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Results for “laser mode locking”

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.

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

High-accuracy range measurements to the moon

The lunar ranging station at the University of Texas McDonald Observatory has made more than 1800 range measurements to the four lunar retroreflectors during the first six years of its operation. Each range consists of a normal point constructed of from 5 to 20 single photoelectron returns. Normal point accuracies to about four parts in 10 to the tenth plus or minus 10 cm have become routine. The availability of excellent commercial timing equipment means that the error for such a measurement is primarily dependent on the width of the transmitted laser pulse. Second generation systems using mode-locked subnanosecond lasers can probably achieve routine normal point accuracies approaching one part in 10 to the tenth plus or minus 2 cm. High speed pockel cells may permit such accuracies to be realized with conventional Q-switched lasers.

Silverberg, E. C.↗
NASA NTRS1996

Ultrastable Multigigahertz Photonic Oscillator

Novel photonic oscillator developed to serve as ultrastable source of microwave and millimeter-wave signals. In system, oscillations generated photonically, then converted to electronic form. Includes self-mode-locked semiconductor laser producing stream of pulses, detected and fed back to laser as input. System also includes fiber-optic-delay-line discriminator, which detects fluctuations of self-mode-locking frequency and generates error signal used in negative-feedback loop to stabilize pulse-repetition frequency.

Logan, Ronald T., Jr.↗
DOE OSTI2021

Probing the ultrafast gain and refractive index dynamics of a VECSEL

Typically, strong gain saturation and gain dynamics play a crucial role in semiconductor laser mode-locking. While there have been several investigations of the ultrafast gain dynamics in vertical-external-cavity surface-emitting lasers (VECSELs), little is known about the associated refractive index changes. Yet, such refractive index changes do not only have a profound impact on the pulse formation process leading to self-phase modulation, which needs to be compensated by dispersion, but they are also of particular relevance for assessing the feasibility of Kerr-lens mode-locking of VECSELs. Here, we measure both refractive index as well as gain dynamics of a VECSEL chip using the ultrafast beam deflection method. We find that, in contrast to the gain dynamics, the refractive index dynamics is dominated by an instantaneous (100 fs) and a very slow component (100 ps). The time-resolved measurement of nonlinear refraction allows us to predict a pulse-length dependent, effective nonlinear refractive index n 2,eff , which is shown to be negative and on the order of 10 -16 m 2 =W for short pulse lengths (100 fs). It becomes positive for large excitation fluences and large pulse lengths (few ps). These results agree with some previous reports of self-mode-locked VECSELs for which the cavity design and pulse properties determine sign and strength of the nonlinear refractive index when assuming Kerr-lens mode-locking.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Integrated structured light architectures

Abstract The structural versatility of light underpins an outstanding collection of optical phenomena where both geometrical and topological states of light can dictate how matter will respond or display. Light possesses multiple degrees of freedom such as amplitude, and linear, spin angular, and orbital angular momenta, but the ability to adaptively engineer the spatio-temporal distribution of all these characteristics is primarily curtailed by technologies used to impose any desired structure to light. We demonstrate a laser architecture based on coherent beam combination offering integrated spatio-temporal field control and programmability, thereby presenting unique opportunities for generating light by design to exploit its topology.

42 ENGINEERING↗
NASA NTRS1980

Analysis of mode-locked and intracavity frequency-doubled Nd:YAG laser

The paper presents analytical and computer studies of the CW mode-locked and intracavity frequency-doubled Nd:YAG laser which provide new insight into the operation, including the detuning behavior, of this type of laser. Computer solutions show that the steady-state pulse shape for this laser is much closer to a truncated cosine than to a Gaussian; there is little spectral broadening for on-resonance operation; and the chirp is negligible. This leads to a simplified analytical model carried out entirely in the time domain, with atomic linewidth effects ignored. Simple analytical results for on-resonance pulse shape, pulse width, signal intensity, and harmonic conversion efficiency in terms of basic laser parameters are derived from this model. A simplified physical description of the detuning behavior is also developed. Agreement is found with experimental studies showing that the pulsewidth decreases as the modulation frequency is detuned off resonance; the harmonic power output initially increases and then decreases; and the pulse shape develops a sharp-edged asymmetry of opposite sense for opposite signs of detuning.

Siegman, A. E.↗
NASA NTRS1973

Gated high speed optical detector

The design, fabrication, and test of two gated, high speed optical detectors for use in high speed digital laser communication links are discussed. The optical detectors used a dynamic crossed field photomultiplier and electronics including dc bias and RF drive circuits, automatic remote synchronization circuits, automatic gain control circuits, and threshold detection circuits. The equipment is used to detect binary encoded signals from a mode locked neodynium laser.

Green, S. I.↗
NASA NTRS1979

Tunable single-longitudinal-mode operation of an injection-locked TEA CO2 laser

The tunable single-longitudinal-mode operation of a TEA CO2 laser by an injection technique using a CW waveguide laser as the master oscillator is reported. With the experimental arrangement described, in which the waveguide laser frequency is tuned to correspond to one of the oscillating longitudinal modes of the TEA laser, single-longitudinal-mode operation was achieved with no apparent reduction in the TEA output energy, on various CO2 lines with frequency offsets from the line center as large as 300 MHz. The capability of this technique for high-resolution spectroscopy or atmospheric lidar studies is demonstrated by the recording of the absorption spectrum of a strong ozone line.

Megie, G.↗
DOE OSTI2023

Spectral shaping of an ultrafast ytterbium fiber laser via a passive intracavity optical filter: a simple and reliable route to sub-45 fs pulses

We investigate the use of passive intracavity optical filters for controlling the laser output spectrum of a polarization-mode-locked, ultrafast ytterbium fiber laser. The overall lasing bandwidth is increased or extended by strategic choice of the filter cutoff frequency. Overall laser performance, including pulse compression and intensity noise, is investigated for both shortpass and longpass filters with a range of cutoff frequencies. The intracavity filter not only shapes the output spectra, but also provides a route for overall broader bandwidths and shorter pulses in ytterbium fiber lasers. These results demonstrate that spectral shaping with a passive filter is a useful tool to routinely achieve sub-45 fs pulse durations in ytterbium fiber lasers.

Cooper, Nicholas D.↗
NASA NTRS1986

Picosecond coherent anti-Stokes Raman scattering (CARS) study of vibrational dephasing of carbon disulfide and benzene in solution

The vibrational dephasing of the 656/cm mode (nu1, a1g) of CS2 and the 991/cm mode (nu2, a1g) of benzene have been studied as a function of concentration in mixtures with a number of solvents using a ps time-resolved CARS technique. This technique employs two tunable synchronously-pumped mode-locked dye lasers in a stimulated Raman pump, coherent anti-Stokes Raman probe time-resolved experiment. Results are obtained for CS2 in carbon tetrachloride, benzene, nitrobenzene, and ethanol and for benzene nu2 in CS2. The dephasing rates of CS2 nu1 increase on dilution with the polar solvents and decrease or remain constant on dilution with the nonpolar solvents. The CS2/benzene solutions show a contrasting behavior, with the CS2 nu1 dephasing rate being nearly independent of concentration whereas the benzene nu2 dephasing rate decreases on dilution. These results are compared to theoretical models for vibrational dephasing of polyatomic molecules in solution.

Perry, Joseph W.↗
DOE OSTI2024

Final Report

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70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗