Q-switched Neodymium Research Articles

Detection of optical emission from InSb induced by pulsed laser evaporation

The results of in situ measurements of the optical emissions which occur during the deposition of InSb films by pulsed laser evaporation are reported. Evaporation was induced by a Q-switched neodymium : yttrium aluminum garnet laser with 90 ns pulse width and powers less than 1.5 mJ per pulse at a wavelength of 1.06 μm impinging on the surface of a rotating single crystal InSb target. At low laser powers, emission lines characteristic of In and Sb species were detected which decayed in 800 ns. At higher laser powers, emissions from excited atoms and/or ions were observed. Surface contamination of the target reduced the power threshold to produce ions.

Phase-matched second harmonic generation by a surface polariton along a silver layer on a slab-type optical waveguide

Phase-matched second harmonic generation by a surface-plasmon polariton was observed along a silver layer on a slab-type optical waveguide with a Q-switched neodymium:yttrium aluminum garnet laser (1.064 μm). A numerical analysis previous to the experiment was carried out by a perturbation method employing the conception of coupled modes between surface polariton waves and guided waves. In this case the slab-type optical waveguide played the role of an energy storage layer to realize a longer macroscopic propagation length.

Laser flash effects on laser speckle shift visual evoked potential.

Steady-state visual evoked potentials (VEP's) were recorded from four cynomolgus monkeys in response to a sinusoidally oscillating 10 degrees helium-neon laser speckle field (632.8 nm), moving vertically 2.5 degrees at 8 shifts per second. A 5-pulse flash train at the maximum permissible exposure (MPE) dose from a collimated Q-switched frequency-doubled neodymium laser (532 nm) was superimposed on the foveal stimulus and the subsequent disruption and recovery of the VEP measured. Minimal disruption of the response signal magnitude was demonstrated (0.1 greater than p greater than 0.05) which recovered within 300 ms of the termination of the pulse train. A small but significant (p less than 0.01) disruption of phase entrainment was also noted that recovered within the same period. This is contrasted with a second experiment with three monkeys in which an argon (514 nm) laser served both as the speckle stimulus source and as the shuttered flash. Exposure to collimated MPE argon radiation for 250 ms immediately depressed the VEP (97%, p less than 0.01) and showed recovery to 70% of the pre-flash baseline only after 3 s. Phase lock was also severely degraded for several seconds. These results imply that visual processing of nonacuity-limited medium contrast stimuli with broad spatial frequency content will probably not be materially affected by ultra-short pulsed laser exposure at these energy levels and frequencies. However, even safe levels of collimated continuous laser light may have severe effects on vision that could parallel flash effects seen with Xenon discharge flash lamps.

Early clinical experience with a new generation Q-switched neodymium:YAG laser

We present early clinical results of Nd:YAG capsulotomy with a new generation Nd:YAG laser unit. We conclude that the new systems are as efficient as their early counterparts in noninvasive capsulotomy.

Effect of Pilocarpine in Treatment of Intraocular Pressure Elevation Following Neodymium:YAG Laser Posterior Capsulotomy

A prospective study was conducted in 30 eyes of 30 patients to determine if pilocarpine would prevent increased intraocular pressure following Q-switched neodymium (Nd):YAG laser posterior capsulotomy. Fifteen eyes were given pilocarpine 4%, immediately following laser therapy and every hour until bedtime. Fifteen eyes served as untreated controls. Our results show that without prophylactic therapy, 10 of 15 eyes (67%) had a post-laser intraocular pressure (IOP) elevation of >10 mmHg, while only one of 15 (6.6%) of the pilocarpine-treated eyes had a rise of that magnitude. The facility of outflow was reduced by 42% in the untreated eyes in contrast to an increase of 3% in those eyes treated with pilocarpine. Thus, pilocarpine 4% is effective in reducing the incidence and magnitude of elevated IOP following Nd:YAG posterior capsulotomy.

Early Complications Following Q-switched Neodymium:YAG Laser Posterior Capsulotomy

A prospective evaluation was conducted of Q-switched neodymium:YAG laser capsulotomy in 53 eyes followed for one postoperative month. The first 31 eyes were seen at two-hour intervals for the first eight hours, and the remaining eyes were checked only at the second postoperative hour during that day. Eighty-nine percent of eyes required a pulse setting of less than 1.7 mJ to successfully penetrate the posterior capsule. Visual acuity was improved in 91% of eyes.A transient immediate postoperative intraocular pressure (IOP) elevation was seen in over 75% of treated eyes, and one-third had an IOP elevation greater than 10 mmHg over the preoperative IOP. This elevation was most common in glaucomatous eyes and occurred in almost one-half of the treated eyes by the second postoperative hour. This IOP change did not correlate with the degree of inflammation, bleeding, anterior chamber debris, or total energy delivered. Minimal iris bleeding occurred in 9% of treated eyes and was associated with iridocapsular adhesions. Eighty-one percent of eyes with posterior chamber implants developed some degree of lens damage.

Flicker electroretinograms and visual evoked potentials in the evaluation of laser flash effects.

Electroretinograms (ERG's) and visual evoked potentials (VEP's) were recorded from four cynomolgus monkeys in response to a sinusoidally flickering argon laser beam (514 nm) producing a 50-micron spot on the fovea. Super-position of a 20-Hz train of six pulses of Q-switched (120 ns) frequency-doubled neodymium laser light (532 nm) at "safe" exposure energies in 250 ms had no significant effects on the ERG (p greater than 0.05). The VEP was disrupted significantly (p less than 0.001) but demonstrated recovery within 500 ms of the initial pulse. Therefore, flash effects of pulsed visible lasers at these doses on suprathreshold luminance processing are probably limited only to the exposure period.

A Comparison of Neodymium:YAG end Argon Laser Iridotomies

A prospective short-term clinical study evaluated argon and Q-switched neodymium:YAG laser iridotomies in 40 eyes of 20 patients with primary chronic angle-closure glaucoma. All patients had bilateral iridotomies with one eye randomly assigned to argon laser and the fellow eye to neodymium:YAG laser therapy. In all eyes a patent iridotomy was created in one treatment session. A mean of 12 ± 11 and 0.033 ± 0.025 J were needed for iridotomy formation in argon and neodymium:YAG treated eyes respectively. No neodymium:YAG and six (30%) argon iridotomies had marked closure requiring retreatment. Immediate postoperative intraocular pressure elevation greater than 10 mmHg was seen in seven (35%) argon and six (30%) neodymium:YAG-treated eyes. Nine (45%) eyes treated with the neodymium:YAG laser had bleeding from the iridotomy site. No acute lens damage was found in the neodymium:YAG eyes while seven (35%) lenses in the argon group had focal opacities. Seven (35%) neodymium:YAG and five (25%) argon treated eyes had focal nonprogressive corneal opacities above the iridotomy site. Specular microscopy showed a significant central corneal endothelial loss in argon laser treated eyes. No eyes had detectable retinal damage.

Q switched Neodymium:YAG Laser Iridotomy

Twenty phakic eyes of 19 patients underwent Q-switched neodymium:YAG laser iridotomies for angle-closure glaucoma. Eleven eyes were previous argon laser failures. Penetration was achieved in each case with several shots in one session. Complications were minor and transient.

Quantum well structures of In0.53Ga0.47As/InP grown by hydride vapor phase epitaxy in a multiple chamber reactor

A computer controlled multiple chamber chemical vapor deposition reactor, designed for the growth of InP based alloys, has been constructed. In this system, specular epitaxial layers of InP and In0.53Ga0.47As are grown in separate chambers. This allows for the uninterrupted growth of In0.53Ga0.47As/InP quantum well structures with layer thicknesses of approximately 150 Å. The photoluminescence spectra of these structures exhibit upward energy shifts as large as 71 meV from the band-gap energy of In0.53Ga0.47As. Laser action at 1.5–1.6-μm wavelengths has been obtained at temperatures up to 100 °C by optical pumping with a Q-switched neodymium:yttrium aluminum garnet laser.

Real-time measurement of picosecond optical pulses from an InGaAsP diode laser using an ultrafast streak camera with infrared frequency up-conversion

A novel method for real-time measurement of ultrashort optical pulses generated from InGaAsP diode lasers at the wavelength of 1.3 μm has been realized by means of an ultrafast streak camera incorporating a frequency up-conversion technique with a LiIO3 crystal pumped by a Q-switched neodymium: yttrium aluminum garnet (Nd:YAG) laser at 1.064 μm. The optical pulse from an InGaAsP double-channel planar buried heterostructure (DC-PBH) diode laser operated by a short pulse current of 1-ns duration was measured to have a full width at half-maximum (FWHM) of approximately 28 ps by single shot scanning with the temporal resolution of 8 ps. Using a 15-mm-long LiIO3 crystal and 500-W peak power of the pumping laser pulse focused at 400 μm in diameter, the up-conversion efficiency and minimum detectable peak power of the diode laser pulse at 1.3 μm were estimated to be approximately 0.65% and 1 mW, respectively. This technique can be widely utilized for real-time detection of ultrashort optical pulses in the wavelength range beyond 1–10 μm or more.

Direct measurement of the melt depth of silicon during laser irradiation

We have studied the change in morphology of laser irradiated silicon wafers by annihilating the oxygen thermal donors and the oxidation-induced stacking faults in order to verify the melting of the near-surface regions. The laser beam used was of 1.06 μm with a diameter of 40 μm, generated from a Q-switched neodymium:yttrium aluminum garnet (Nd:YAG) laser with a 150-ns pulse width and at a repetition rate of 12 kHz. Laser beam irradiation above about 6 J/cm2 annihilated both thermal donors and stacking faults, giving evidence of melting and suggesting that the annihilation of the thermal donors and of the stacking faults can be useful in studying the surface morphology in laser/electron beam irradiation.

Pulsed UV laser Raman spectroscopy of silane in a linear-flow chemical vapor deposition reactor

For the first time, spatially resolved relative concentrations of silane inside a chemical vapor deposition reactor have been measured with spontaneous Raman spectroscopy using the third harmonic of a Q-switched neodymium:yttrium aluminum garnet laser. Concentration profiles were obtained under both atmospheric and low total pressure conditions. Considerable depletion of silane in the gas phase was observed.

Increase in the transparency of water vapor in vacuum ultraviolet under the action of giant laser pulses

An experimental investigation was made of the interaction of radiation pulses from a Q-switched neodymium glass laser with water vapor. Pulse-like increase in the transparency of the vapor was observed at the wavelength of probe radiation in the range 185?187 nm; this increase in the transparency increased on increase in the energy of the interacting pulses. The effect was clearly due to two-stage photodissociation of the water vapor molecules in the region of intersection of the interacting and probe radiations.

Collision-induced I(52P1/2–52P3/2) radiative transition

An investigation was made of the dependences of the initial I(52P1/2)→I(52P3/2)+hν (λ = 1315nm) luminescence signal on the pressure and nature of the buffer gases. Atoms of I in the 52P1/2 state were formed, in initial concentrations of (0.5–3)×1016cm−3, as a result of photolysis of CF3I (0.01 atm) by the fourth harmonic of a Q-switched neodymium laser (E~0.6 J,τ ~2×10−3 sec). The I(52P1/2) luminescence was recorded by a germanium photodiode whose time constant was (3–4)×10−7 sec. When CF3I was diluted with Ar, Xe, and SF6 buffer gases, the intensity of the luminescence of the I(52P1/2) atoms increased because of an increase in the probability of the 52P1/2→52P3/2 transition as a result of collisions of the iodine atoms with the atoms or molecules of the buffer gases. The dependence of the probability of the investigated transition on the nature and pressure of the buffer gases was determined in the pressure range ~0–1 atm. Estimates were obtained of the oscillator strengths corresponding to the matrix elements of the induced electric dipole moment due to the deformation of the electron shells of the iodine atoms in collisions.

Subnanosecond periodicallyQ-switched neodymium glass laser

A train of pulses of approx.5 x 10/sup -10/ sec duration and approx.2 x 10/sup -3/ J energy was generated by a periodically Q-switched neodymium glass laser. The width of the emission spectrum was approx.3.0 nm and the contrast of the emitted radiation exceeded 10/sup 3/. Pulse generation started after 10--20 passes through the resonator. The pulses could be synchronized with external apparatus to within approx.10/sup -9/ sec. Stable generation of pulse trains was observed when the pumping rate exceeded considerably the threshold value. A laser of this kind could be used as a source of short pulses which could then be amplified effectively in high-power neodymium-glass systems.

Resonant-mode analysis of single-mode face pumped lasers

The theoretical investigations and experimental verifications of resonant modes of optically pumped solid host face-pumped lasers (FPL) are discussed. The conditions for a single transverse-mode operation for electrooptically Q-switched neodymium glass and YAG lasers are examined in both stable and stable/unstable resonator configurations. Resonant mode computations were made, based on a Gaussian quadrature and a complex non-Hermitian matrix program.

Pulse radiolysis and laser photolysis study of solvated electron solutions in hexamethylphosphortriamide

Laser photolysis ( Q-switched neodymium laser, 20 ns) and pulse radiolysis (2.2 μs electron pulses from a linear accelerator, dose per pulse ⋍2 krad) methods have been used in a study of the influence of light and ionizing radiation on electrochemically generated solvated electron solutions in hexamethylphosphortriamide (HMPA) at room temperature. The stoichiometry of association between e s - and metal cations (Na +) observed in the system is found to be (Na +, e 2 −2). It was found after a laser pulse that this complex with λ max = 750 nm is bleached and simultaneously a species absorbing in the i.r. (solvated electrons) is formed. The extinction coefficient of (Na +, e 2 -2) is 4 × 10 4 dm 3 mol −1 cm −1, the oscillator strength 0.7, and the quantum yield of photobleaching 0.075. The rate constant of (Na +, e 2 −2) formation K 1 = 1.2 × 10 6 dm 3 mol −1 s and the equilibrium constant between Na +, e s *minus; and the complex K ∗ = 2.3 × 10 4 dm 6 mol −2 .

Distribution of neodymium laser energy between modes

An experimental investigation was made of the spectral statistics of the radiation emitted by a Q-switched neodymium laser. The emission spectrum was recorded with a resolution equal to the model spacing. It was found that the density of the probability of the appearance of an axial mode of a given intensity was described by an exponential function and the mode intensities were not correlated with one another. The results were in good agreement with the hypothesis of the fluctuating nature of laser radiation. (AIP)

High-order multimode radiation statistics of aTEM 00 Q-switched neodymium laser

We interpret our recent experimental results concerning the dependence of the 11-photon Xe ionization rate on the axial-mode number of aQ-switched laser. If one takes the experimental procedure into account, the stochastical quantity of interest is the ratio between the instantaneous intensity and the mean intensity averaged over a round-trip duration. The enhancement factor normalized to the monomode case is the eleventh moment of that over-intensity. The measurements indicate that nearby longitudinal modes are FM-type phase correlated, while distant modes are phase independent. The radiation emitted by our Nd3+ glass laser have not the statistical properties of a pulsed Gaussian field, yet when the spectrum is sufficiently large (several Å) itsk-th-order over-intensity moment has the same valuek! as for a pulsed Gaussian field with a large spectrum.