ECE 476/576 Summer 1999: Final Exam

Answer all questions in the spaces provided. To obtain partial credit, all steps must be shown clearly.  Students must turn in the formula sheet brought in, with their names written on these sheets.

 

Key: Dr. Dharamsi______________________________________________

 

SSN:                           _____________________________________________

 

Pledge of Honor:        _____________________________________________

The signature required on this line signifies that the student abides by the University's Honor Pledge.

Q 1

 

 

 

 


Q1 (a)  Describe the process of Q-switching a laser

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Q 1(b) Describe the process of mode-locking a laser

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1(c)      A solid state laser consists of a host lattice, doped with a lasant, which operates at a transition corresponding to a photon energy of 2 eV. The rod is 5 cm long, having a cross sectional area of 1 cm2, and is placed in a cavity in which the mirror separation is 10 cm. The mirror reflectivities are 0.98 and 0.70, and may be assumed to be lossless (i.e. do not have any absorption). The ground state density of the dopant is 2.5 x 10 19 cm3. The stimulated emission cross section for the laser transition is 10-19 cm2. The gain medium is optically pumped by another laser in a manner that results in an initial population inversion density of 1019 cm3.  This laser is Q switched by an ideal Q-switch. Calculate the peak power and pulse width of laser pulse

 


 

 

 


 

 

 


2 (a)     Describe the process of Raman Scattering, including the difference between Stokes an AntiStokes scattering.

(b)        Discuss the process of Coherent AntiStokes Raman Scattering, including an appropriate energy level diagram as well as a block diagram of the experimental apparatus. Give examples of applications of the CARS technique.

Q3.      An optical amplifier has a length of 10 cm, a crossectional area of 1 cm2, operates on a homogeneously broadened, two-level transition, centered at 600 nm, and having a linewidth of 109 Hz.  The upper state has a spontaneous emission lifetime of 10 ns.  There exists an additional radiationless relaxation mechanism whose rate constant is108 sec-1. The pumping mechanism has established a population inversion that leads to a small signal gain of 0.2 cm-1.

 

3(a)      Calculate the output intensity in watts/cm2 when the input intensity is (Isat).

 

 


 

 

 

 

 

 

 

 

 

 

 

 

 


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


3(b)      What is the maximum power in watts that can be extracted from this amplifier?

 

Q 4(a)  Discuss homogeneous and inhomogeneous broadening, giving at least one example of each.

4(b)      Discuss Doppler Broadening and Collision Broadening.

4(c)      What are the major differences between a laser that operates on a homogeneously broadened transition and one that operates on an inhomogeneous transition?  Explain.