104 research outputs found
An X-Ray Regenerative Amplifier Free-Electron Laser Using Diamond Pinhole MIrrors
Free-electron lasers (FELs) have been built ranging in wavelength from
long-wavelength oscillators using partial wave guiding through ultraviolet
through hard x-ray FELs that are either seeded or start from noise (SASE).
Operation in the x-ray spectrum has relied on single-pass SASE due either to
the lack of seed lasers or difficulties in the design of x-ray mirrors.
However, recent developments in the production of diamond crystal Bragg
reflectors point the way to the design of regenerative amplifiers (RAFELs)
which are, essentially, low-Q x-ray free-electron laser oscillators (XFELOs)
that out-couple a large fraction of the optical power on each pass. A RAFEL
using a six-mirror resonator providing out-coupling of 90% or more through a
pinhole in the first downstream mirror is proposed and analyzed using the
MINERVA simulation code for the undulator interaction and the Optics
Propagation Code (OPC) for the resonator. MINERVA/OPC has been used in the past
to simulate infrared FEL oscillators. For the present purpose, OPC has been
modified to treat Bragg reflection from diamond crystal mirrors. The six-mirror
resonator design has been analyzed within the context of the LCLS-II beamline
under construction at the Stanford Linear Accelerator Center and using the HXR
undulator which is also to be installed on the LCLS-II beamline. Simulations
have been run to optimize and characterize the properties of the RAFEL, and
indicate that substantial powers are possible at the fundamental (3.05 keV) and
third harmonic (9.15 keV).Comment: 9 pages, 14 figure
Using ultra-short pulses to determine particle size and density distributions
We analyze the time dependent response of strongly scattering media (SSM) to
ultra-short pulses of light. A random walk technique is used to model the
optical scattering of ultra-short pulses of light propagating through media
with random shapes and various packing densities. The pulse spreading was found
to be strongly dependent on the average particle size, particle size
distribution, and the packing fraction. We also show that the intensity as a
function of time-delay can be used to analyze the particle size distribution
and packing fraction of an optically thick sample independently of the presence
of absorption features. Finally, we propose an all new way to measure the shape
of ultra-short pulses that have propagated through a SSM.Comment: 15 pages, 29 figures, accepted for publication in Optics Express will
update with full reference when it is availabl
Surface acoustic waves for acousto-optic modulation in buried silicon nitride waveguides
We theoretically investigate the use of Rayleigh surface acoustic waves
(SAWs) for refractive index modulation in optical waveguides consisting of
amorphous dielectrics. Considering low-loss SiN waveguides with a
standard core cross section of 4.40.03 m size, buried 8 m
deep in a SiO cladding we compare surface acoustic wave generation in
various different geometries via a piezo-active, lead zirconate titanate film
placed on top of the surface and driven via an interdigitized transducer (IDT).
Using numerical solutions of the acoustic and optical wave equations, we
determine the strain distribution of the SAW under resonant excitation. From
the overlap of the acoustic strain field with the optical mode field we
calculate and maximize the attainable amplitude of index modulation in the
waveguide. For the example of a near-infrared wavelength of 840 nm, a maximum
shift in relative effective refractive index of 0.7x10 was obtained for
TE polarized light, using an IDT period of 30 - 35 m, a film thickness of
2.5 - 3.5 m, and an IDT voltage of 10 V. For these parameters, the
resonant frequency is in the range 70 - 85 MHz. The maximum shift increases to
1.2x10, with a corresponding resonant frequency of 87 MHz, when the
height of the cladding above the core is reduced to 3 m. The relative
index change is about 300-times higher than in previous work based on
non-resonant proximity piezo-actuation, and the modulation frequency is about
200-times higher. Exploiting the maximum relative index change of
1.210 in a low-loss balanced Mach-Zehnder modulator should allow
full-contrast modulation in devices as short as 120 m (half-wave voltage
length product = 0.24 Vcm).Comment: 19 pages, 8 figure
A gain-coefficient switched Alexandrite laser
We report on a gain-coefficient switched Alexandrite laser. An electro-optic
modulator is used to switch between high and low gain states by making use of
the polarization dependent gain of Alexandrite. In gain-coefficient switched
mode, the laser produces 85 ns pulses with a pulse energy of 240 mJ at a
repetition rate of 5 Hz.Comment: 8 pages, 5 figure
One-Watt level mid-IR output, singly resonant, continuous-wave optical parametric oscillator pumped by a monolithic diode laser
We report more than 1.1 Watt of idler power at 3373 nm in a singly resonant optical parametric oscillator (SRO), directly pumped by a single-frequency monolithic tapered diode laser. The SRO is based on a periodically poled MgO:LiNbO3 crystal in a four mirror cavity and is excited by 8.05 W of 1062 nm radiation. The SRO pump power at threshold is 4 W. The internal slope-efficiency and conversion efficiency reach 89% and 44% respectively. The signal and idler waves are temperature tuned in the range of 1541 to 1600 nm and 3154 to 3415 nm respectively. To the best of our knowledge, this is the highest output obtained for a diode pumped optical parametric oscillator (OPO), and the first time a SRO is directly pumped by a monolithic tapered diode laser
On-Chip Phase-Shift Induced Control of Supercontinuum Generation in a Dual-Core SiN Waveguide
We investigate on-chip spectral control of supercontinuum generation, taking
advantage of the additional spatial degree of freedom in strongly-coupled
dual-core waveguides. Using numerical integration of the multi-mode generalized
nonlinear Schr\"odinger equation, we show that, with proper waveguide
cross-section design, selective excitation of supermodes can vary the
dispersion to its extremes, i.e., all-normal or anomalous dispersion can be
selected via phase shifting in a Mach-Zehnder input circuit. The resulting
control allows to provide vastly different supercontinuum spectra with the same
waveguide circuit
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