Diode Laser Beam Research Articles

Genetic Algorithm Inversion of Dual Polarization Polar Nephelometer Data to Determine Aerosol Refractive Index

A polar nephelometer that measures the light scattered into a two dimensional plane by a stream of aerosols that intersect a 350 milliwatt diode laser beam with a wavelength of 670 nm is described. A half wave plate is used to orient the laser light both parallel and perpendicular to the measurement plane. This scattering information combined with simultaneously measured size distribution information is used to determine the real (mr) refractive index of the aerosols using a Genetic Algorithm search method. Errors in the retrieved mr based on noise in the scattering measurement as well as uncertainties in the size distribution measurement are examined. The mr of polystyrene latex spheres and ammonium sulfate droplets are determined and match expectations within experimental uncertainties using Mie-Lorenz theory. The angular scattering properties of spherical secondary organic aerosols generated by oxidizing α -pinene do not follow this theory and calls into question the inferred mr.

Absolute frequency measurement of the lithiumDlines: Precise determination of isotope shifts and fine-structure intervals

We use a Rb-stabilized ring-cavity resonator to measure the frequencies of the D lines in $^{6,7}Li.$ Li spectroscopy is done by exciting a well-collimated atomic beam with a perpendicular diode laser beam and monitoring the resulting fluorescence. We obtain frequencies of 446 789 597.791(30) MHz and 446 800 132.006(25) MHz for the $D_1$ line and 446 799 650.653(60) MHz and 446 810 184.005(33) MHz for the $D_2$ line in the two isotopes. These values are consistent with earlier measurements, but represent an order-of-magnitude improvement in uncertainty. The measurements allow us to determine precisely the isotope shift in the D lines and the fine-structure interval in the $2P$ state, which resolve several discrepancies among earlier measurements. The small negative isotope shift in the interval appears inconsistent with theoretical estimates.

Laser diode beam shaping with GRIN lenses using the twisted beam approach and its application in pumping of a solid-state laser

We report a novel beam shaping method for laser diodes based on the concept of twisted Gaussian Schell-model beams using GRIN lenses. This method enables a more symmetric pump as well as a compact setup for pumping of solid-state lasers. In the experiment with a standard 2 W diode, the beam quality factors in the two orthogonal directions were equalized to M x 2 ≈ 24 and M y 2 ≈ 18 , respectively, which pumped an intra-cavity frequency-doubled Nd:YAG laser at 946 nm with an output of 28 mW at 473 nm.

Collimation test of a corrected laser diode beam using lateral shearing interferometer

A lateral shearing interferometer is used for testing and verifying the collimation of a corrected laser diode beam. The laser diode beam is corrected to be circular and free from astigmatism using a previously proposed lens correcting system.

Ultra-precision machining of reflector array for laser diode beam shaping

Ultra-precision machining is an effective approach to achieve high dimension accuracy and surface finish required in optical and laser components. An extensive study using a two-axis diamond turning machine is conducted to machine the reflector arrays used for laser diode beam shaping. To position the workpiece precisely, theoretical analysis is made so that the dimensional accuracy can be achieved. Investigations into machining burr reduction are carried out. With the process developed, reflectors with optical surface finish of 8 nm in Ra and minimized burr size of less than 0.5 μm have been achieved.

Hyperfine Structure of 27Al by High-Resolution Ultraviolet Laser Spectroscopy

The high-resolution ultraviolet (UV) laser spectroscopy of 27Al has been performed by the frequency doubling of a tunable diode-laser beam together with a collimated atomic beam. Hyperfine structure spectra have been observed for two UV transitions in Al I, namely, 3s23 p2P1/2–3s24s2S1/2 at 394.401 nm and 3s23 p2P3/2–3s24s2S1/2 at 396.152 nm. The hyperfine structure constants A and B of 27Al have been determined for the 3s23 p2P1/2,3/2 and 3s24s2S1/2 levels, and compared with previously reported results.

Laser Transmission Welding of a Lap-Joint: Thermal Imaging Observations and three–dimensional Finite Element Modeling

Laser transmission welding (LTW) is a relatively new technology for joining plastic parts. This paper presents a three-dimensional (3D) transient thermal model of LTW solved with the finite element method. A lap-joint geometry was modeled for unreinforced polyamide (PA) 6 specimens. This thermal model addressed the heating and cooling stages in a laser welding process with a stationary laser beam. This paper compares the temperature distribution of a lap-joint geometry exposed to a stationary diode laser beam, obtained from 3D thermal modeling with thermal imaging observations. It is shown that the thermal model is capable of accurately predicting the temperature distribution when laser beam scattering during transmission through the polymer is included in the model. The weld dimensions obtained from the model have been compared with the experimental data and are in good agreement.

A randomized, prospective study comparing laser-assisted hatching and assisted hatching using acidified medium

To compare the clinical outcomes of patients whose transferred embryos underwent either laser-assisted hatching or hatching with acidified medium. Randomized, prospective, double-blinded study. University-based IVF center. Clinical outcomes following IVF were compared in 159 patient cycles who randomly had all transferred embryos undergo laser-assisted hatching (Laser; n = 57) or hatching with acidified medium (Acid; n = 54). Patients whose embryos had zonae thickness <13 mum were not hatched (Thin; n = 8) and patients with > or =4 embryos at the 7- to 8-cell stage or higher on Day 3 were transferred on Day 5 (Day 5; n = 40). Implantation rates, clinical pregnancy rates, ongoing pregnancy rates, multiple pregnancy rates. No significant differences were noted in clinical, ongoing, or multiple pregnancy rates between the four groups. The implantation rate for Day 5 transfers was significantly greater than both the Laser and Acid treatment groups. The use of a 1.48-micron infrared diode laser beam provides a safe and rapid method for performing assisted hatching and did not have a negative impact on patient care when compared to outcomes achieved using acidified medium.

Photo-induced effects in chalcogenide thin films under irradiation by synchrotron light

We present the results of measurements of changes occurring in chalcogenide thin films of Ge 30Se 70 and Ga 40Se 60 alloys induced by photo-absorption of visible and VUV light. Emphasis is given to the description of the experimental techniques, as well as the apparatus constructed for the measurements. The Ge 30Se 70 and Ga 40Se 60 alloys, were prepared by mechanical alloying in a ball mill, deposited as a thin film on a glass substrate and exposed to synchrotron photons in the visible and ultraviolet. The dependence of the transmission of a diode laser beam was determined as a function of the radiation exposure time used.

Non-equiphase Hermite–Gaussian model of diode laser beams

A non-equiphase Hermite–Gaussian model is proposed to describe the field in the plane parallel to the junction of double-heterostructure (DH) diode laser beams. The analytical expression for the far field of DH diode laser beams is derived and used to compare the calculated intensity profiles with the measured and calculated values given by Nemoto and Zeng et al., showing a further improvement between the calculated and measured profiles by using the non-equiphase Hermite–Gaussian model.

Atomic beam focusing with a curved magnetic mirror

Reflective atom optics has been experimentally realized with a continuous flux of cold atoms by using a magnetized videotape. We have studied the behaviour of a slow atomic beam with a velocity of 20 m s−1 incident at different angles on the surface of a curved magnetic mirror. Focusing of the beam has been demonstrated and this induces an amplification up to a factor 3 of the fluorescence emitted by the atoms around the focal point. We deduced the shape of our reflector from the focal length measurements and show that the result is completely consistent with those obtained from the reflection of a red diode laser beam on the curved mirror.

Henry Granjon Prize Competition 2006 Co-Winner, Category A “Joining and fabrication technology” Models for Diode Laser Transformation Hardening of Steels

Diode laser beam transformation hardened surfaces have been studied in order to develop models for estimating the hardness and depth of the transformed region. The surfaces of low alloy and martensitic stainless steels have been transformation hardened in inert and oxidising atmospheres to establish the dependence of processing parameters and oxidation on the absorptivity of steel surfaces. It was found that the absorptivity varied between 35 to 85%, depending on the oxide formation on the surface. A model for estimating the depth of the hardened region was developed. The model utilises data established by absorption experiments, and the variation of absorptivity with processing parameters is approximated in the model. Validation was carried out by measuring the hardened depth from transverse cross sections of processed samples and comparing the results to data obtained by the model. A good estimation of the hardened depth was achieved when the traverse rate was equal to or above 3.3 mm s−1. Hardening experiments were performed to 34 commercial steel grades. 7 steels were studied in detail to establish the phase transformations occurring during the hardening process. Based on these experiments, a model for calculating the surface hardness was developed. The model takes data from equilibrium diagrams. A kinetic term to express the rate of change during hardening was introduced to relate equilibrium data to the non-equilibrium process. A good correlation between the model and experimental results was achieved with all materials, excluding martensitic stainless steels. Developed models are applicable, within the established limits, for most commonly hardened steels and processing parameters. The presented model for calculating the hardened depth is not bound to the laser and beam type used in the experiments. Input data for estimating the absorptivity and heat flow is based on the beam-material interaction time and laser power on work piece surface. It can, thereby, easily be converted to be used with other diode laser sources. Correspondingly, input data for the hardness calculations is obtained from pyrometric measurement and is not, thereby, limited to the laser type, wavelength, beam profile or processing parameters.

Time-multiplexing generates a diode laser beam with high beam quality

The beams of four pulsed high-power laser diodes are time-multiplexed resulting in a laser beam of high quality. A combination of polarization switches and filters forming a digital time-multiplexer is utilized to guide laser pulses produced by the individual laser diodes onto a common optical path. A resulting beam with an optical power of 10 W and a beam quality comparable with that of a single laser diode at a wavelength of 960 nm is obtained.

Laser/sol–gel synthesis: a novel method for depositing nanostructured TiN coatings in non-vacuum conditions

In this work results of experiments on the in situ production of titanium nitride by the reaction of titania sol-gel with a nitrogenous admixture under laser irradiation are reported. A diode laser beam at different powers and traverse speeds was applied to the mixture placed on EN43 mild steel and 316L stainless steel substrates. Composite coatings of titanium nitride and titanium oxide with a hardness of 17-21 GPa have been achieved by this new method. Surface morphology and microstructure of the deposited coatings and substrate surface layers were examined using optical microscopy, scanning electron microscopy, and field-emission gun scanning electron microscopy. Chemical composition was determined by energy-dispersive X-ray analysis. The phases were identified by X-ray diffraction. Results of microhardness and nanohardness at the top surface were evaluated.

Analysis of error yielded by scalar approximation to the properties of laser diode beams

Based on the vector Rayleigh-Sommerfeld far-field diffraction integral formula, a vector model for describing the far field of a laser diode is proposed beyond the paraxial approximation. Through the analysis of the error yielded by the scalar approximation to the properties of laser diode beams, it is found that the error is only correlative with propagation distance and the coordinate perpendicular to the junction plane, and there is a certain relationship between the error and a space angle.

Resonant Reaction in Rb–Cs Vapour Mixture Rb(5P1/2) + Cs(6P3/2) → Cs(8S1/2) + Rb(5S1/2)

We experimentally study energy-pooling collision in the Rb–Cs vapourmixture at low densities in a cell. Atoms are excited to Rb(5P1/2)and Cs(6P3/2) states using two single-mode diode lasers. To isolatethe heteronuclear contribution in the fluorescence spectrum, adouble-modulation technique is adopted. The excited-atom density andspatial distribution are mapped by monitoring the absorption of acounterpropagating single-mode diodelaser beam, tuned to Rb(5P1/2→7S1/2) andCs(6P3/2→8S1/2) transitions, respectively, which could betranslated parallel to the pump beams. The excited atom densities arecombined with the measured fluorescence ratios to determine crosssection for the energy-pooling process [i.e. Rb(5P1/2) + Cs(6P3/2) → Cs(8S1/2) + Rb (5S1/2)].The cross section is 3.79×10−14 cm2±45%.

Study of Microstructure in Surface-Melted Region of Ni-Base Single Crystal Superalloy CMSX-4

This work investigated microstructure in the surface-melted region of Ni-base single crystal superalloy CMSX-4 by using a diode laser beam as a heating source. Such processing parameters as laser power and scanning speed in laser surface melting were varied while defocusing distance and shielding gas (Ar) flow rates were fixed. Specimen surfaces were arranged parallel to the (001) of base alloy. The microstructure in the melted region was analyzed by optical microscopy and SEM. Crystal orientation of the melted region was analyzed using electron backscattered pattern analysis. The microstructure was remarkably changed when the heat input of surface melting was varied. The surface-melted region was found to solidify into a single crystal with directional dendrites that grew along the [001] directions under low heat input conditions. The surface-melted region was also a single crystal with disoriented dendrites that grew along the [100] or [010] directions under medium heat input conditions. In contrast, the melted region consisted of poly crystals with stray crystals under high heat input conditions. Such tendencies were also observed in the melted region with gas tungsten arc. These results demonstrate that the surface-melted region can solidify into a single crystal under conditions in which larger temperature gradient and higher solidification rates can be achieved.

Development of High-Performance Laser Diode for Pumping Solid-State Laser

The spectral bandwidth of a broad-area laser diode is effectively suppressed by use of an off-axis external-cavity technique. The external cavity consisted of a rod lens, a cylindrical lens and a volume Bragg grating. The laser beam has 5.8-fold improvement in spectral bandwidth and its peak power versus wavelength is effectively enhanced. On the basis of this technique, we focus the beam of the high-power laser diode to effectively end pump a solid-state laser.

An experimental study of micromachining step-mirrors for laser-diode beam shaping

Micro and ultra-precision machining is an effective approach to achieve the high-dimensional accuracy and surface finish required in optical and laser components. In this paper, an extensive study using a two-axis diamond turning machine is conducted to machine the step-mirrors used for laser-diode beam shaping. To position the workpiece precisely, theoretical analysis is made so that dimensional accuracy can be achieved. Investigations into machining burr reduction are carried out. With the process developed, step-mirrors with an optical surface finish of 8 nm in Ra and a minimized burr size of less than 0.5 µm are achieved.

Examination of laser hardened steel surfaces using interference microscopy

A diode laser beam in the near-infrared region is absorbed more efficiently by a metal surface than a CO2 or a Nd:yttrium-aluminum-garnet laser beam. Diode laser transformation hardening without an absorptive coating is feasible even in an inert gas atmosphere. Absence of the absorptive coating, and the fact that the formation of an oxide layer is inhibited, makes it possible to study phase transformations occurring during hardening from the surface relief formed to the processed surface. In the present study diamond polished plain carbon and low alloy steel samples have been hardened in an inert gas atmosphere of argon using a high power diode laser. Surface reliefs caused by phase transformations during quenching have been examined using differential interference contrast (DIC) microscopy. Hardness of each sample was measured and the effect of the processing parameters on the surface hardness and microstructure has been established. DIC imaging was found to be a rapid and illustrative tool for examining microstructures in laser hardened surfaces. Extent of martensite, austenite grain size prior to quenching, and martensite lath size are visible in the DIC images.