14 research outputs found
On fundamental diffraction limitation of finesse of a Fabry-Perot cavity
We perform a theoretical study of finesse limitations of a Fabry-Perot (FP)
cavity occurring due to finite size, asymmetry, as well as imperfections of the
cavity mirrors. A method of numerical simulations of the eigenvalue problem
applicable for both the fundamental and high order cavity modes is suggested.
Using this technique we find spatial profile of the modes and their round-trip
diffraction loss. The results of the numerical simulations and analytical
calculations are nearly identical when we consider a conventional FP cavity.
The proposed numerical technique has much broader applicability range and is
valid for any FP cavity with arbitrary non-spherical mirrors which have
cylindrical symmetry but disturbed in an asymmetric way, for example, by tilt
or roughness of their mirrors.Comment: 15 pages, 10 figure
Optical Gravitational Wave Antenna with Increased Power Handling Capability
Fundamental sensitivity of an optical interferometric gravitational wave
detector increases with increase of the optical power which, in turn, limited
because of the opto-mechanical parametric instabilities of the interferometer.
We propose to optimize geometrical shape of the mirrors of the detector to
reduce the diffraction-limited finesse of unessential optical modes of the
interferometer resulting in increase of the threshold of the opto-mechanical
instabilities and subsequent increase of the measurement sensitivity. Utilizing
parameters of the LIGO interferometer we found that the proposed technique
allows constructing a Fabry-Perot interferometer with round trip diffraction
loss of the fundamental mode not exceeding ~ppm, whereas the loss of the
first dipole as well as the other high order modes exceed ~ppm and
~ppm, respectively. The optimization comes at the price of tighter
tolerances on the mirror tilt stability, but does not result in a significant
modification of the optical beam profile and does not require changes in the
the gravity detector read-out system. The cavity with proposed mirrors is also
stable with respect to the slight modification of the mirror shape.Comment: 5 pages, 4 figure
Diffraction losses of a Fabry-Perot cavity with nonidentical non-spherical mirrors
Optical cavities, with both optimized resonant conditions and high quality factors, are important metrological tools. In particular, they are used for laser gravitational wave (GW) detectors. In order to have high cavity powers in GW detectors, it is necessary to suppress the parametric instability and to reduce the loss in the arm caused by point absorbers by damping the resonant conditions of harmful higher order optical modes (HOOM). This can be achieved effectively by using non spherical mirrors in symmetric Fabry–Perot (FP) cavities by increasing roundtrip losses of HOOMs Ferdous F et al 2014 Phys. Rev. A 90 033826; Matsko A et al 2016 Phys. Rev. D 93 083010. FP cavities in most of the GW detectors have non-identical mirrors to optimize clipping losses and reduce thermal noise by reducing the beam size on one side of the cavity facing to the beam splitter and recycling cavities. We present here a general method to design non spherical non-identical mirrors in non-symmetric FP cavities to damp HOOMs. The proposed design allows us to suppress the loss of the arm power caused by point absorbers on test masses
Diffraction losses of a Fabry-Perot cavity with nonidentical non-spherical mirrors
Optical cavities with both optimized resonant conditions and high quality
factors are important metrological tools. In particular, they are used for
laser gravitational wave (GW) detectors. It is necessary to suppress the
parametric instability by damping the resonant conditions of harmful higher
order optical modes (HOOM) in order to have high cavity powers in GW detectors.
This can be achieved effectively by using non spherical mirrors in symmetric
Fabry-Perot (FP) cavities by increasing roundtrip losses of HOOMs. Fabry-Perot
cavities in most of the GW detectors have non-identical mirrors to optimize
clipping losses and reduce thermal noise by reducing the beam size on one side
of the cavity facing to the beam splitter and recycling cavities. We here
present a general method to design non spherical non-identical mirrors in
non-symmetric FP cavities to damp HOOMs. The proposed design allows to the
suppress the loss of the arm power caused by point absorbers on test masses.Comment: 12 pages, 10 figure
The noise in gravitational-wave detectors and other classical-force measurements is not influenced by test-mass quantization
It is shown that photon shot noise and radiation-pressure back-action noise
are the sole forms of quantum noise in interferometric gravitational wave
detectors that operate near or below the standard quantum limit, if one filters
the interferometer output appropriately. No additional noise arises from the
test masses' initial quantum state or from reduction of the test-mass state due
to measurement of the interferometer output or from the uncertainty principle
associated with the test-mass state. Two features of interferometers are
central to these conclusions: (i) The interferometer output (the photon number
flux N(t) entering the final photodetector) commutes with itself at different
times in the Heisenberg Picture, [N(t), N(t')] = 0, and thus can be regarded as
classical. (ii) This number flux is linear in the test-mass initial position
and momentum operators x_o and p_o, and those operators influence the measured
photon flux N(t) in manners that can easily be removed by filtering -- e.g., in
most interferometers, by discarding data near the test masses' 1 Hz swinging
freqency. The test-mass operators x_o and p_o contained in the unfiltered
output N(t) make a nonzero contribution to the commutator [N(t), N(t')]. That
contribution is cancelled by a nonzero commutation of the photon shot noise and
radiation-pressure noise, which also are contained in N(t). This cancellation
of commutators is responsible for the fact that it is possible to derive an
interferometer's standard quantum limit from test-mass considerations, and
independently from photon-noise considerations. These conclusions are true for
a far wider class of measurements than just gravitational-wave interferometers.
To elucidate them, this paper presents a series of idealized thought
experiments that are free from the complexities of real measuring systems.Comment: Submitted to Physical Review D; Revtex, no figures, prints to 14
pages. Second Revision 1 December 2002: minor rewording for clarity,
especially in Sec. II.B.3; new footnote 3 and passages before Eq. (2.35) and
at end of Sec. III.B.
Polymerization of Hexene-1 and Propylene over Supported Titanium–Magnesium Catalyst: Comparative Data on the Polymerization Kinetics and Molecular Weight Characteristics of Polymers
Data are presented on the great differences of the kinetics of hexene-1 and propylene polymerization over the same supported titanium–magnesium catalyst, as well as molecular weight and molecular weight distribution of the polymers produced. It is found that the composition of cocatalysts (AlEt3 or Al(i-Bu)3 greatly affects the kinetics of hexene-1 polymerization and molecular weight distribution of polyhexene, contrary to data obtained at propylene polymerization. The presence of hydrogen at hexene-1 polymerization leads to a much higher increase of activity in comparison with propylene polymerization. Possible reasons for these differences are discussed on the basis of experimental results
Particular issues associated with underwater low density polyethylene pelletizing in tubular reactor processes
The urgency of the discussed issue is caused by the periodic underwater pelletizing unit performance degradation in the form of spontaneous increase of number of polyethylene pellets stuck together as well as practical non*controllability of this phenomenon. The main aim of the study: definition of polyethylene fractions in both high and low pressure recycling systems being able by physical and chemical properties to initiate pellet sticking process and determination of the structure of these polymers for predicting synthesis conditions for the purpose of the further minimization. The methods used in the study: IR-Fourier and NMR 13С-spectroscopy, differential scanning calorimetry, X-ray phase analysis, selective extraction, flotation density determination. The results: based on the data of physical and chemical polyethylene deposit analysis in high pressure systems the authors have made an assumption that the reason of pellet sticking is uncontrolled penetration of the polymer with such characteristics into the melt. Mixing of amorphized polymer deposit with low melting and crystallization temperatures with polyethylene of basic grade 153 was simulated; the comparison with stuck together pellets material in a contact point was made. Using the differential scanning calorimetry and X-ray phase analysis methods the material characteristic similarity was demonstrated
Ethylene Polymerization over Supported Vanadium-Magnesium Catalysts with Different Vanadium Content: The Effect of Hydrogen on Molecular Weight Characteristics of the Produced Bimodal Polyethylene
Data are presented on the activity of supported vanadium-magnesium catalysts (VMCs) with different vanadium content in ethylene polymerization and the molecular weight characteristics of the produced polyethylene. The VC1 catalyst, with a very low vanadium content (0.12 wt.%), showed a sixfold higher activity per unit weight of vanadium than the VC2 catalyst with a high-vanadium content (4.0 wt.%). Additionally, the total activity of VC2 (kg PE/g cat·h) was fivefold higher when compared to VC1. The introduction of hydrogen in polymerization leads to a considerable decrease in the activity of both catalysts. The polyethylene obtained in the presence of hydrogen over both catalysts has a broad bimodal molecular weight distribution (MWD) with a distinct shoulder in the high-molecular region (Mw ≥ 106 g/mol). Decomposition of the MWD curves of bimodal polyethylene into two fractions (high- and low-molecular fractions) made it possible to determine for the first time the ratio of the reaction rate constants of chain transfer with hydrogen (KtrH) and polymer chain propagation (Kp) for two groups of the VMC active sites producing low- and high-molecular fractions of bimodal polyethylene