INTRODUCTION TO OPTICAL MICROSCOPY.pptx

INTRODUCTION
The optical microscope, also referred to as a light microscope, is
a type of microscope that commonly uses visible light and a system
of lenses to generate magnified images of small objects.
Optical microscopes are the oldest design of microscope and
were possibly invented in their present compound form in the 17th
century .
These used to study the micro and macro structrues of metals.

OPTICAL PRINCIPLE
 It works by a illuminating a metal sample with reflected light
from a light source positioned above the specimen, which is
then magnified by a series of lenses (objective and eyepiece).
Magnification: The ability to enlarge an
image.
Resolution: The smallest distance between
two distinguishable objects

The light path in this optical micro scope is
Light source → Condenser → Specimen →
Objective lens → Eyepiece → Image

COMPONENTS OF OPTICAL MICROSCOPY
 Light Source: Provides illumination
 Condenser Lens: Focuses light onto the specimen
 Objective Lenses: Magnifies the specimen (e.g., 4X,
10X, 40X, 100X)
 Eyepiece (Ocular Lens): Further magnifies the image
 Stage & Stage Clips: Holds the slide
 Coarse & Fine Focus Knobs: Adjusts focus

TYPES OF OPTICAL MICRO SCOPY
 1. Bright-Field Microscopy (BFM)
 Uses a direct light source to illuminate the specimen.
The sample appears dark against a bright background.
 Applications :
 Metallurgical analysis – Studying grain structure and
phases in metals.
 Failure analysis – Identifying cracks, voids, and defects
in materials.
 Surface inspection – Evaluating coatings and treatments

2. Dark-Field Microscopy (DFM)
 Uses an oblique light source, meaning light does not pass directly
through the specimen.
 Only scattered light enters the objective lens, making the specimen
appear bright on a dark background.
 Enhances contrast for fine details.
 Applications :
 Detecting micro-cracks and surface imperfections in metals.
 Analyzing thin films and coatings in materials science.
 Studying wear patterns in machined surfaces.

3. Polarized Light Microscopy (PLM)
 Uses polarized light to analyze materials with birefringence
(optical anisotropy).
 When light passes through certain materials, it splits into two
rays with different velocities, creating contrast.
• Applications :
• Analyzing crystalline structures in metals, alloys, and
ceramics.
• Identifying phases in composites and polymer materials.
• Studying stress patterns in transparent materials (e.g., glass,
plastic

Differential Interference Contrast (DIC)
Microscopy
 The polarized light is dispersed into two distinct light rays with
an orthogonal plane of polarization using wollaston prism.

APPLICATIONS:
Examining microstructures of metals.
Surface texture analysis in precision
machining.
Defect detection in coatings

SPECIMEN PREPARTION
1.Sample Selection & Cutting:
 To obtain a small, manageable piece of the material for
analysis.
 For the metals: Use a saw, laser cutter, or precision cutting
tools.

2. Mounting:
 To stabilize the specimen for easier handling under the
microscope.
 Use a mounting material that does not interfere with optical
analysis.
 For small or irregular samples: Embed in resin or epoxy.
 3. Grinding & Polishing (for Metals & Materials):
 Grinding: Use coarse to fine abrasive papers
 Polishing: Use a soft cloth with fine diamond
.

4.Etching (for Metals & Alloys):
 To reveal micro structural features such as grain
boundaries and phases.
Nital (2% nitric acid in ethanol) – for steel.
Keller’s reagent – for aluminum alloys.
Hydrofluoric acid – for titanium and ceramics

5. Final Cleaning & Drying:
 To remove any contaminants before microscopic observation.
 Ensure no dust particles are present on the specimen

INTRODUCTION TO OPTICAL MICROSCOPY.pptx

More Related Content

Similar to INTRODUCTION TO OPTICAL MICROSCOPY.pptx

Recently uploaded

INTRODUCTION TO OPTICAL MICROSCOPY.pptx