A new method for performing an absolute measurement of the geomagnetic field

Recent developments in next generation disc technology, cameras in mobile phones, zoom-lenses for small digital cameras and camcorders, digital SLRs, and television cameras have amplified the demand for affordable optical systems with outstanding image quality, a combination that can only be achieved using aspheric surfaces. The metrology of aspheric surfaces is a classical problem, but solutions so far have not fulfilled all demands for system cost, TACT (Total Average Cycle Time), minimized tooling, measurement uncertainty, spatial resolution, robustness in a production environment and many more. Zygo Corp. presents here a new method [1,2] for measurement of rotationally symmetrical aspheric surfaces using a new commercial system, which has the potential to fulfill these industry requirements. During measurement, the surface is scanned along its symmetry axis in a Fizeau cavity with a spherical reference surface. The coordinates x,y,z at the (moving) zone of normal incidence are derived from simultaneous phase-measurements at the apex and zone. Phase-shifting Fizeau interferometry and displacement interferometry are combined in the new commercial system to realize this new method. Aspheric departure from a best-fitsphere approaching 800 microns can be measured, and absolute measurement is possible with an absolutely calibrated transmission sphere. A custom parabolic artifact is measured with conventional null Fizeau interferometry and by the new commercial system. Data is reported for each technique along with a difference map achieved by fiducialized data subtract where 32.0 nm peak-to-valley (PV) and 3.6 nm R.M.S. are achieved.

Download Full-text

A new method for the absolute measurement of electric quantity

Bulletin of the Bureau of Standards ◽

10.6028/bulletin.151 ◽

1910 ◽

Vol 6 (4) ◽

pp. 503

Author(s):

B. McCullom

Keyword(s):

Absolute Measurement ◽

New Method ◽

The Absolute ◽

Electric Quantity

Download Full-text

A new method for the absolute measurement of reflectivity

Mineralogical Magazine and Journal of the Mineralogical Society ◽

10.1180/minmag.1966.035.274.07 ◽

1966 ◽

Vol 35 (274) ◽

pp. 861-866 ◽

Cited By ~ 3

Author(s):

P. M. D. Bradshaw ◽

R. Phillips ◽

R. A. Smith

Keyword(s):

Light Beam ◽

Normal Incidence ◽

Absolute Measurement ◽

New Method ◽

Spectral Reflectivity ◽

The Absolute

SummaryThe theory of a new method for the determination of reflectivity at truly normal incidence is described. A parallel light beam falls on the specimen after passing through a glass cube with semi-silvered diagonal mounted at the centre of an optical goniometer. The various reflected beams are measured by a photomultiplier fixed to the telescope of the goniometer. Experiment has proved the validity of the method and the spectral reflectivity of pyrite in air and in oil has been investigated.

Download Full-text

Sequicentenary of Gauss's first measurement of the absolute value of magnetic intensity

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1982.0060 ◽

1982 ◽

Vol 306 (1492) ◽

pp. 5-8 ◽

Cited By ~ 11

Keyword(s):

Geomagnetic Field ◽

Absolute Measurement ◽

Spherical Harmonic Analysis ◽

Magnetic Intensity ◽

Universal System ◽

Deep Interior ◽

System Of Units ◽

Worldwide Network ◽

Physical Quantities ◽

Magnetic Observatories

The geomagnetic field and its changes with time are major tools for probing the Earth’s deep interior. It is therefore particularly appropriate that the Royal Society Discussion Meeting on the Earth’s core should coincide with the 150th anniversary of the first absolute measurement of the intensity of the geomagnetic field. This was only one of Carl Friedrich Gauss’s many contributions, both direct and indirect, to geomagnetism. For example, it was Gauss who devised the methods of least squares and of spherical harmonic analysis. With Weber, he applied these to the geomagnetic field to show that it was nearly all of internal origin. Gauss was also the initiator of, and an active participant in, the ‘Gottingen Magnetic Union’, a scheme for the simultaneous observation of the magnetic field at widespread sites from which has developed the present worldwide network of magnetic observatories. The particular achievement that we commemorate here was the determination by Gauss of the horizontal intensity of the geomagnetic field in units related to the millimetre, milligram and second. (This was one tenth of the unit that subsequently bore his name.) At that time he was working towards a universal system of units for all physical quantities and conceived the original idea that magnetic intensity can be measured in terms of mass, length and time.

Download Full-text

COMPARATIVE TEST OF TWO METHODS OF QUANTUM EFFICIENCY ABSOLUTE MEASUREMENT BASED ON SQUEEZED VACUUM DIRECT DETECTION

International Journal of Quantum Information ◽

10.1142/s0219749911007265 ◽

2011 ◽

Vol 09 (supp01) ◽

pp. 251-262 ◽

Cited By ~ 3

Author(s):

I. N. AGAFONOV ◽

M. V. CHEKHOVA ◽

A. N. PENIN ◽

G. O. RYTIKOV ◽

O. A. SHUMILKINA ◽

...

Keyword(s):

Quantum Efficiency ◽

Direct Detection ◽

Photon Counting ◽

Absolute Measurement ◽

High Gain ◽

New Method ◽

Absolute Calibration ◽

Squeezed Vacuum ◽

The Difference ◽

Absolute Quantum

We realize and test in experiment a method recently proposed for measuring absolute quantum efficiency of analog photodetectors. Similar to the traditional (Klyshko) method of absolute calibration, the new one is based on the direct detection of two-mode squeezed vacuum at the output of a traveling wave OPA. However, in the new method, one measures the difference-photocurrent variance rather than the correlation function of photocurrents (number of coincidences), which makes the technique applicable for high-gain OPA. In this work we test the new method versus the traditional one for the case of photon-counting detectors where both techniques are valid.

Download Full-text

Study of the Correction Method of Secular Variation in the Main Geomagnetic Field by the Field Seismogeomagnetic Survey

10.21203/rs.3.rs-742920/v1 ◽

2021 ◽

Author(s):

shupeng su ◽

ZhaoJing Wang ◽

Deqiang Liu ◽

Fenglong Mao

Keyword(s):

Magnetic Field ◽

Secular Variation ◽

Geomagnetic Field ◽

Least Squares Method ◽

Weighted Least Squares ◽

Correction Method ◽

Original Method ◽

New Method ◽

Field Variation ◽

The Mean

Abstract The correction of the secular variation (SV) of the main geomagnetic field is a key link of field seismogeomagnetic data processing, and the current method relies on the observatory data for the relevant technical processing. To optimize the data products and obtain more accurate and reliable seismomagnetic information, this study adopted a new technical idea, which uses the repeated survey data from field stations to obtain the SV of the main geomagnetic field over the survey area by the weighted least-squares method, and compared the results with those of the current methods. The results were as follows: 1. The SV results of the main geomagnetic field produced by the new method are closer to those of the International Geomagnetic Reference Field (IGRF)_SV model. The mean square error (MSE) of the difference of the three elements F, D, and I between the new method and the IGRF_SV model is 10.7%, 47.0%, and 14.5% of that of the original method, respectively. 2. By applying the new SV correction method, more stable and reasonable variations in Earth’s crustal magnetic field can be obtained. The average amplitude of the Earth’s crustal magnetic field variation in the three elements F, D, and I is 28.5%, 55.4%, and 34.4 of the original results, the MSE is 59.1%, 56.5%, and 40.3% of the original results, and the mean gradient is 93.6%, 91.9%, and 97.0%, respectively. 3. In the processed results of the new method, the seismomagnetic information is clearly optimized, and the location of the epicenter is more consistent with the 0 value line of the Earth’s crustal magnetic field. The processed results of the new method are significantly better than those of the original method and have a higher application value.

Download Full-text