Photoacoustic Spectroscopy

1
Photoacoustic Spectroscopy
2
Introduction

• photoacoustic the measurement of the effected
  spectroscopy of absorbed electromagnetic energy
  (particularly of light) on matter by means of
  acoustic detection.
• The discovery of the photoacoustic effect dates
  to 1880 when Alexander Graham Bell,
• Next Bell showed that materials exposed to the
  non-visible portions of the solar spectrum can
  also produce sounds.

3
Bell photoacoustic effect

• The photoacoustic (PA) or optoacoustic (OA)
  effect, i.e. the generation of acoustic waves due
  to the absorption of modulated electromagnetic
  waves, is an old effect, discovered by Bell in
  1880.
• This effect is weak only a very small fraction
  (lt1ppm) of the absorbed optical energy is
  converted into acoustic energy.

4
(No Transcript)
5
Principle of Photoacoustic Spectroscopy

• A photoacoustic spectrum of a sample can be
  recorded by measuring the sound at different
  wavelengths of the light.
• This spectrum can be used to identify the
  absorbing components of the sample. The
  photoacoustic effect can be used to study solids,
  liquids and gases.
• SampleLight-electon.

6
(No Transcript)
7
(No Transcript)
8
How it works

• Sample.
• Far IR.
• Electron Excitation.
• Acoustic Waves.
• Microphone.
• Spctra analaysis.
• Result.

9
(No Transcript)
10
Electron Excitation

• As light is absorbed electrons are excited either
  electronically or vibrationally. When looking at
  electronic excitation, electrons jump to a higher
  energy level.
• As they drop back to its ground state, the extra
  energy is given off as heat. Collision
  deactivation, another form of heat formation,
  involves the colliding of atoms. The collision of
  atoms give off energy in the form of heat.
• However in the case of electronic excitation,
  the energy can also be dissipated through
  chemical reactions or radiative emissions as seen
  in figure.

11
(No Transcript)
12
Acoustic Waves  

• With the formation of heat, thermal expension
  heat, also occurs. The expansion of heat creates
  localized pressure waves and in turn, can be
  measured as an acoustic wave.
• With acoustic waves sent after every pulse of
  light, a sensor can then measure the waves.
• Acoustic wave can be measured and plotted to form
  a spectrum of the material.

13
(No Transcript)
14
Importance of Photoacoustic Spectrometry

• PAS may seem similar to other infrared techniques
  such as Fourier transform infrared
  spectroscopy(FTIR).
• PAS does not measure the effect relative to the
  background but directly from the sample, making
  it extremely accurate.
• Types
• The Gas-Coupling Method,
• The Direct Coupling Method.

15
Applications

• PAS is used for both qualitative and quantitative
  analysis of sample.
• PAS is used for analysis of biological gases
  sample.
• PAS is use for durg properties analysis
  (Polystyrene , Aspirin, Paracetamol etc).
• All sample use this PAS (solid,gas,liguid).
• Monitoring of gas and water qualities
  enviroments.
• Monitoring and inspection of foods and
  agricultural products.
• Monitoring human helath condition .

16
Type
17
(No Transcript)
18
(No Transcript)
19
(No Transcript)