained on the basis of efficient heat dissipation through a large contact area between the deposited particles and the substrate surface in the case of single particles deposited on silicon or through grain boundaries in the case of the continuous film on GC. The inefficient heat dissipation from the isolated diamond particles on GC is related to the small contact area between the diamond crystals and the GC substrate as a result of etching during the deposition process and possibly to the presence of an amorphous component in the diamond crystals deposited.