When light passes through a small opening, comparable in size to the wavelength λ of the light, the wavefront on the other side of the opening resembles the wave. Let us know more about the diffraction of light and single slit diffraction that occurs when light travels through a single slit. Also, let us learn what happens in a single slit diffraction experiment.

Revolving Nosepiece or Turret: This is the part of the microscope that holds two or more objective lenses and can be rotated to easily change power.

Compton effect is defined as the effect that is observed when x-rays or gamma rays are scattered on a material with an increase in wavelength.

When light travels in air, it encounters various phenomena like interference, refraction, reflection and diffraction. When the light comes in contact with an obstacle, diffraction of light takes place.

Diffractionof waves

We can observe single slit diffraction when light passes through a single slit whose width (w) is on the order of the wavelength of the light. The diffraction pattern on the screen will be at a distance L >> w away from the slit. The intensity is a function of angle.

Eyepiece/Ocular: Compound microscopes commonly have a pair of eyepieces that provide binocular vision. Other microscopes may have a single eyepiece or sometimes no eyepieces at all.

Objective Lenses: Compound microscopes have multiple objective lenses mounted on a rotating nosepiece, typically with magnifications ranging from 4x to 100x or higher. Other microscopes, such as dissecting or stereo microscopes, usually have fixed magnification lenses.

1. Ocular eyepiece lens to look through. 2. Objective lens, closest to the object. Before purchasing or using a compound microscope, it is important to know the functions of each part. This information is presented below. Links will take you to additional information and images.

The condition for destructive interference is that the path difference should be equal to an odd integral multiple of half wavelength.

We shall identify the angular position of any point on the screen by θ measured from the slit centre which divides the slit by a/2 lengths. To describe the pattern, we shall first see the condition for dark fringes. Also, let us divide the slit into zones of equal widths a/2. Let us consider a pair of rays that emanate from distances a/2 from each other as shown below.

How to Focus Your Microscope: The proper way to focus a microscope is to start with the lowest power objective lens first and while looking from the side, crank the lens down as close to the specimen as possible without touching it. Now, look through the eyepiece lens and focus upward only until the image is sharp. If you can't get it in focus, repeat the process again. Once the image is sharp with the low power lens, you should be able to simply click in the next power lens and do minor adjustments with the focus knob. If your microscope has a fine focus adjustment, turning it a bit should be all that's necessary. Continue with subsequent objective lenses and fine focus each time.

Magnification: Compound microscopes are designed for higher magnifications, typically used for observing microscopic details. Other microscopes may have lower magnification capabilities, suitable for larger specimens or samples.

Definition ofdiffractionin Physics

The maxima lie between the minima and the width of the central maximum is simply the distance between the 1st order minima from the centre of the screen on both sides of the centre.

Objective Lenses: Usually you will find 3 or 4 objective lenses on a microscope. They almost always consist of 4x, 10x, 40x and 100x powers. When coupled with a 10x (most common) eyepiece lens, total magnification is 40x (4x times 10x), 100x , 400x and 1000x. To have good resolution at 1000x, you will need a relatively sophisticated microscope with an Abbe condenser. An Abbe condenser is composed of two lenses that control the light that passes through the specimen before entering the objective lens on the microscope. The shortest lens is the lowest power, the longest one is the lens with the greatest power. Lenses are color coded and if built to DIN standards are interchangeable between microscopes. "DIN" is an abbreviation of "Deutsche Industrial Normen". This is a German standard that has been adopted internationally as an optical standard used in most quality microscopes. A typical DIN standard microscope objective lens has a 0.7965" (20.1mm) diameter threads, 36 TPI (threads per inch), and a 55º Whitworth. Many high power objective lenses are retractable (i.e. 40XR). This means that if they hit a slide, the end of the lens will push in (spring loaded) thereby protecting the lens and the slide. All good quality microscopes have achromatic, parcentered, parfocal lenses.

Fraunhoferdiffraction

Condenser Lens: The purpose of the condenser lens is to focus the light onto the specimen. Condenser lenses are most useful at the highest powers (400x and above). Microscopes with in-stage condenser lenses render a sharper image than those with no lens (at 400x). If your microscope has a maximum power of 400x, you will get the maximum benefit by using a condenser lenses rated at 0.65 NA or greater. 0.65 NA condenser lenses may be mounted in the stage and work quite well. A big advantage to a stage mounted lens is that there is one less focusing item to deal with. If you go to 1000x then you should have a condenser lens with an N.A. of 1.25 or greater. All of our 1000x microscopes use 1.25 Abbe condenser lens systems. The Abbe condenser lens can be moved up and down. It is set very close to the slide at 1000x and moved further away at the lower powers.

For the next fringe, we can divide the slit into 4 equal parts of a/4 and apply the same logic. Thus, for the second minima:

Total internal reflection is defined as the complete reflection of light rays within the same medium when passing from an optically denser medium to an optically rarer medium in such a way that the angle of incidence is greater than its critical angle.

Diaphragm or Iris: Many microscopes have a rotating disk under the stage. This diaphragm has different sized holes and is used to vary the intensity and size of the cone of light that is projected upward into the slide. There is no set rule regarding which setting to use for a particular power. Rather, the setting is a function of the transparency of the specimen, the degree of contrast you desire and the particular objective lens in use.

Diagram ofdiffractionof light

For a dark fringe, the path difference must cause destructive interference; the path difference must be out of phase by λ/2. (λ is the wavelength)

Thus, at θ = sin−1λa, there is destructive interference as any ray emanating from a point has a counterpart that causes destructive interference. Hence, a dark fringe is obtained.

For a ray emanating from any point in the slit, there exists another ray at a distance of a/2 that can cause destructive interference.

Illuminator: A steady light source (110 volts) used in place of a mirror. If your microscope has a mirror, it is used to reflect light from an external light source up through the bottom of the stage.

Applications: Compound microscopes are commonly used in fields such as biology, medicine, and research, where detailed examination of small structures is required. Other microscopes, such as stereo microscopes, are utilized for examining larger objects or conducting dissections. Electron microscopes are used for high-resolution imaging of nanoscale structures.

What isdiffractiongrating

We can consider any number of ray pairings that start from a distance a/2 from one another such as the bottom two rays in the diagram. Any arbitrary pair of rays at a distance of a/2 can be considered. We shall see the importance of this trick in a moment.

Compound microscopes and other types of microscopes differ in their design and functionality. Here are the key differences between compound microscope parts and those of other microscopes:

Remember that this is a calculation valid only if D is very large. For more details about the approximation check out our article on the Young’s Double Slit experiment.

Diffraction of light is defined as the bending of light around corners such that it spreads out and illuminates areas where a shadow is expected. In general, it is hard to separate diffraction from interference since both occur simultaneously. The silver lining which we witness in the sky is caused due to diffraction of light. When the sunlight passes through or encounters the cloud, a silver lining is seen in the sky.

Fresneldiffraction

Diffractionexamples

The phase difference is defined as the difference between any two waves or the particles having the same frequency and starting from the same point. It is expressed in degrees or radians.

Stage with Stage Clips: The flat platform where you place your slides. Stage clips hold the slides in place. If your microscope has a mechanical stage, you will be able to move the slide around by turning two knobs. One moves it left and right, the other moves it up and down.

The condition for constructive interference is that the path difference should be equal to an integral multiple of the wavelength.

Stay tuned with BYJU’S to know more about diffraction of light, refraction, reflection, interference and other related concepts with the help of interactive video lessons.

Illumination: Compound microscopes often have built-in illumination systems, such as a substage light source, condenser, and diaphragm, to provide transmitted light through the specimen. Other microscopes, like dissecting or fluorescence microscopes, may utilize different lighting techniques or illumination configurations.

Sample Size and Depth of Field: Compound microscopes are designed to observe thin, transparent specimens placed on glass slides. They offer a narrow depth of field, allowing clear focus on one plane at a time. Other microscopes, like stereo or electron microscopes, can accommodate larger specimens or samples with more depth, providing a wider depth of field.

In the single-slit diffraction experiment, we can observe the bending phenomenon of light or diffraction that causes light from a coherent source to interfere with itself and produce a distinctive pattern on the screen called the diffraction pattern. Diffraction is evident when the sources are small enough that they are relatively the size of the wavelength of light. You can see this effect in the diagram below. For large slits, the spreading out is small and generally unnoticeable.

Types ofdiffraction

Rack Stop: This is an adjustment that determines how close the objective lens can get to the slide. It is set at the factory and keeps students from cranking the high power objective lens down into the slide and breaking things. You would only need to adjust this if you were using very thin slides and you weren't able to focus on the specimen at high power. (Tip: If you are using thin slides and can't focus, rather than adjust the rack stop, place a clear glass slide under the original slide to raise it a bit higher).

Historians credit the invention of the compound microscope to the Dutch spectacle maker, Zacharias Janssen, around the year 1590 (more history here). The compound microscope uses lenses and light to enlarge the image and is also called an optical or light microscope (versus an electron microscope). The simplest optical microscope is the magnifying glass and is good to about ten times (10x) magnification.

When the double-slit in Young’s experiment is replaced by a single narrow slit, a broad pattern with a bright region at the centre is seen. On both sides of the centre, there are alternating dark and bright regions. The intensity becomes weaker away from the centre. In this article, we discuss the single slit diffraction of light in a detailed manner.

It's important to note that the term "other microscope parts" is quite broad and can include various microscope types with different designs and features. The above differences are generalized and may not apply to every microscope outside the category of compound microscopes.

Temporal coherence is known as the correlation between the field at a point and the field at the same point at a later time.