Search NASA⌕ Search

SEARCH · Search NASA

Results for “laser methods”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Length controlled stabilized mode-lock ND:YAG laser

A method and apparatus for stabilizing the amplitude and repetition rate of mode-locked Nd:YAG laser pulses by controlling the laser length through a feedback loop are described. The end mirror of the laser is mounted on a piezoelectric crystal which is dithered at a low frequency. A portion of fundamental 1.06 micrometer laser radiation is converted into its second harmonic frequency, and the average power of the second harmonic frequency is detected by an integrating detector. The amount of the power of the second harmonic frequency depends on the match between the optical length of the laser cavity and the mode-lock frequency. The length is controlled by a feedback loop which phase compares the output of the second harmonic detector to the piezoelectric crystal dither signal.

Sigfred, J.↗
NASA NTRS1989

Method and circuit for shaping laser output pulses

The invention is a method and circuit for shaping laser output pulses from a laser resonator. A Q-switch and polarizer act in combination to control the loss to the resonator and provide the laser output representative of such loss. An optical diode senses the level of the output pulse and provides an output signal that when amplified is used to control voltage from a supply to provide a control signal which is applied to the Q-switch to control the shape of the output pulse by adjusting its length.

Barnes, Norman P.↗
NASA NTRS1990

Method and circuit for shaping laser output pulses

The invention is a method and circuit for shaping laser pulses 17' in which a laser medium 12' in a laser resonator 10' that includes a Q-switch 14' and polarizer 13' which act in combination to control the loss of the resonator 10' and provide the laser output 17' representative of such loss. An optical diode 22' senses the level of the output pulse 17' and provides an output signal 23' that when amplified is used with a control voltage from a supply 29' provide a control signal 19' which is applied to Q-switch 14' to control the shape of the output pulse 17' by adjusting its length.

Barnes, Norman P.↗
NASA NTRS1987

Method and apparatus for enhancing laser absorption sensitivity

A simple optomechanical method and apparatus is described for substantially reducing the amplitude of unwanted multiple interference fringes which often limit the sensitivities of tunable laser absorption spectrometers. An exterior cavity is defined by partially transmissible surfaces such as a laser exit plate, a detector input, etc. That cavity is spoiled by placing an oscillating plate in the laser beam. For tunable diode laser spectroscopy in the mid-infrared region, a Brewster-plate spoiler allows the harmonic detection of absorptances of less than 10 to the -5 in a single laser scan. Improved operation is achieved without subtraction techniques, without complex laser frequency modulation, and without distortion of the molecular lineshape signal. The technique is applicable to tunable lasers operating from UV to IR wavelengths and in spectrometers which employ either short or long pathlengths, including the use of retroreflectors or multipass cells.

Webster, Christopher R.↗
NASA NTRS1984

Reverse laser drilling

This invention provides a method for laser drilling small diameter, closely-spaced, and accurately located holes in a body of material which is transparent or substantially transparent to the laser radiation employed whereby the holes are drilled through the thickness of the body from the surface opposite to that on which the laser beam impinges to the surface of laser beam impingement.

Anthony, Thomas R.↗
NASA NTRS1990

Canopy architecture measured with a laser

A laser based method was employed to measure and numerically describe the architecture of a corn canopy. Use of the method provides an interception coefficient for classes of vegetation in layers of the canopy viewed in various directions. Architectural data obtained for similar corn canopies but measured by differing methods are comparable to the results obtained using the laser based method. These results provide input data to mathematical models employed in remote sensing for describing the radiation environment in a plant canopy and predicting its reflectance.

Vanderbilt, Vern C.↗
NASA NTRS1986

Laser sounding of instantaneous and mean speed of wind using correlation method

The correlation methods for laser sounding of wind speed are based on mutual processing of lidar signals scattered from several spatially separated volumes at each altitude investigated. The time of atmospheric aerosol transport between the scattering volumes estimated by the position of maximum of the mutual correlation function is the measure of corresponding wind speed. In this case the distance between the scattering volumes (the measuring base), defining the time of aerosol movement through the measuring base also determines the lidar possibilities for measuring the instantaneous (during the time interval of several seconds) or the mean wind speed (some minutes). Based on the experimental investigations performed using two lidars, these possibilites are analyzed.

Zuev, V. E.↗
NASA NTRS1981

Processing of silicon solar cells by ion implantation and laser annealing

Methods to improve the radiation tolerance of silicon cells for spacecraft use are described. The major emphasis of the program was to reduce the process-induced carbon and oxygen impurities in the junction and base regions of the solar cell, and to measure the effect of reduced impurity levels on the radiation tolerance of cells. Substrates of 0.1, 1.0 and 10.0 ohm-cm float-zone material were used as starting material in the process sequence. High-dose, low-energy ion implantation was used to form the junction in n+p structures. Implant annealing was performed by conventional furnace techniques and by pulsed laser and pulsed electron beam annealing. Cells were tested for radiation tolerance at Spire and NASA-LeRC. After irradiation by 1 MeV electrons to a fluence of 10 to the 16th power per sq cm, the cells tested at Spire showed no significant process induced variations in radiation tolerance. However, for cells tested at Lewis to a fluence of 10 to the 15th power per sq cm, ion-implanted cells annealed in vacuum by pulsed electron beam consistently showed the best radiation tolerance for all cell resistivities.

Minnucci, J. A.↗
NASA NTRS1984

Analysis and testing of a new method for drop size measurement using laser scatter interferometry

Research was conducted on a laser light scatter detection method for measuring the size and velocity of spherical particles. The method is based upon the measurement of the interference fringe pattern produced by spheres passing through the intersection of two laser beams. A theoretical analysis of the method was carried out using the geometrical optics theory. Experimental verification of the theory was obtained by using monodisperse droplet streams. Several optical configurations were tested to identify all of the parametric effects upon the size measurements. Both off-axis forward and backscatter light detection were utilized. Simulated spray environments and fuel spray nozzles were used in the evaluation of the method. The measurements of the monodisperse drops showed complete agreement with the theoretical predictions. The method was demonstrated to be independent of the beam intensity and extinction resulting from the surrounding drops. Signal processing concepts were considered and a method was selected for development.

Bachalo, W. D.↗
NASA NTRS1998

Method and Apparatus for Linewidth Reduction in Distributed Feedback or Distributed Bragg Reflector Semiconductor Lasers using Vertical Emission

The linewidth of a distributed feedback semiconductor laser or a distributed Bragg reflector laser having one or more second order gratings is reduced by using an external cavity to couple the vertical emission back into the laser. This method and device prevent disturbance of the main laser beam. provide unobstructed access to laser emission for the formation of the external cavity. and do not require a very narrow heat sink. Any distributed Bragg reflector semiconductor laser or distributed feedback semiconductor laser that can produce a vertical emission through the epitaxial material and through a window in the top metallization can be used. The external cavity can be formed with an optical fiber or with a lens and a mirror of grating.

Cook, Anthony L.↗
NASA NTRS2018

Index-Coupled Distributed-Feedback Semiconductor Quantum Cascade Lasers Fabricated Without Epitaxial Regrowth

Quantum cascade (QC) lasers and methods of fabricating such QC lasers are provided. The QC lasers incorporate a DFB grating without requiring the use of relying on epitaxial regrowth processes. The DFB gratings are formed as sidewall gratings along the lateral length of the QC active region, or the DFB gratings are formed atop the lateral length of the QC active region, and wherein the top DFB grating is planarized with a polymeric material.

Briggs, Ryan M.↗
NASA NTRS2003

Laser Synthesis of Supported Catalysts for Carbon Nanotubes

Four methods of laser assisted catalyst generation for carbon nanotube (CNT) synthesis have been tested. These include pulsed laser transfer (PLT), photolytic deposition (PLD), photothermal deposition (PTD) and laser ablation deposition (LABD). Results from each method are compared based on CNT yield, morphology and structure. Under the conditions tested, the PLT was the easiest method to implement, required the least time and also yielded the best pattemation. The photolytic and photothermal methods required organometallics, extended processing time and partial vacuums. The latter two requirements also held for the ablation deposition approach. In addition to control of the substrate position, controlled deposition duration was necessary to achieve an active catalyst layer. Although all methods were tested on both metal and quartz substrates, only the quartz substrates proved to be inactive towards the deposited catalyst particles.

VanderWal, Randall L.↗
NASA NTRS1982

A proposed new method for damping relaxation oscillations in laser diodes

A new concept of damping relaxation oscillations in injection laser diodes is described. This method involves the operation of the laser as a part of a bipolar transistor, and the damping is accomplished by reducing the carrier lifetime in the laser active region only at frequencies near resonance. The advantage of the proposed method is that the damping mechanism does not affect the laser operation at any other frequency range.

Katz, J.↗
NASA NTRS2015

Apparatus and Method to Enable Precision and Fast Laser Frequency Tuning

An apparatus and method is provided to enable precision and fast laser frequency tuning. For instance, a fast tunable slave laser may be dynamically offset-locked to a reference laser line using an optical phase-locked loop. The slave laser is heterodyned against a reference laser line to generate a beatnote that is subsequently frequency divided. The phase difference between the divided beatnote and a reference signal may be detected to generate an error signal proportional to the phase difference. The error signal is converted into appropriate feedback signals to phase lock the divided beatnote to the reference signal. The slave laser frequency target may be rapidly changed based on a combination of a dynamically changing frequency of the reference signal, the frequency dividing factor, and an effective polarity of the error signal. Feed-forward signals may be generated to accelerate the slave laser frequency switching through laser tuning ports.

Chen, Jeffrey R.↗
NASA NTRS1999

In situ Diagnostics During Carbon Nanotube Production by Laser Ablation

The preliminary results of spectral analysis of the reaction zone during the carbon nanotube production by laser ablation method indicate synergetic dependence on dual laser setup. The emission spectra recorded from different regions of the laser ablated plume at different delay times from the laser pulses are used to map the temperatures of C2 and C3. These are compared with Laser Induced Fluorescence (LIF) spectra also obtained during production to model the growth mechanism of carbon nanotubes. Experiments conducted to correlate the spectral features with nanotube yields as a function of different production parameters will be discussed.

Arepalli, Sivaram↗
NASA NTRS2019

Laser Light Sheet Flow Visualization of the Space Launch System Booster Separation Test

Planar flow visualizations were obtained in a wind tunnel test in the NASA Langley Research Center’s Unitary Plan Wind Tunnel using the laser-light-sheet method. This method uses a laser to illuminate fine particles generated in the wind tunnel to visualize flow structures. The test article was designed to simulate the separation of the two solid rocket boosters (SRBs) from the core stage of the NASA Space Launch System (SLS) at Mach 4 using a scale model. The test was run on of the SLS Block 1B Cargo (27005) configuration and the SLS Block 1B Crew (28005) configuration. Planar flow visualization was obtained only on the crew configuration. Air at pressures up to 1500 psi was used to simulate plumes from the booster separation motors (BSMs) located at the nose, and aft skirt of the two boosters. The facility free stream was seeded with water vapor, which condensed and froze into small ice crystals in the tunnel nozzle expansion. A continuous wave green (532 nm) laser sheet was used to illuminate the ice crystals, and the resulting Mie-scattered light was collected with a camera. The resulting images clearly identify shock waves and other flow features including BSM plume shapes. Measurements were acquired for different BSM pressures and booster separation locations.

Danehy, Paul M.↗
NASA NTRSDate not supplied

Ultrashort Pulsed Laser Treatment: A Novel Sterilization Method for Planetary Protection

Introduction: On missions seeking signs of potential life elsewhere in the solar system, we have an obligation not to bring our own Earthly life with us. Reducing the bioburden (number of living microbes) on spacecraft is therefore required by the COSPAR Policy on Planetary Protection to target bodies that are of interest for understanding the origins of life (such as Mars). The method of spacecraft sterilization predominantly used by NASA is Heat Microbial Reduction, which is typically incompatible with heat-sensitive components such as optics and electronics, and is expensive and time-consuming. Here, we present preliminary results on a novel method for spacecraft hardware sterilization: high-intensity ultrashort (femtosecond) pulsed laser illumination. Femtosecond lasers use extremely high photon fluxes (10^29 photons/sec*cm^2, ~0.03 J/cm^2) in extremely short pulses, which can inactivate even stress-tolerant microbial spores with minimal damage to the spacecraft surface. This rapid sterilization technique could be carried out in situ in a spacecraft assembly clean room using high-speed surface scanning, saving critical time and resources. It also can potentially remove or reduce debris from inactivated cells and spores. Methods: To develop optimal laser processing parameters for inactivating planetary protection-relevant organisms on metal surfaces, we inoculated 1-cm^2 mirror-polished aluminum coupons with Bacillus subtilis spores (2x10^5 spores/coupon) and tested the effect of several parameters, including pulse count and fluence. Sterilization effectiveness was measured by recovering spores using a PVA (polyvinyl acetate) peel and conducting serial dilution and plating for colony-forming units (CFUs). Results: Our results show that pulse count and fluence both affect sterilization effectiveness and that within a certain pulse count range, increasing fluence increases effectiveness. We have demonstrated the ability to reduce viable microbial counts by at least 10^-4. Future work will include testing higher abundances and different species of microorganisms, effectiveness on complex surfaces, compatibility with sensitive surfaces, and quantification of cell debris removal. Femtosecond pulsed laser illumination has the potential to provide dramatic savings in both cost and schedule over current methods of bioburden reduction to prevent forward contamination. It may also have the potential for use in surface sterilization of returned samples to prevent back contamination.

Planetary Protection; Lasers; Sterilization; Bacil↗