An ultra-Narrowband Magneto-Optical Filter for Daylight Observations of the Mesospheric Potassium Layer Jonathan S. Friedman Arecibo Observatory Seminar

An ultra-Narrowband Magneto-Optical Filter

for Daylight Observations of the

Mesospheric Potassium Layer

An ultra-Narrowband Magneto-Optical Filter

for Daylight Observations of the

Mesospheric Potassium Layer

Jonathan S. FriedmanArecibo Observatory Seminar

9 August 2007

Jonathan S. FriedmanArecibo Observatory Seminar

9 August 2007

Arecibo Observatory, 9 August 2007


The solar spectrum near the K D-lines is heavily populated with O2 rotational absorption lines. In fact, the D2 line in potassium overlaps one such line.

The solar spectrum near the K D-lines is heavily populated with O2 rotational absorption lines. In fact, the D2 line in potassium overlaps one such line.

Potassium has coronal absorption bands, i.e. Fraunhofer lines. The D1 Fraunhofer absorption is shown at right.

Potassium has coronal absorption bands, i.e. Fraunhofer lines. The D1 Fraunhofer absorption is shown at right.

Spectral FilteringSpectral Filtering


• There are a variety of methods of spectral filtering. Color filters, spectrometers/monochrometers, interference filters and etalons are the most common.

• These suffer from low line-center throughput, broad bandwidth, poor spectral discrimination, and/or high cost. Etalons are the only technology that can work in daylight. • Etalons suffer from high cost + stability problems, especially when multiple etalons are required.

Advantages of the Faraday Anomalous Advantages of the Faraday Anomalous Dispersion Optical FilterDispersion Optical Filter

Advantages of the Faraday Anomalous Advantages of the Faraday Anomalous Dispersion Optical FilterDispersion Optical Filter


• Adjustable-width, ultra-narrowband optical filtering.

• Flat-topped filter

• No wavelength drift

•Low cost ($20K) vs. multiple etalons (>$50K)

What is a Faraday Filter? (AKA Magneto-What is a Faraday Filter? (AKA Magneto-Optical Filter or FADOF)Optical Filter or FADOF)

What is a Faraday Filter? (AKA Magneto-What is a Faraday Filter? (AKA Magneto-Optical Filter or FADOF)Optical Filter or FADOF)

The Faraday filter uses an atomic vapor cell in an axial magnetic field to rotate the polarization of light that is resonant with an electronic transition of the atomic species that makes up the vapor.

The cell and B-field are sandwiched between crossed polarizers, so light that is not resonant, and passes unimpeded through the cell does not have its polarization rotated and is extinguished.



Physical Principles (continued)Modeling the Faraday Filter

Physical Principles (continued)Modeling the Faraday Filter


QuickTime™ and aVideo decompressor

are needed to see this picture.

The AO FADOF and its spectral effectThe AO FADOF and its spectral effect


A FADOF can also be used for Rayleigh Wind Lidar


The Arecibo FADOF DesignThe Arecibo FADOF Design


Performance Tests (for 1 channel)


Performance Tests (for 2 channels)

K FADOF performance at Tenerife (28°N, 16.5° W)

K FADOF performance at Tenerife (28°N, 16.5° W)


SummarySummary

Understanding of the MLT region requires round-the-clock observations of state variables.

The solar background is obviously a huge problem for optical observations.

There are not many useful technologies, and most are costly and unwieldy.

The FADOF resolves many issues, providing a useful, economical, efficient and stable means of reducing the solar background with high line-center throughput.

Understanding of the MLT region requires round-the-clock observations of state variables.

The solar background is obviously a huge problem for optical observations.

There are not many useful technologies, and most are costly and unwieldy.

The FADOF resolves many issues, providing a useful, economical, efficient and stable means of reducing the solar background with high line-center throughput.


Extra Slides

K Energy Level DiagramK Energy Level Diagram

Filter curve for 2-pass Version

Normalized Normalized transmissions of transmissions of emissions due to emissions due to the three laser the three laser wavelengths:wavelengths:0.98440.98440.98440.98440.98450.9845

Documents

An ultra-Narrowband Magneto-Optical Filter for Daylight Observations of the Mesospheric Potassium Layer Jonathan S. Friedman Arecibo Observatory Seminar