Let there be light! Fiat lux!

Edge of the envelope

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Schumann-Runge Oxygen absorption bands

This figure represents data collected with a deuterium lamp, McPherson Model 2035 monochromator, 1800g/mm grating and CCD detector. No special preparation is required and the figure shows absorbance of atmospheric gases inside the monochromator, partly resolved Schumann-Runge band spectrum. This is Oxygen absorption in the ultraviolet - at the edge of atmospheric gases transparency. Spectral resolution is not adequate to resolve rotational structure. Never less the ad hoc spectrum illustrates absorbance at the very "edge of the envelope.” This spectrum can provide means to calibrate ultraviolet spectrometer systems wavelength in-situ. Spectroscopy at “vacuum ultraviolet” (VUV) wavelengths are nominally below 185 nanometers and require removal of atmospheric oxygen and water vapor. Usually this is accomplished by building the instrument in a housing that can be evacuated all ambient gases removed to high-vacuum e.g. 10E-6 mbar (monochromators are available for vacuum range VUV and shorter wavelengths)

Lyman-Alpha with 234302

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lyman-alpha emission line from deuterium lamp, low resolution

This emission line is from a deuterium lamp and is one way to check resolution; test for 121 nanometers with 10um slit width X 4mm high ... dispersion in the 234/302 varies a little bit with wavelength. What wavelength is used to set specification 30.4, 121.6, 184.9 nm, etc. We test and demonstrate spectral-resolution with every instrument that we ship. Every time. We meet the specification on data sheet every time. The masterpiece aberration corrected grating substrate is 45*40mm size. We calculate f/no by the equivalent circular Area of the grating. How do you do it?

World-Class Infrared Calibration

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The National Institute of Standards and Technology (NIST) Optical Radiation Group made an announcement about one year ago about the "A New, World-Class Facility for Infrared Calibrations".

"This is a major achievement that will allow measurements in the difficult infrared to far-infrared part of the spectrum to approach the accuracy now possible in the visible and ultraviolet spectrum where high-quality standard detectors have been available for years," says Gerald Fraser, Chief of NIST's Sensor Science Division. "The effort will allow R&D teams to better leverage the capabilities of the infrared spectrum for applications that range from infrared astronomy to quality control in manufacturing."

Spectrometer for Infrared Calibrations

Calibration setup: (A) infrared source, (B) monochromator, (C) output beam and device under test (red) next to NIST standard detector

Across the pond, in the United Kingdom the National Physics Lab has a nice optical metrology offering too. NPL's optical radiation scientists provide a wide range of measurements for characterising sources and detectors and the properties of materials, covering the ultraviolet, visible and infrared regions.

Infrared Reflectance Standards from NPL cover the spectral range 2.5 µm to 55.6 µm (4000 - 180 cm-1) is carried out with special optical devices mounted in the large sample compartments. These devices consist of a regular reflectance accessory or a variable angle regular reflectometer or a hemispherical reflectometer / transmissometer devised at NPL[1]. The regular reflectometer[5] can be used validly only for measurements on optically flat polished surfaces that have no diffuse component of reflection, and the angle of incidence is 10°. The variable angle reflectometer[5] can also only be used for optically flat non-scattering surfaces, and the angle of incidence may be anything from 20° to 85°. Rigorous control of polarisation is necessary in this case.

[1] CLARKE, F.J.J. Measurement of the radiometric properties of materials for building and aerospace applications. Proc. Soc. Photo-Opt. Instrum. Eng. 1980, 234, 40-47

[5]CLARKE, F.J.J. Infrared regular reflectance standards from NPL. Proc. Soc. Photo-Opt. Instrum. Eng. 1996, 2776, 184-195

Czerny-Turner Design redux

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From the Journal of the Optical Society of America and by our friend Joseph Reader, the paper "Optimizing Czerny–Turner Spectrographs: A Comparison between Analytic Theory and Ray Tracing" in that the analytic theory of aberrations has been used to derive an expression for the magnitude of the coma width of the image in the meridional plane in a Czerny–Turner spectrograph with unequal mirror radii. The calculated properties of a 4-m spectrograph with equal radii and a recently constructed 3.34-m spectrograph with unequal radii are compared with the results obtained by tracing individual rays. The agreement is excellent, in contrast to the results of Chandler [ J. Opt. Soc. Am. 58, 895 ( 1968)]. The lateral position of the grating for complete elimination of coma found experimentally with the 3.34-m instrument is in fair agreement with the theory. A correction to the 3̅√ longitudinal grating position is given for a Czerny–Turner spectrograph which results in a flatter focal surface. ©1969 Optical Society of America

the Czerny-Turner design as shown in the Appendix of Reader's paper

EUV laser spectrometers

Excerpted from article Extreme Ultraviolet: A New Frontier for Lasers.
Spectrometers currently are available for much of the soft x-ray, extreme UV and VUV regions, although not always in the form in which we are accustomed to seeing. Selecting a spectrometer requires prioritizing analytical goals, wavelength range, spectral resolution, dispersion and possibly optical aperture requirements in light of experimental needs. Shorter wavelengths require ever more care in selection of optical schemes to maintain efficiency and performance.

Rowland circle grazing incidence designs work at 2 or 3 degree grazing angle of incidence useful for wavelengths of greater than one nanometer (energies less than 1000 eV). Other flat field spectrograph designs exist for diagnostics in the 2 keV to 10 eV range. For the most elaborate experiments, hybrid instruments with low pulse stretching, high efficiency and point-to-point imaging for monochromator applications (e.g. to illuminate ARPES samples) or as laser-diagnostic spectrograph are available.

grazing incidence monochromator for analysis and diagnostics of (high) laser harmonics up to about 1000 electronVolts
Grazing incidence monochromator (at UNM Physics) for analysis and diagnostics of (high) laser harmonics

Reference Extreme Ultraviolet: A New Frontier for Lasers

Do you research GaN?

Are you doing research with Gallium Nitride (GaN) and similar materials? Use this material to develop ultraviolet (UV) light emitting diodes (LED) and other ultraviolet UV sensitive devices. McPherson can offer a spectroscopy / material research systems with useful capabilities.

Our spectrometer system has a vacuum tight sample chamber also useful with purge gases. It has a tunable monochromator attached to it and can focus light to the sample (from 120 nanometers up to 800 nanometers). This is great for testing and measuring spectral response, photoluminescence and electroluminescence emission. The system also has a spectrometer system with sensitive charge-coupled detector (CCD) for making quick measurements of light emitted from the sample. This detector works from 200 nanometers to 1000 nanometers. In addition to the emission measurements, this system can also readily measure transmission and reflection, and a variety of angles and wavelengths.

spectrometer system for PL, EL, spectral response, transmission and reflection at any wavelength from 120 to 800 nanometers, and more :)

If you need PL, EL and spectral response information from GaN or related samples contact us about a test and measurement system. We would be happy to talk to you about a user facility or system for your laboratory.

Lighter topic. Still Contentious?

Trout and Ultraviolet Vision

Just saw a blog entry online entitled “Consider reflected UV when tying flies” that is a kind of a book review by Alan Bulmer on the website Active-Angling-New-Zealand.

Many birds, insects and fish (trout!) can see some ultraviolet light that humans cannot. This makes it impossible for us to see “what they are seeing.” While I’ve not read the new book, from the description it sounds like a good treatment of trout flies and their reflection in and of ultraviolet light. It includes many demonstrative photos and special photographic techniques are described in detail.

Interestingly UV wavelengths can really penetrate water, to depths of 55 meters.[?] Thus, fish are able to see objects, either through UV reflectance or UV absorption, at greater depths or in more turbid water than with light in the visible spectrum. Same is true for low light and dark environments. Note this is all concerned with Reflected UV and Not UV excited fluorescence that humans can usually see.

Years ago, I recall somewhat harsh reviews about another title What Fish See. If you have read The New Scientific Angling - Trout and Ultraviolet Vision let me know what you think.

rising trout eats a mayfly

Better spectral measurements

Use a good monochromator to make better spectral measurements. Choose one with more throughput and that works from at least 105 nanometers up to the long wave infrared (LWIR). Use vacuum or a dry purge gas like nitrogen or argon to eliminate absorption by water vapor and oxygen in the vacuum ultraviolet and infrared spectral range. Stainless steel housing, smart materials selection, proper machining techniques and subsequent cleaning permit high vacuum operation (10E-6 mbar range) with o-ring seals.

Many materials have interesting emission or absorbance spectra in the far- and vacuum ultraviolet (VUV) spectral region; the region from 10 to 200 nanometers.(1,2) There are many spectroscopy applications in the VUV. They range from semiconductor process control to fundamental science applications. These include space- and plasma-physics, and attosecond and laser harmonic research. Also, consider UV lasers, optics, crystalline materials, phosphors for more efficient lighting, and resonance Raman instruments.

The diverse applications require a broadly useful instrument. There is no need to custom design. Proven VUV systems make short work of common applications and are ready for challenges. Even silicon charge-coupled device (CCD) and photodiode detectors work at 105 nanometers and more. Thermoelectric cooling and low noise vacuum amplifiers allow you to integrate and collect faint signals.

Do you need an instrument for UV optical reflection and transmission measurement and testing? The new VUV analytical spectrophotometer measures transmission and reflection. It has an optional emission detector path for fluorescent or luminescent samples. The spectrometer features a 200-millimeter focal length optical bench. It has a computer optimized aberration corrected design and a scintillated high gain detector with superior VUV performance. For robust signals in VUV, experiments at wavelengths as low as 120 nanometers, the spectrometer is vacuum compatible and can also be purged with nitrogen or argon.

a deuterium spectrum with some resolved lines

Emission spectrum of a VUV deuterium lamp (magnesium fluoride window) shows clearly defined peaks, with good signal-to-noise performance and 0.1 nm (FWHM) optical resolution collected with 0.1mm wide slits on f/4.7 McPherson Model 207V

Experimental Conditions:
To test performance, we started with a McPherson 207V(3) configured with an 1800g/mm diffraction grating and a 0.1 mm wide slit. A high gain scintillated photomultiplier detector (Hamamatsu R6095) and a source with magnesium fluoride (MgF2) glass window is used. The test sample in this experiment was the VUV deuterium lamp with a VUV-grade MgF2 optical window.
The resultant spectrum shows sharply defined spectral peaks at wavelengths as low as 120 nm, with strong emission peaks around Lyman-Alpha 121 nm and the 159 and 161 nm (see Figure).
We have used the system to measure emission of ionized gases like neon, argon, nitrogen and air. We have directly measured absorbance of water, methanol and acetone solutions in the VUV. Innumerable optical coatings, AR thin films, material batches and crystalline boules have been checked. Even high-resolution applications like measuring H/D ratios are in easy reach.
The results demonstrate that McPherson monochromators excel in VUV applications. If you have spectroscopy experiments or applications in the VUV, look no further. We are happy to be the best-value short-wavelength solution.

1. Wikipedia, web page mentions VUV under larger topic ultraviolet light
2. H. Horspool, F. Lenci, CRC Handbook of Organic Photochemistry and Photobiology, (CRC Press, 2003)
3. web page with full specifications

Light and photonics activities

One hundred educational activities about light and photonics.
With further reference to and also

reference guide with 100 educational activities about light and photonics

The booklet was edited by Silvia Simionato and Pedro Russo, Leiden University. Designed by Robin Allen. It received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 644964. ISBN: 978-94-91760-16-7.

Nuclear-clock transition spotting

Thorium rocks! A nuclear clock that is more precise than any atomic clock available today could soon be a reality, thanks to a discovery made by physicists in Germany. This according to a May article in IOP The groups that produced recent technical papers "Towards a measurement of the nuclear clock transition in 229Th" and "Optical spectroscopy of an atomic nucleus: Progress toward direct observation of the 229Th isomer transition" are both using sensitive McPherson vacuum ultraviolet spectrometers with CCDs setup to detect weak optical emission from crystalline samples excited by 10eV deuterium lamp.

sensitive vacuum ultraviolet spectrometer and CCD setup to detect weak optical emission from crystalline samples excited by 10eV deuterium lamp

Glad to learn these groups (among many others) are making progress on the Thorium front.

SXR spectroscopy w light elements

Lithium is a material used in batteries. Better batteries are required for our phones, cars, space ships and so on. Lithium is the center of a lot of research for this reason. This grazing incidence soft X-ray spectrometer is ideal for measurement of soft X-ray spectra with a low noise back illuminated CCD detector. The movable portion in the spectrometer allows covering a very wide spectral range, from less than 1 nanometer to 300 nanometers overall. This allows the measurement of an entire spectrum for the elements of interest. Lithium for example is around 54 eV. This grazing incidence monochromator can work from 6 to 600 eV and more.

MgOH on Magnesium anode in solid anode electron impact light source for soft x-ray region measured with grazing incidence monochromator equipped with a CCD

MgOH on Magnesium anode

Boron on Magnesium anode in solid anode electron impact light source for soft x-ray region measured with grazing incidence monochromator equipped with a CCD

Boron on Magnesium anode

Graphite (carbon) anode in solid anode electron impact light source for soft x-ray region measured with grazing incidence monochromator equipped with a CCD

Carbon on Magnesium anode

It easily reaches Al-L emission and lower energies. Examples of emission spectra from an electron impact light source for B-K, C-K, and O-K are displayed here now. Others have been collected. Applications range from metals to inorganics, including polymer materials, electronic materials, electronic devices, and batteries. This spectrometer provides insight not available from complimentary energy dispersive spectrometers (EDS). This spectrometer contributes to fundamental understanding of material properties and characteristics. The ability to perform routine chemical state analyses is also expected to make it useful for the practical development, evaluation, and testing of materials.

One meter focal length grazing incidence scanning monochromator equipped with a CCD

CCD equipped grazing incidence spectrometer for soft x-ray region

Some resources for low energy soft x-ray detection:

ICON far ultraviolet instrument for solar physics

The Ionospheric Connection Explorer (ICON) will be the newest addition to NASA’s fleet of Heliophysics satellites. Led by UC Berkeley, scientists and engineers around the world are coming together to make ICON a reality. Read more at Berkeleys Space Science Lab ICON web pages.

The goal of the ICON mission is to understand interaction of Earth’s atmosphere and the space environment. In the ionosphere, at altitudes above 50 miles, a continuous struggle between the Sun and Earth’s weather systems drives extreme and unpredicted variability. ICON will investigate the forces at play in the near-space environment, leading the way in understanding disturbances that can lead to severe interference with communications and GPS signals.

The ICON FUV optics package was shipped to Centre Spatial de Liege (CSL) in Belgium. After verifying visible alignment, the FUV grating and the two FUV cameras will be installed and alignment will begin.

Image Gallery for the ICON FUV Calibration work at CSL Belgium

Image Gallery for the ICON FUV Calibration work at CSL Belgium

News of the FUV instrument shipment to Belgium for calibration

Centre Spatial de Liege (CSL) uses a one meter focal length Model 225 vacuum ultraviolet monochromator to do the far-ultraviolet (FUV) calibration.

Archive from 2014 announcement of clearance for ICON

ICON Twitter Feed | McPherson Twitter Feed

We've known for many years that the Sun has a significant effect on this region of the upper atmosphere. As the Earth rotates, a new portion of its atmosphere is exposed to solar ultraviolet radiation, which heats and partially ionizes the neutral atoms and molecules, creating the ionosphere. At night, when that portion of the atmosphere is not exposed to the Sun, this ionized gas, or “plasma” tends to recombine, dramatically reducing its density as it converts back to an electrically neutral state. In between, near sunset, the low-latitude ionosphere is dominated by a “plasma fountain”, which results in a dramatic upwelling of ionized gas. This results in a sharp increase of the density of ionized gas in narrow bands on either side of the magnetic equator. Basic models of the ionosphere predict that there should be a regular rise and fall of this portion of the atmosphere as the Earth rotates from day to night, independent of longitude.

A few EUV resources

This post directs you to EUV Litho, Inc. a web site promoting EUV Lithography via Workshops, Consulting & Education. In the interest of fast computers and smaller silicon chips (denser) a great deal of work has been done in developing light sources, optical lithography systems and chemistry to enable extreme ultraviolet lithography. The organizing body EUV Litho, Inc. is generously providing access to the proceeding of previous workshops. They are available for download at following links at no cost!

Meeting Information and Workshop Proceedings from SOURCE WORKSHOPS

Meeting Information and Workshop Proceedings from EUVL WORKSHOPS

For example, from 2009, here are the Top 10 Facts Gleaned At EUV Litho Workshop, entire article here

  1. The end of Moore’s Law is always seven years away
  2. You can make 15-nm features with 193-nm light
  3. There’s more than one way to skin an EUV photon
  4. Tin vs. Xenon: This time it’s personal.
  5. Litho nerds have dreams, too
  6. Photoresist: Meet the new boss…
  7. I have to learn French! (AND take a quiz)
  8. EUV Needs A Vacuum
  9. Contamination is bad
  10. No technology is immune from the Star Wars metaphor!

"the preferred method of dealing with line edge roughness–-which according to many attendees is the limiter for lithography-- is shooting a tiny laser (pew! pew! pew!) down the canyon walls of those tiny features to smooth out the rough spots. “It’s like that part where they’re shooting lasers down the canyons in the Death Star,” he explained, warming the nerdiest regions of my heart."

Whole IEEE article here

Light feels good

Ides of March are notorious as the date of the assassination of Julius Caesar in 44 BC. The death of Caesar made the Ides of March a turning point in Roman history. Although March was the third month of the Julian calendar, in the oldest Roman calendar it was the first month of the year!

Rolling through March, we’ve had a few great days with plenty of sunshine and mild temperatures. I have always really liked the feeling of sunshine. I suppose we all do? It makes me feel good and provides a sense of wellbeing. It turns out we're learning more about our interaction with light all the time. Here we take it for granted what frequencies and intensities we encounter. We make the machines to measure that. Nonetheless, it seems study of our interaction with light is just beginning. From alleviating the sensation of pain and treating depression to retrieving memories optogenetics applies precision science to the mysterious workings of our minds. Here are links to a few interesting posts related to this topic, neural and more:

While white, blue, red and amber light all increase migraine pain, low-intensity green light seems to reduce it. The team behind the finding hope that sunglasses that screen out all wavelengths except green could help migraineurs. Many people experience sensitivity to light during a migraine. Photophobia, as it is known, can leave migraineurs resorting to sunglasses in well-lit rooms, or seeking the comfort of darkness.

image from Light Fusion Lab, Germany of a experimental work space with highly controllable lighting

A web post by the US Dept of Veterans Affairs entitled "Can light therapy help the brain?" caught my eye. The therapy is "investigational" but already in use by alternative medicine practitioners to treat wounds and pain. Light from light emitting diodes (LED) has been shown to boost the output of nitric oxide near where the LEDs are placed, which improves blood flow in that location. In the post, they describe how researchers in the VA Boston Healthcare System are testing the effects of light therapy on brain function of Veterans with Gulf War Illness. "We are applying a technology that's been around for a while," says lead investigator Dr. Margaret Naeser, "but it's always been used on the body, for wound healing and to treat muscle aches and pains, and joint problems. We're starting to use it on the brain."

Curious, I browsed for related works and liked this blog post Photon Therapy: Light That Heals". It provides general background about how this works and who has studies it. It turns out our biochemistry is nourished and modulated by light, and benefits greatly from the targeted reception of light frequencies. Light energy at specific wavelengths talks directly to our cells (photobiomodulation), turning on beneficial body chemistry which can help us to restore normal function to tissues, relieve pain and inflammation and rapidly heal from injury, surgery and chronic disease." Read more by following the link.

Even our circadian rhythm is influenced. This "Human Centric Lighting article is great. See also Human Centric Lighting Society. From the paper "...varying light levels are at the heart of a human being’s 24-hour internal clock, otherwise defined as circadian rhythm. Until 200 years ago, 90% of our waking time was spent outside. Now most of us spend 90% of our time indoors with electric lighting. While we’re at work, our lighting is usually set at one light level with a constant correlated color temperature this is not consistent with circadian rhythms. Without regular and direct exposure to such dynamic lighting, the circadian rhythm can be disrupted, which could lead to health issues. Specifically, light and darkness control hormone production. During the day, with a natural circadian rhythm, appropriate amounts of dopamine are secreted for pleasure, alertness and muscle coordination; seratonin for impulse control and carbohydrate cravings; and cortisol for stress response. During the night, melatonin allows for sleep, and refreshes our body"

Another jumping off point Laser Therapy Internet Guide.
Light rules. Have fun and be safe!!

And what starts with the brain eventually ends up with "Nitric Oxide Beads Beat Out Viagra In Treating Erectile Dysfunction". Source: Soni S, Song S, West J, Khera M. Nitric Oxide-Releasing Polymeric Microspheres Improve Diabetes-Related Erectile Dysfunction. Journal of Sexual Medicine. 2013.

Erectile dysfunction (ED) is a highly common problem, affecting pretty much every man at one point or another. It has a profound effect on mood, feelings of self worth and quality of life, leading to anxiety and/or depression. Although traditionally linked to older men and health issues, ED is rapidly increasing in frequency and has become a common problem even in young men. What can red light do to help men suffering from these issues?

June is busy

Just looking forward a bit at all the different things happening at (roughly) the same time...

image from Flugtag yore

  • High-temperature plasma diagnostics (HTPD) meeting, a biennial conference for plasma physicists and engineers. Think magnetic and inertial confinement fusion, space plasmas, astrophysics, and industrial applications. Development of instrumentation, experimental and analytical techniques for the characterization of high temperature plasmas... 5 - 9 June Madison, Wisconsin
  • CLEO brings together aspects of laser technology and offers high-quality content in areas such as ultrafast lasers, energy-efficient optics, quantum electronics, biophotonics and more... 5 – 10 June San Jose Convention Center, San Jose, California, US
  • International Workshop on EUV Lithography focused on the fundamental science of EUV Lithography (EUVL). A smaller group setting suitable for networking and brainstorming... 13 - 16 June at CXRO, Lawrence Berkeley National Laboratory, Berkeley, CA
  • International Conference on Plasma Science (ICOPS) is an annual conference coordinated by the Plasma Science and Application Committee (PSAC) of the IEEE Nuclear & Plasma Sciences Society... 19 - 23 June 2016 Banff, Canada
  • JULY | International conference on Vacuum Ultraviolet and X-ray Physics (VUVX2016) brings together scientists working in fields involving electromagnetic radiation in the vacuum ultraviolet (VUV), soft X-ray and hard X-ray spectral regions generated by synchrotron, laser, or plasma based sources... 3 - 8 July Zurich. Switzerland
  • AUGUST | Red Bull FLUGTAG comes to Boston for the first time ever (video from past events). This one of a kind event will encourage individuals to showcase their creativity in what will be a unique and memorable experience for all who attend. Augut 20, competitors will take the plunge from the DCH Hatch Shell...

Not willing to travel July 4th holiday, sitting out VUVX. Disappointing. The size of CLEO might draw McPherson. These are all interesting topics for high resolution and short wavelength spectroscopy.