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Fiat Lux Review of the Electro-Magnetic Spectrum. Kate Martin McCrone Associates, Inc. Outline. Historical understanding of light Properties of light Light beyond the visible region Electromagnetic spectrum Spectroscopy Regions of the spectrum Radio Microwave Infrared Visible

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fiat lux review of the electro magnetic spectrum

Fiat LuxReview of the Electro-Magnetic Spectrum

Kate Martin

McCrone Associates, Inc.

  • Historical understanding of light
  • Properties of light
  • Light beyond the visible region
  • Electromagnetic spectrum
  • Spectroscopy
  • Regions of the spectrum
    • Radio
    • Microwave
    • Infrared
    • Visible
    • Ultraviolet
    • X-ray
    • γ-ray
google hits
Google Hits
  • Spectroscopy 18,500,000
  • Spectroscopy and materials 10,200,000
  • Spectroscopy and chemistry 9,370,000
  • Spectroscopy and biology 3,320,000
  • Spectroscopy and polymers 2,380,000
  • Spectroscopy and food 2,060,000
  • Spectroscopy and astronomy 1,510,000
what is the electromagnetic spectrum
What is the electromagnetic spectrum?
  • Broadcast signal
  • Dental x-ray
  • Rainbow
  • Supernova burst
  • Sunburn
  • Fireworks
  • Medical imaging

Electromagnetic Spectrum

low frequency high frequency

long wavelength short wavelength

Courtesy of the Advanced Light Source, Berkeley Lab

aristotle 350 bce
Aristotle (~350 BCE)
  • “Thus, pure light such as that from the sun, has no color, but is made colored by its degradation when interacting with objects having specific properties which then produce color.”
  • This was the common view for about 20 centuries.
isaac newton 1642 1727
Isaac Newton (1642 – 1727)

Portrait of Isaac Newton in 1689

(aged 46 years)

what does a prism do
What Does a Prism Do?
  • Prisms already a well-known toy in Newton’s day
  • Color was believed by many to be a homogeneous mixture of light and dark and that prisms acted to modify the light (that is, prisms added the color)
  • Newton demonstrated that prisms did not modify light; they acted to separate light into its constituent colors; thus, light is heterogeneous
experimentum crucis 1666
“Experimentum Crucis” ~1666

White light was first decomposed into its constituent colors,

then recombined back into white light, then separated again.

Light was further deflected by subsequent prisms, but the

color was not modified.

Thus, white light is a heterogeneous mixture of differently

refrangible colors.

not everyone agreed
Not Everyone Agreed

1790 - Johann Wolfgang von Goethe

Light is “the simplest most undivided most homogenous being that we know. Confronting it is the darkness“

“Yellow is a light which has been dampened by darkness”

“Blue is a darkness weakened by the light”

nature of light early ideas
Nature of Light (Early Ideas)
  • Corpuscle (particle) nature (Newton)
    • Red corpuscles the largest (the least deflected)
    • Violet corpuscles the smallest (greatest deflection)
  • Wave nature (Christian Huygens)
    • “Movement within a fine medium”
    • Did not intially recognize variation in wavelengths
wave nature of light
Wave Nature of Light



y= amplitude

c= speed of light in a vacuum

f = frequency (cycles per second)

properties of light
Properties of Light
  • Refraction
    • Light passing from one medium into another changes direction
    • With a prism, blue light shows a greater change in direction than red light
  • Diffraction
    • Apparent bending of light around small obstacles
  • Reflection
    • Change of direction at an interface such that light returns back to the original medium
    • Specular (mirror-like) reflectance: angle of incidence equals angle of reflectance
  • Scattering
    • Diffuse reflectance, internal reflectance
  • Absorption
  • Transmittance
Is the straw broken?

No, we see the straw through different media, with different refractive indices


Light bends as it goes

from air into the glass

balls, and then again as

it goes back into air


n =

Refractive Index

Velocity of light in a vacuum

Velocity of light in a medium

refractive index
Refractive Index
  • Materials may have one or more refractive indices
    • Air 1.000293
    • Water 1.3330
    • Borosilicate Glass 1.470
    • Diamond 2.419
    • Calcite (CaCO3) 1.49, 1.66
  • Materials with two or more refractive indices are birefringent

a crystal of


refractive index23
Refractive Index
  • Identification
    • Solids – Light Microscope
      • Minerals
      • Glasses
      • Powders
    • Liquids – Refractometer, HPLC detector
      • Water
      • Organics
      • Solutions
    • Gases
  • Purity
  • Concentration
  • Calculate focusing power of lenses
  • Calculate dispersive power of prisms
  • Hologram on a credit card (diffraction grating)
  • Rainbow pattern on a CD or DVD
  • Bird feathers

a spider web’s color

is partially due to diffraction

  • Diffraction is the apparent bending that occurs for a wave when it encounters an obstacle, or the spreading out of a wave past small openings

circular aperture (Airy disk)

slit which is 4 wavelengths long

  • X-ray diffraction
    • Location and distances between atoms in a crystal
  • Holography
    • Mixing of a laser beam and unfocused diffraction pattern of some object
  • Diffraction grating as a dispersive element
    • monochromator
  • Seeing yourself in a mirror
  • Reflection of sun in lake waters
  • Mirage in the desert
  • Light, sound and water waves undergo reflection
  • Reflection of VHF is important for radio transmission and radar
  • Hard x-rays and gamma rays can be reflected with grazing angle mirrors

Double reflection – sun reflected in water and again in the paddle

Caravaggio, “Narcissus”

scattering diffuse
Scattering (Diffuse)
  • Light, sound, particles can all be scattered
  • Defined as a deviation from a straight trajectory by one or more localized non-uniformities
  • Scattering centers include bubbles, particles, irregular surfaces (sandpaper), droplets, defects in crystals, surface roughness, textured (fibrous) clothing, etc.
  • Areas that use scattering measurements include medical imaging, radar, inspection of silicon wafers, process monitoring (polymer synthesis), computer imagery
  • Elastic Scatter (wavelength is unchanged upon scattering)
    • Mie:
      • Scattering center ~ wavelength or larger
      • Shape-dependent
      • Wavelength independent
      • White clouds (water droplets are larger than air molecules)
    • Rayleigh:
      • Scattering centers small compared to wavelength (<1/10)
      • Wavelength dependent I ∞ 1/Λ4
      • Scattering at 400 nm is 9.4 x that at 700 nm
      • Blue sky (air molecules are small compared to visible light)
  • Inelastic scatter (wavelength is changed upon scattering)
    • Raman, Compton, inelastic x-ray

Absorption / Transmission

  • Light absorbed by a material may impart some of its energy (for example, as heat)
  • Absorption/transmission is selective:
    • Dark materials absorb most/all visible wavelengths
    • Glass transmits visible light, but absorbs UV
    • Chlorophyll absorbs blue and red, and reflects green
  • Absorbance can be used to quantify a material, as in the Beer-Lambert Law

A = ελ x b x c

      • A = absorbance
      • ελ = wavelength-dependent absorptivity coefficient
      • b = pathlength
      • c = concentration
adventures of a beam of light
Adventures of a Beam of Light

Emission (fluorescence)

Light IN

internal reflectance




Light OUT




Semi-transparent material

When the sun is near the horizon, its rays pass through more atmospheric particulate than when overhead (longer pathlength)

Short wavelengths are efficiently scattered away, leaving red light to reach your eye

Why is the Sunset Red?


Discovery of Non-Visible Light - I

Sir Frederick William Herschel 1738 - 1822

sir frederick william herschel
Sir Frederick William Herschel
  • Astronomer, discovered the planet Uranus (1781)
  • Noticed that differently colored filters appeared to pass different amounts of heat from sunlight
  • 1800: Measurement of color temperatures using thermometers and a glass prism to separate light into component colors
  • Temperature increased from violet to red
  • Highest temperature just outside the red (calorific rays)
  • Calorific rays underwent reflection, refraction, absorption, transmittance like visible light

Discovery of Infrared

Crude temperature measurements of light

discovery of non visible light ii
Thought that nature had “polarity” and if radiation existed outside one end of the visible light spectrum, it must exist outside the other end.

1801: Glass prism and paper soaked in AgNO3 – blue light darkens AgNO3 more/faster than red.

Just beyond the violet – it darkens even more!

“Chemical rays” now known as ultraviolet

Independently discovered in 1802 by William Hyde Wollaston

Discovery of Non-Visible Light- II

Johann Wilhelm Ritter

born in 1776 in Samitz, Silesia

electro magnetic
Electro + Magnetic
  • Oersted (1820):
    • Electrical and magnetic fields first associated in 1820
    • Electrical current through a wire could produce deflection in a compass needle
  • Ampere:
    • Two wires conducting electrical current could repel each other
  • Faraday (1847):
    • Proposed that light was a high frequency electromagnetic vibration
  • Maxwell (1864):
    • Mathematically explained link between electricity and magnetism
    • Determined that visible light was a form of EM radiation
the photon
The Photon
  • The photon (from Greek "phos", meaning light) is the quantum of the electromagnetic field (smallest unit). The term photon was coined by Gilbert Lewis in 1926.
  • In some respects a photon acts as a particle, for instance when registered by the light -sensitive device in a camera.
  • In other respects, a photon acts like a wave, as when passing through the optics in a camera.
electromagnetic spectrum
Electromagnetic Spectrum

E = hc/λ f = c/λ

E = Energy of a photon

h = Planck’s constant, 6.626 x 10-34 J•sec

c = speed of light in a vacuum, 3.0 x 108 m/sec

λ = wavelength (m)

f = frequency (Hz)








< 3x109 Hz

3x109 – 3x1011 Hz

3x1011 – 4x1014 Hz

4x1014 – 7.5x1014 Hz

7.5x1014 – 3x1016 Hz

3x1016 – 3x1019 Hz

> 3x1019 Hz



> 10 cm

10 – 0.1 cm

1000 – 0.7 µm

700 – 400 nm

400 – 10 nm

10 – 0.01 nm

< 0.01 nm

  • Interaction of light with matter to study certain chemical and physical properties of matter
  • Now generally includes use of particles (mass) or alternating field in addition to light
  • ~130 types of spectroscopy
    • Identification
    • Structure
    • Quantitation
    • Physical properties
interaction of em with matter
Interaction of EM with Matter

interactions with matter
Interactions with Matter

Nuclear spin

Molecular rotations

Molecular vibrations

Outer shell electrons

Molecular dissociation

Inner shell electrons

Nuclear transitions








spectroscopy and ghosts
Spectroscopy and Ghosts

Isaac Newton coined the term “spectrum”, based on the Latin “spectre”, meaning ghosts

origins of spectroscopy
Origins of Spectroscopy
  • 1666 – Isaac Newton’s discovery that white light is composed of multiple colors
  • 1814 - Joseph Fraunhofer took a spectrum of the sun and discovered dark lines
  • 1857 - Gustav Kirchhoff and Robert Bunsen discovered that each element has a unique spectral signature
fraunhofer lines
Fraunhofer Lines

~590 nm sodium “D” line

~570 Dark lines observed in the spectrum of the sun

Each chemical element associated with a set of lines

Dark lines from absorption of specific wavelengths by elements

  • Emission
    • Atomic emission (OES, AES)
    • Fluorescence
    • Raman
  • Absorption
    • Infrared
    • NMR
    • UV-visible
    • Microwave
    • X-ray absorption spectroscopy
    • Atomic absorption
    • Mossbauer
emission fireworks
Red: Lithium and strontium

Orange: Calcium

Yellow: Sodium

Green: Barium

Blue: Copper

Silver: Aluminum, Titanium, Magnesium

Emission - Fireworks
atomic emission spectroscopy
Atomic Emission Spectroscopy
  • Analyte atoms are solubilized
  • Aspirated into flame, discharge or plasma
  • Electrons promoted into higher energy states
  • Decay to lower energy with emission of photons
  • Wavelength of emitted photons depends on nature of atom
  • Discrete, narrow bands
absorption spectroscopy


infrared light

light transmitted

through sample



infrared light

light reflected

from sample


Absorption Spectroscopy
  • Measurement of light transmitted or reflected after passing through a sample
radio waves
Radio Waves
  • The longest waves in the EM spectrum
    • Longest are longer than a football field
    • Shortest are about the size of a football
  • Human body is transparent to radio waves
  • Earth’s atmosphere is transparent to all but long wavelength
  • Radio, television, cell phones, wireless networks
  • NMR (nuclear magnetic resonance) spectroscopy
  • Magnetic resonance imaging (MRI)

NMR Spectroscopy

In an applied magnetic field, nuclei of certain atoms will line up parallel or anti-parallel to the field

I = n½ : 1H, 13C, 15N, 19F, 31P

When irradiated with certain radio frequencies, the nuclei at lower energy can “spin-flip” to the higher energy state

Absorption of radio waves measured (NMR spectra)

applications of nmr
Applications of NMR
  • Identification
  • Structure elucidation
  • Molecular dynamics in solution
  • Diffusion coefficients
  • Imaging (MRI)
  • Wavelengths on the order of centimeters
  • Human body is largely transparent
    • Conductors absorb microwaves
  • Longer microwaves used in microwave ovens
    • 2.45 GHz (12.24 cm)
    • Water and other polar molecules rotate
  • Shorter microwaves used for remote sensing
  • Molecular rotations
microwave spectroscopy
Microwave Spectroscopy
  • Molecules have rotational energies corresponding to energies in the microwave region
  • The EM field exerts a torque on a molecule with an electric dipole moment
  • Polar molecules can rotate much faster upon exposure to microwaves
  • Size of molecule can be determined by wavelengths absorbed
    • Bond lengths of diatomic molecules
vibration rotation spectrum
Vibration-Rotation Spectrum

ground vibrational state 1st excited vibrational state

v = 0 v = 1

vibration rotation spectrum of hcl
Vibration-Rotation Spectrum of HCl

splitting due to 35Cl and 37Cl isotopes

infrared region67
Infrared Region
  • Measured in micrometers
  • Human body absorbs infrared radiation
    • Penetrates skin tissue
    • Heat!
  • Largely blocked by Earth’s atmosphere
  • Water strongly absorbs infrared radiation
  • Longer wavelengths
    • Heat lamps
  • Shorter wavelengths
    • TV remotes
  • Molecular vibrations
infrared regions
Infrared Regions
  • Far-infrared
    • 1000 µm to 10 μm
    • Rotational modes in gases
    • Molecular motion in liquids
    • Phonon modes in solids
  • Mid-infrared
    • 10 µm to 2.5 μm
    • Blackbody radiation
    • Fundamental molecular vibrations
  • Near-infrared
    • 2500 nm to 750 nm (2.5 µm to 0.75 µm)
    • Overtones and combination bands of fundamental vibrations (weak vibrations)
terahertz spectroscopy
Terahertz Spectroscopy
  • Between microwave and infrared
  • 0.06 THz – 3 THz
    • 2 cm-1 – 100 cm-1
    • 5000 µm – 100 µm
  • Inter-molecular interactions
  • Pharmaceuticals
    • Polymorphs
    • Hydration state
    • Tablet imaging
    • Protein conformation
  • Homeland Security
    • Detection of noxious gases
    • Explosives
infrared spectroscopy
Infrared Spectroscopy
  • Molecular bonds vibrate upon absorption of specific energies (usually in the infrared region)
  • In order to absorb IR, bond must undergo a change in its permanent dipole
  • Measure emissions in automobile exhaust
  • Most widely used spectroscopy
  • Applications:
    • Identification of unknowns
    • Verification of raw materials (QC)
    • Structure elucidation
oxidative hair damage
Oxidative Hair Damage

Scission of S-S bond to form sulfonic acid (cysteic acid)




Cy-S-S-Cy Cy-S-S-Cy Cy-S-S-Cy Cy-SO3-

O O2

infrared spectra of hair atr

2nd derivative spectra

untreated hair

colored hair (15x L'Oreal)


colored hair (15x L'Oreal)



amide III (1240 cm-1)

untreated hair


cysteic acid (1240 cm-1)




















Infrared Spectra of Hair (ATR)
near infrared spectroscopy
Near-Infrared Spectroscopy
  • Overtones and combinations of fundamental vibrations
  • Broad overlapping bands
    • Not highly useful for identification
  • Very sensitive to hydrogen-bonding
    • Probe aqueous environment
  • Subtle changes in spectra related to chemical and physical properties
  • Chemometrics
nir applications
NIR Applications
  • Agriculture
    • Hand-held devices in the field
  • Medical
    • Body fat analysis
    • Glucose monitoring
    • Hemoglobin in infants
  • Process monitoring
    • Polymers
    • Surfactants (e.g., hydroxyl value)
  • Quality control
    • “Prediction” of physical and sensory properties
      • Taste of peas
      • Wine quality
raman spectroscopy

inelastically scattered light (Raman)

(different wavelength)

laser light

(incident light)

scattered light (Rayleigh)

Raman Spectroscopy







Raman versus Infrared

Scattering (Raman) Absorption (IR)

non-polar groups polar groups

Raman shift: the difference between the excitation wavelength and

the wavelength of the inelastically scattered photon

applications of raman spectroscopy
Applications of Raman Spectroscopy
  • Identification of unknowns
  • Study of carbon polymorphs
    • Carbon nanotubes
    • Diamond manufacturing
  • Structure elucidation
  • Strain / stress in silicon
  • Polymer orientation
  • Polymorphs of pharmaceutical actives
color system reaction time
Color System Reaction Time


mixed system,

0 - 30 minutes

Piedmont blonde hair

visible and ultraviolet light
Visible and Ultraviolet Light
  • 700-400 nm (visible)
  • 400-10 nm (UV)
  • UV is strongly absorbed by ozone layer
  • Human body strongly absorbs visible and UV light
    • Sunburn (297 nm gives maximum burn)
    • Skin cancer
  • Electronic transitions (outer shell)
    • Electrons can be excited to higher energy states
  • Photoionization (UV)
  • Quantitative measurement of solutions of transition metal ions and conjugated organic compounds
  • UV region: DNA and protein
uv spectra of polyenes
UV Spectra of Polyenes

Adding conjugation

shifts λmax to longer


fluorescence spectroscopy
Fluorescence Spectroscopy
  • Process by which molecules emit light
  • Absorption of photon of shorter wavelength followed by emission of photon of longer wavelength
  • Fluorescent dyes may absorb UV light and emit visible light, e.g.
  • May be very sensitive to molecular environment (biological probes)
  • High sensitivity – single molecule detection
fluorescence spectroscopy83
Fluorescence Spectroscopy

x ray radiation85
X-Ray Radiation
  • On the order of Ångstroms or nanometers
  • Human body is fairly transparent
    • Soft tissue
  • Blocked by Earth’s atmosphere
  • Produced by sun, black holes
  • Ionizing radiation
  • Absorption and emission
  • Imaging
  • Inner shell electrons
x ray fluorescence
X-Ray Fluorescence

Electron in K-shell

ejected out of atom

after bombardment

of an external x-ray

Vacancy is filled by

an electron in L or M,

emitting characteristic

x-ray in the process

Identification of


x ray absorption spectroscopy
X-Ray Absorption Spectroscopy
    • Extended X-ray absorption fine structure
    • X-ray absorption near-edge structure
    • X-ray absorption spectroscopy
  • Synchrotron radiation source
  • Gas phase, liquids, solids
  • Sensitivity to local structure
x ray diffraction
X-Ray Diffraction
  • Elastic scattering of x-rays
  • Materials with long-range order
  • Crystallographic structure
  • Chemical composition
  • Physical properties

Structure of a snowflake

determined by x-ray cystallography,

showing hexagonal symmetry

gamma radiation
Gamma Radiation
  • Shortest waves in the EM spectrum (most energetic)
    • On the order of < 0.1 Å (overlaps x-ray)
  • Human body is largely transparent
  • Earth’s atmosphere blocks γ-rays
  • Can pass through 3 meters concrete
  • Ionizing radiation
    • Kills cells, induces mutations, chromosomal damage
    • Cancer treatment
  • Nuclear transitions
  • Produced by supernovas, nuclear reactions, neutron stars, radioactive decay

mossbauer spectroscopy
Mossbauer Spectroscopy
  • Resonant emission and absorption of gamma rays
  • Nuclear transitions
  • Solid matrix
  • Iron-bearing minerals

applications of spectroscopy
Applications of Spectroscopy
  • Biotechnology
  • Biomedicine
  • Dentistry
  • Food / Beverage
  • Agriculture / Pesticides
  • Forensics and WMD
  • Polymers and Coatings
  • Catalysis
  • Water treatment
  • Energy
  • Art conservation
  • Chemical imaging
bio medical applications of nir
Bio-Medical Applications of NIR

Near-infrared spectroscopy

can be used for monitoring

brain function via

hemoglobin activity

in newborns with critical

health problems because it

is non-invasive and portable

biotechnology nmr
Biotechnology - NMR

1H NMR spectra of phospholipid liposomes

Used as tooth-bonding agents

pH-Dependent Complexation of Methacryloyloxydecyl Dihydrogen Phosphate (MDP) with Dipalmitoylphosphatidylcholine (DPPC) Liposomes: DSC and NMR Measurements Seiichiro Fujisawa1, et al.

food and beverage quality icp aes
Food and Beverage Quality – ICP-AES

Trace metals in wine, mercury in fish


Forensics – Infrared Spectroscopy

red-brown material from right side of right shoe

A Case of Vehicular Homicide

refined Trinidad lake asphalt (reference)

(slides courtesy of S. Stoeffler)

process monitoring nir
Process Monitoring - NIR

Near-infrared spectrometer in use on a conveyor belt

water treatment fluorescence
Water Treatment - Fluorescence

Fluorescence excitation emission of raw water Fulvic-like fluorescence (Peak C), Humic-like fluorescence (Peak A)

Tryptophan-like fluorescence (Peak T).

art conservation xrf
Art Conservation - XRF

Bruker micro-XRF IAEA’s XRF at Kunsthistorisches

chemical imaging
Chemical Imaging

Mid-infrared image showing release of SF6 and NH3

at 1.5 km

chemical imaging fluorescence
Chemical Imaging - Fluorescence

Normal tissue Severe Dysplasia

Protein-bound NADH lifetimes measured in vivo

in the DMBA-treated hamster cheek pouch model

of oral carcinogenesis

em spectrum in the comics
Superhero Triumph

Super Power:

Ability to control the electromagnetic spectrum

EM Spectrum in the Comics