Microscopy Quiz 4

Generally what does the ATR formula describe?

ATR (attenuated total reflectance) describes the penetration depth in a sample of the evanescent wave.

What is the ATR determined by?

Refractive indices of the sample and reflection element

Angle of incidence

Wavelength of light

How is diffraction controlled in an IR microscope?

Aperture control

NA

Wavelength selection

Mirror use

Why are mirrors used in an IR microscope?

So that a phase difference can be applied to one of the two split beams of light and recombined. Also allows for IR light to be directed and focused.

What are the sample requirements for ATR analysis?

Sample has a lower refractive index than that of the ATR element

Sample must be in intimate contact with the ATR element

What is special about IR microscope optics?

Reflective optics used instead of glass lenses

Apertures are above and below the sample

IR light is used instead of visible light

Higher NA

Why does the IR microscope have a separate detector?

Because IR light is not visible to the naked eye, and using an external detector allows for chemical information to be determined.

Why are apertures not placed on the sample?

Apertures must be placed at the image-formation position of the radiation source. Spatial selectivity

What is melting point and how is it different than melting range?

Melting point is the temperature when a solid turns to a liquid.

The melting range is the temperature interval between when a substance first starts melting and when it has completely melted.

Melting point is typically for pure crystalline samples, while melting range is for mixed samples or samples that have contaminants (fibers). There is a difference because of purity.

Why is PLM useful for Thermal Microscopy?

The birefringence of a sample changes as it melts, therefore, using PLM with thermal microscopy allows for the observation of how a sample’s birefringence, and thus crystal structure, changes while it is heated.

The changes can be compared between the known and questioned samples.

What is special about the mounting medium for Thermal Microscopy?

Silicone oil is used as a mounting medium since:

it is inert with respect to fibers

improves contrast of fibers

improves the thermal contact between the sample and the hotstage.