CO2 Laser Probe Research Articles

Timing and duration of Archean orogenic gold deposits in the Bourlamaque pluton, Val d’Or mining camp, Abitibi, Canada

In the Val-d’Or mining district of the Archean Superior Province, the relationship between regional metamorphism/deformation and the timing of orogenic vein-type gold mineralization is debated; some authors arguing that gold mineralization was coeval with the regional D2 deformation event and broadly synchronous with metamorphism, and others suggesting that it is 60 to 100 Ma younger than peak metamorphism. Using the 40Ar/39Ar method and the compilation of U-Pb or Pb-Pb ages of ore-related minerals, this contribution presents a geochronological study on the timing and the inferred duration of the formation of vein-type gold deposits hosted by the Bourlamaque pluton in the Val d’Or mining district. We present an extensive set (49 samples) of 40Ar/39Ar CO2 laser probe data acquired on amphibole and white mica single grains from three major gold deposits, the Lac-Herbin, Beaufor and Beacon-2 mines. In each deposit, gold mineralization is host by shear and extensional quartz veins associated to steeply south-dipping networks of ductile shear zones. Barren north-dipping faults also occur at each deposit and are attributed to post-mineralization structural event(s). Amphiboles 40Ar/39Ar analyses yield magmatic crystallization ages clustering around 2704 Ma and preserve evidences for at least two subsequent disturbances linked to probable hydrothermal circulation events at c. 2667 Ma and c. 2652 Ma. White micas 40Ar/39Ar age spectra from auriferous quartz veins and hosting mylonitic shear zones are typical of long-lasting and sequential dynamic recrystallization and suggest that Au-bearing hydrothermal circulation was establish, at least, around c. 2650 Ma, and followed by a succession of hydrothermal pulses at c. 2597, 2575, 2551, 2500 and 2452 Ma. 40Ar/39Ar ages distribution among the different deposits as well as between the auriferous quartz veins and hosting shear zones are consistent with fluids production and circulation along an active network of seismically active fault zones.

Prospective control trial: flexible CO2 laser vs. monopolar electrocautery for robotic microsurgical denervation of the spermatic cord.

Microsurgical denervation of the spermatic cord (MDSC) is a treatment option in patients with chronic orchialgia. This procedure requires precise care to avoid any thermal damage to crucial adjacent tissues (arteries, veins, and lymphatics). Monopolar electrocautery is the standard ligation energy source, but may cause extensive collateral damage to the tissues. However, CO2 laser is known to produce a very predictable tissue penetration and minimal collateral spread. The goal of this study was to compare the extent of collateral thermal damage in both monopolar electrocautery and CO2 laser ablation in the spermatic cord during a robotic assisted MDSC (RMDSC) procedure as well as the feasibility for utilizing the flexible fiber-optic CO2 laser probe after "RMDSC" procedure. RMDSC was performed using standard monopolar electrocautery on the spermatic cord of one side of a fresh human male cadaver (randomly selected) and then compared to RMDSC using the CO2 laser on the contralateral spermatic cord. Nine histological cross-sections from each cord were measured for depth of collateral thermal/cautery injury. The mean collateral thermal injury with CO2 laser was 0.17 ± 0.031 mm (range: 0.15-0.25 mm), and with standard electrocautery 0.72 ± 0.046 mm (range: 0.60-0.75 mm). CO2 laser resulted significantly less collateral thermal injury than standard electrocautery (p < 0.0001). The CO2 laser probe was easy to manipulate with the Black Diamond micro-forceps (Intuitive Surgical, CA) and allowed for convenient tissue plane dissection. Human cadaveric targeted RMDSC using a flexible CO2 laser energy results in significantly decreased collateral thermal injury compared to standard monopolar electrocautery. These initial findings suggest potential advantages of the CO2 laser over traditional monopolar cautery in cases requiring minimal collateral tissue damage. Future studies are needed to assess its clinical potential in microsurgery.

Supergene manganese ore records 75 Myr-long Campanian to Pleistocene geodynamic evolution and weathering history of the Central African Great Lakes Region – Tectonics drives, climate assists

The southeastern part of the Democratic Republic of the Congo locally hosts Proterozoic manganese deposits. The deposits of Kisenge-Kamata are the most significant, but manganese ores are also known to occur at Kasekelesa (former Katanga Province) and Mwene-Ditu (former Kasai Province). For the present study, cryptomelane-rich samples from these two localities were dated, using the 40Ar/39Ar step-heating method with a CO2 laser probe. The ages obtained are within a range of c. 77 Myr to c. 2 Myr. Cryptomelane formation took place at c. 76.4 Ma, c. 59.6 Ma, c. 45 Ma, c. 35 Ma, c. 23.8 Ma, c. 15.4 Ma, and c. 13.3 Ma at Kasekelesa, and it occurred at c. 35 Ma, c. 22.4 Ma, c. 15 Ma, c. 5.5–7.2 Ma, c. 3.6 Ma, and c. 2.1–2.3 Ma at Mwene-Ditu. The Campanian age (c. 76.4 Ma) recorded at Kasekelesa is the oldest 40Ar/39Ar age that has up to now been recorded for Mn ores from Africa. It documents the formation of oxidized ore along a Campanian or older erosion surface, which could be part of the ‘African Erosion Surface’. The complete age record suggests that continent-wide tectonics accounts for most of the recognized supergene ore formation episodes, controlled by vertical lithospheric movements that are ultimately responsible for alternating stages of landscape stability and erosion. Tectonics is thus regarded as the first-order control for secondary ore formation in Central Africa, over the last 80 Myr. Climate is a second-order control, because sufficient water supply is needed for supergene enrichment, whereby climatic conditions are recognized to have been favourable during some relatively cold Late Mesozoic and Paleogene periods, as well as during some humid and warm Neogene stages.

Laser‐probe 40Ar/39Ar dating of strain fringes: Mid‐Cretaceous synconvergent orogen‐parallel extension in the interior of the Sevier orogen

UV and CO2 laser‐probe 40Ar/39Ar in situ analyses of phlogopite and muscovite in fibrous strain fringes from greenschist‐facies metamorphic rocks document mica growth ages at temperatures lower than their closure temperatures, and therefore directly date deformation. The new dates resolve the age of the earliest ductile fabric recorded in the Raft River–Albion–Grouse Creek metamorphic core complex of Utah and Idaho. Phlogopite was dated in quartz‐calcite‐phlogopite strain fringes around pyrite in Pennsylvanian‐Permian rocks from the Grouse Creek Mountains (Utah) using both the UV and CO2 laser probe; muscovite was dated in quartz‐muscovite strain fringes around pyrite in deformed Jurassic sills from the Black Pine Mountains (Idaho) using the CO2 laser probe. Phlogopite 40Ar/39Ar ages for individual strain fringes (Grouse Creek Mountains) range from 92 Ma to 110 Ma, with the most reliable ages ranging from 101 Ma to 110 Ma (mean age, 105.0 ± 5.8 Ma). Muscovite 40Ar/39Ar ages for individual strain fringes (Black Pine Mountains) range from 97 Ma to 112 Ma (mean age, 104.7 ± 5.8 Ma). Strain fringes are associated with a subhorizontal foliation and a generally N‐trending elongation lineation exhibiting components of top‐to‐the‐north simple shear and coaxial strain accommodating N‐S extension and subvertical shortening. Midcrustal northward flow at 105 (±6) Ma within the interior of the Sevier orogen, coeval with east‐directed shortening in the foreland and with plate convergence, records orogen‐parallel synconvergent extension. We favor gravitational relaxation of structural culminations resulting from focused crustal shortening as a driving mechanism for orogen‐parallel flow.

Instrumental Capabilities and Limitations of Two-Dimensional Phase Contrast Imaging on LHD

A novel phase contrast imaging is employed for diagnostics of plasma density fluctuations on LHD. With the use of two dimensional 48 ch (6×8) detector array and CO2 laser probe beam this technique permits observation of radial profiles of density fluctuation during a single discharge either within the entire plasma diameter in overview mode or within some fraction of the diameter in zoom mode. The velocity of density fluctuations in laboratory frame can be determined simultaneously with fluctuations of velocities. Analysis of system performance was made with the use of numerical calculations. The targets for the analysis include wave number and spatial resolution of the method, contrast of instrumental function, which is determined by low k signal leakage into the high k spectral region, and focal depth of the optical system for different fluctuation wave numbers. The role of shortcomings of optical system like distortion of the optical front by diffraction is studied. Suggestions for future upgrade of the diagnostics are advanced.

Immediate retinal adhesion by CO2 laser irradiation using a fiberoptic intraocular probe.

Using an experimental fiberoptically guided CO2 laser system, we produced lesions on fresh bovine retinas. These lesions were shown to achieve immediate measurable chorioretinal adhesion. This model provides preliminary data on the use of a fiberoptic CO2 laser probe to produce chorioretinal lesions and possible future use in intraocular surgery for retinal detachment. The advantages of using CO2 laser energy are minimal damage surrounding desired lesion and its versatility as a coagulator and cutter. With modifications, CO2 endolaser may have a role in intraocular surgery.

Diagnostics of the active media of homogeneous and mixed gasdynamic lasers using a CO2laser probe tunable between lines in conventional and unconventional bands

A cw CO2 laser probe, tunable between the lines of five bands (0001–1000, 0001–0200, 0111–1110, 0002–1001, and 0002–0201), was developed and used to test a laser spectroscopic method for investigating the active media of homogeneous and mixed gasdynamic lasers. The experimental values of the translational and vibrational temperatures and of the active-particle (CO2) concentration were compared with the calculated data. A satisfactory agreement was obtained.

Saturated absorption in SF_6 with double-velocity selection

Doppler-free saturated absorption of a weak CO(2) laser probe on SF(6), which is caused by two noncollinear pump beams, is reported. A small-linewidth angular dependence was observed and can be predicted in agreement with a fifth-order perturbation calculation for a two-level atom.

Experimental retinochoroidal tissue vaporization with a CO2 laser probe.

The immediate and chronic effects of an intraocular carbon dioxide CO2 laser probe used for tissue vaporization were studied in cynomolgus monkeys' eyes. Acute lesions produced necrosis (from superficial to deep) of the retina and choroid, depending on the amount of energy used. Chronic lesions showed disorganization of the retina and choroid, with scar formation. Extensive tissue vaporization produced tractional retinal detachment in the chronic stage. Tractional detachment was prevented if the area of CO2 laser application was previously encircled with argon laser scars.

Imaging methods for the observation of plasma density fluctuations

Imaging techniques offer attractive alternatives to small-angle Thomson scattering for scale lengths of density fluctuations causing diffraction in the Raman-Nath regime. This is the case for fluctuations with wavelengths above about 3 mm for Tokamak sized plasmas, when a CO2 laser probe beam is used. Four methods ('phase scintillation', phase contrast, wavefront shearing and interferometry) are compared, on the basis of their transfer properties. They offer new means of studying density fluctuations of magnitude up to the dimensions of the plasma, such as those associated with turbulence, magnetic islands, convective cells or driven waves. The long wavelength limitations are discussed in detail and are related to those encountered for far-field techniques. An experimental comparison of 'phase scintillation' and phase contrast is given, and the criteria relative to the depth of field of imaging instruments in this context are considered.

Saturation of N2F4 by a short CO2 laser pulse

Saturation parameters and absorption characteristics of N2F4 at 10.6 μm is studied using an intense 1.5 ns pump pulse and a low cw CO2 laser probe. It is found that, for short-pulse interaction, a four-level model describe satisfactorily the experimental results at pressure up to 120 Torr. The main parameters of the model are a rotational–rotational exchange constant of 47 ns Torr, a fundamental radiative cross section of 1×10−16 cm2, a contribution of 1/60 of the ground state population to absorption and a residual absorption coefficient equal to 20% of the small signal absorption at low pressure.

10.6 mu m Faraday rotation measurement of the azimuthal magnetic field in a Z-pinch plasma

The Faraday rotation of a plane-polarised CO2 laser probe beam passing along chords across an argon Z-pinch plasma, current 31 kA, has been measured and the azimuthal magnetic field Btheta calculated using 633 nm interferometric electron density measurements. The results are consistent with the total current being carried by the pinched discharge column, and confirm the validity of the technique.

Transient thermal blooming of single and multiple short laser pulses

Energy transfer through absorbing media with pulses short compared to the acoustic transit time has been investigated experimentally and theoretically for collimated beams in a homogeneous wind field. Two experimental approaches were used: a low intensity cw CO(2) laser probe beam technique giving a continuous record of the lensing of the medium following the transmission of a coaxial high power TEA laser pulse and a direct determination of high power pulse train blooming using a thermofax covered drum. The experimental results support the predictions of a geometric optics perturbation solution as well as those of existing propagation codes. An interesting case, namely, enhancement resulting in a 20-30% increase of the original nonbloomed peak intensity is observed when the pulse separation time is approximately 1-2 times the wind flow time across the beam.