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Different velocities of the emitting (or absorbing) particles result in different Doppler shifts, the cumulative effect of which is the emission (absorption) line broadening. [1] This resulting line profile is known as a Doppler profile. A particular case is the thermal Doppler broadening due to the thermal motion of the particles.
An infrared spectroscopy correlation table (or table of infrared absorption frequencies) is a list of absorption peaks and frequencies, typically reported in wavenumber, for common types of molecular bonds and functional groups.
Lipids can be imaged at near-IR wavelengths, with the absorption peak occurring at 930 nm. Water absorbs strongly at near-IR wavelengths longer than 900 nm, with a strong peak at 980 nm. Bilirubin and cytochromes can be imaged at blue wavelengths. UV absorption by DNA has also been exploited to image cell nuclei. [48] [49]
Photoacoustic imaging or optoacoustic imaging is a biomedical imaging modality based on the photoacoustic effect.Non-ionizing laser pulses are delivered into biological tissues and part of the energy will be absorbed and converted into heat, leading to transient thermoelastic expansion and thus wideband (i.e. MHz) ultrasonic emission.
Ultrasound is defined by the American National Standards Institute as "sound at frequencies greater than 20 kHz". In air at atmospheric pressure, ultrasonic waves have wavelengths of 1.9 cm or less. Ultrasound can be generated at very high frequencies; ultrasound is used for sonochemistry at frequencies up to multiple hundreds of kilohertz.
The pump beam can cause the ground state to be depopulated, saturating one transition, while the probe beam finds much fewer atoms in the ground state because of this saturation, and its absorption falls. These crossover peaks can be quite strong, often stronger than the main saturated absorption peaks. [1]
The specificity of absorption spectra allows compounds to be distinguished from one another in a mixture, making absorption spectroscopy useful in wide variety of applications. For instance, Infrared gas analyzers can be used to identify the presence of pollutants in the air, distinguishing the pollutant from nitrogen, oxygen, water, and other ...
The molar extinction coefficient of Hb has its highest absorption peak at 420 nm and a second peak at 580 nm. Its spectrum then gradually decreases as light wavelength increases. On the other hand, H b O 2 {\displaystyle HbO2} shows its highest absorption peak at 410 nm, and two secondary peaks at 550 nm and 600 nm.