Optoelectronics- practice questions /X Define the three main light-matter proces

Question

Optoelectronics- practice questions /X Define the three main light-matter processes and for each one give an example of a real device that makes use of that particular light-matter interaction Define population inversion and explain how it is usually obtained and Q-| how it relates to the optical gain.) ? 3. How does the cavity design of a semiconductor laser affect device erformance? 32 4. Why is the thickness of the intrinsic layer much greater than that of the P. or N-type layers of a PIN Photodiode? 2 . Define the terms population inversion, ontical aain an6 threshold gain as applied to discrete energy level lasers. Define the terms spontaneous emission, stimulated emission and stimiulated absorption. In each case, illustrate your answer using an energy level diagram for a two level discrete energy system. what laser output characteristics do the Longitudinal and Transverse Modes influence?2 8. Sketch the Light Current curve of à typical semiconductor laser and identify the dominant physical process in each region. 1 9. Explain how population inversion is obtained in both 3-level and 4-level discrete energy laser systems. Which system is likely to have the lower lasing threshold and why? Ielnu ot two rueadet 10.State the two round-trip conditions that must be satisfed in order to obtain stable lasing operation. 11. What are the three main light-matter interactions that take place at room temperature, which of these processes dominates the light emission process in (i) a LED and (ii) a LASER?

Explanation / Answer

1) 3 main light matter processes:

-> emission: it is a phenomenon of excitation of atoms/ molecules of matter of higher intensity but decays and the light that emits out of the matter is of lower intensity.

Eg. Epifluorence microscope. It excites a fluor molecule with a certain wavelength and the emitted higher wavelength light is detected. It helps to detect the presence or localisation of that particular fluor / fluor tagged entity.

-> absorption : it is the process in which matter uses/absorbs some amount of light incident to it.

Eg. Sunglasses - they absorbs the harmful UV light and allows low light intensity to the eyes preventing damage to them.

-> scattering : the incident light is deflected to different angles by opaque objects without any change in the intensity of light.

Eg. An LED panel used to form artificial sunlight ( recent research). It uses the scattering of incident light by nano particles present in the panel.

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