Unformatted text preview: EE540 (S’ll) Homework Assignment #8 Intro to Diode Lasers. P.l of 3. The gallium arsenide (GaAs) hetero-junction diode laser oscillator in your CD player is probably
constructed as shown in the top ﬁgure of Outline 1] of our EE540 ‘Model A’ for such oscillators. We will
refer to this outline as r"‘01P” in this HW#8 Assignment, and attach it as page 3 for your convenience. 011
contains (perhaps wiih a little googling) all you will need to know to complete this assignment, in which you
- will calculate the numerical values for the most important parameters of our Model A. To calculate these
parameters, you will use the results of the experiments performed by T. Paoli on a laser he calls his ‘A laser’.
Some of these results are reproduced for you on page 2. Some are given with the following problems. (1). a) From the average mode spacing in FigHWS. 1, calculate the round—trip time my for the photons in the
TEMoo modes, and b) calculate the refractive index In for these photons. (2). Use your value for the refractive index to calculate the reﬂectivities R; = R 2 of the cavity end ‘ﬁnh'rors”.
(Each mirror is simply a dielectric/air interface.) (3). Assume that the mode at 8703A in Fig.HW8.l sees negligible gain. Calculate its natural (“passive”) decay time 1;, from its FWHM. All the modes shown in this Figure will have nearly the same passive decay
times, as explained in Fig.HW8.2 (4). Assume that the laser-mode passive decay time p, is entirely due to: a) losses out of the end mirrors,
and b) a homogeneous background absorption of ﬂ cm' in the gain region. Calculate ﬂ . (5). Paoli measured the divergence angles 6! and 3 l of the output beam of his ‘A laser’ to be 10° and 50° at currents 1' well above the threshold current 1"”, Amps. . From these measurements, calculate the width w and
depth d of the cavity mode. You may assume henceforth that the mode area A equals wd. You will notice that the symbol n; in 011 refers to the same refractive index that was symbolized by F1 in
earlier notes. Professor hopes that every other symbol in 011 has either been a) deﬁned in previously posted
notes, problems and solutions, or b) is deﬁned through its context in 011. If not, email him. ...
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- Spring '08