Chapters 4.3 & 4.4: Optical Microscopy/ Electron Microscopy

What are the three steps of fluorescence?

-absorption of a photon -loss of some energy -re-emission to a lower wave length

What are disadvantages of dark field microscopy?

-samples can have a glare -see a silhouette rather than a defined object

What are advantages of dark field microscopy?

-the enhanced ability to see details on a biological specimen that does not have much contrast -the technique is simple and cheap

What is magnification of a transmitting electron microscope?

10,000X to 100,000X

What size range can be used for bright field optical microscopy?

1000 mm (1 micrometer) to 5 mm

What is magnification of a scanning electron microscope?

10X to 100,000X

What does an image look like through a stereo microscope?

3D image of the specimen's surface

What range of wavelengths can be used for infrared microscopy?

700 nm (nanometers) to 1400 nm

Using a dark field microscope, what would you see if you looked into the lens without a sample underneath?

A black field

What is an another name for a stereo microscope?

A dissecting microscope

Using a dark field microscope, what would you see if you looked into the lens with a sample underneath?

An illuminated sample

What compounds absorb light in the infrared region?

Drugs, bullets, fingerprints, dyes and cancer cells

What is the property of birefringence?

Light that is refracted in two separate rays

What types of forensic samples are used with a polarized light microscope?

Minerals, crystals, and synthetic fibers

Why is fluorescence microscopy useful when investigating possible art fraud?

Old paints do not fluoresce while new paints do

What two techniques are used in electron microscopy?

Scanning electron microscopy and transmitting electron microscopy

What is the most commonly used microscope in forensics and why?

The stereo microscope because it has a wide field of view, great depth of focus, and uses normal light

Why are comparison microscopes essential for forensics?

They can compare hairs and fibers, contrast firearms, and illegitimate documents

Why do forensic scientists use fluorescence microscopy?

To analyze victims of sexual assault and to analyze sperm stains

What are comparison microscopes used for?

To compare fine details on two different samples

What is the purpose of using a phase contrast microscope?

To enhance contrast in colorless samples

Why must biological samples be stained?

To provide more contrast

What is optical microscopy?

Visible light is used to illuminate a sample, which allows the naked eye to "see" it

What light is used in bright field optical microscopy?

White light

What is plane-polarized light?

light confined to a single plane of vibration