Ph. D. Photonics Q and A

1. Ministry of Higher Education and Scientific Research
University of Baghdad – College of Science
Department of Physics
FUNDAMENTALS OF PHOTONICS
Dr. Abdullah m. suhail
PH.D. postgraduate
Qahtan G. Al-zaidi
‫ﻗــــﺤﻄﺎن آﺎﻃــــــــﻊ اﻟﺰﻳــــــــﺪي‬
‫ دآﺘـــــــــــــﻮراﻩ ـــ ﻓﻴﺰﻳـــــــــﺎء‬
January 29, 2008
Fundamentals of Photonics Page 1 of 4 Wednesday, March 05, 2008
Baghdad University – College of Science – Department of Physics –Qahtan G. Al-zaidi, mobile: +009647702981421

2. Q1: In case of He‐Ne laser working in your laboratory, the red line of 632.8
is transmitted from the 3S2 to 2P4 state as shown in the spectrum figure. The
pressure is 10 torr and the distance between the electrodes is 20 cm.
Determine the following:
1. The operational voltage
2. The small signal gain coefficient
3. The required pumping rate
For Helium – Neon laser, the following data can both be extracted from the energy – level
diagram and the literature:
The spontaneous lifetime . 0.7
The transition line width ∆ 1.5
The transition cross section 1 10
I. The operational voltage for laboratory He‐Ne laser is ℓ
Where:
26.6
.
Thus:
26.6 20 10 5320 5.32
II. The small signal gain coefficient . . 4 .
.
Here, .
.
Where:
. ln ln 0.07615
ℓ .
Therefore, the threshold population inversion would be:
0.07615
. 7.6148 10
1 10
The small signal gain coefficient . 4 . 1 10 4 7.6148 10
0.30459
.
III. The required pumping rate
.
0.07615
1.0878 10 ·
0.7 10 1 10
Q2: For semiconductor laser the injected carrier concentration at balance between
emission and absorption Δ 1.25 10 . For ∆ the injected carrier
concentration near the operating point is equal to ∆ 1.4 ∆ and the
absorption coefficient 600 . Find the peak gain coefficient of such
laser. If the crystal length 350 , find the total gain.
Fundamentals of Photonics Page 2 of 4 Wednesday, March 05, 2008
Baghdad University – College of Science – Department of Physics –Qahtan G. Al-zaidi, mobile: +009647702981421

3. ‫اﻟﺤﻴـــــﻮد ﻣــــــــﻦ ﺷـــــــﻖ ﻣﻨﻔــــﺮد وﺗﺤﻘﻴـــــــﻖ ﻣﺒـــــﺪأ اﻟﻼدﻗــــــﺔ ﻟـ هﺎﻳﺰﻧﺒــــﺮك‬
‫1. ﻣﺎ ﺳﻠﻮك اﻟﻀﻮء ﻓﻲ ﺗﺠﺮﺑﺔ اﻟﺤﻴﻮد ﻣﻦ ﺷﻖ ﻣﻨﻔﺮد ؟ ﻟﻤﺎذا ؟ اذآﺮ ﻇﻮاهﺮ ﺑﺼﺮیﺔ یﺴﻠﻚ ﻓﻴﻬﺎ اﻟﻀﻮء اﻟﺴﻠﻮك ﻥﻔﺴﻪ .‬
‫اﻟﺴﻠﻮك ﻣﻮﺝﻲ ﻷن ﻇﻮاهﺮ ﺑﺼﺮیﺔ آﺎﻟﺤﻴﻮد ، اﻟﺘﺪاﺧﻞ ، اﻻﺳﺘﻘﻄﺎب ﻻ یﻤﻜﻦ أن ﺗﻔﺴﺮ أذا اﻋﺘﺒﺮ اﻟﻀﻮء ﺳﻠﺴﺔ ﻣﻦ‬
‫اﻟﻔﻮﺗﻮﻥﺎت ‪. Photons‬‬
‫2. ارﺳﻢ داﻟﺔ اﻟﺸﺪة ﻟﻠﺤﻴﻮد ﻣﻦ ﺷﻖ ﻣﻨﻔﺮد ﻋﺮﺽﻪ ‪ . d‬ﻣﺎ اﻟﻘﻴﺎس اﻟﺰاوي ) ‪ ( Angular Size‬ﻟﻠﺸﺪة اﻟﻌﻈﻤﻰ اﻻﺳﺎﺳﻴﺔ ؟‬
‫ ‪Sinθ Angular Size‬‬
‫‪β‬‬ ‫ ‬ ‫ ‬ ‫ ‬ ‫ ‬
‫/‬
‫ ‬ ‫ ‬ ‫ ‬ ‫ ‬ ‫:‬
‫ ‬ ‫ ‬
‫ ‪Central‬‬
‫ ‪Thus, the angular size of the central principal maximum‬‬
‫ ‪principal‬‬
‫ :‪ is‬‬ ‫ ‪maximum‬‬
‫ ‬
‫ ‬
‫ ‬ ‫ ‪Secondary principal‬‬
‫ ‬
‫ ‬ ‫‪maximum‬‬
‫ 3‐‬ ‫ 2‐‬ ‫ 1‐‬ ‫ 0‬ ‫ 1‬ ‫ 2‬ ‫ 3‬ ‫ ‪n‬‬
‫ ‬ ‫ ‬ ‫ ‬ ‫ ‬ ‫‪β‬‬
‫3. هﻞ ان ﺝﻤﻴﻊ اهﺪاب اﻟﺤﻴﻮد ﻣﻦ ﺷﻖ ﻣﻨﻔﺮد ﻟﻬﺎ ﻥﻔﺲ ﺗﻮزیﻊ اﻟﺸﺪة ؟ ﻟﻤﺎذا ؟‬
‫آﻼ ، ﺗﺘﺮآﺰ اﻟﺸﺪة ﻓﻲ اﻟﻬﺪب اﻟﻤﺮآﺰي )اﻟﺸﺪة اﻟﻌﻈﻤﻰ اﻷﺳﺎﺳﻴﺔ( وﺗﺒﺪأ اﻟﺸﺪة ﺑﺎﻷﻥﺨﻔﺎض ﺗﺪریﺠﻴﺎ ً ﻓﻲ اهﺪاب اﻟﺤﻴﻮد‬
‫ﻋﻠﻰ ﺝﺎﻥﺒﻲ اﻟﺸﺪة اﻟﻌﻈﻤﻰ اﻻﺳﺎﺳﻴﺔ وﻓﻘﺎ ًﻟﻠﻌﻼﻗﺔ اﻟﺮیﺎﺽﻴﺔ :‬
‫4. هﻞ ان ﻣﺎ ﺗﺮاﻩ ﻣﻦ اهﺪاب یﻤﺜﻞ ﺷﺪة اﻻﻣﻮاج اﻟﺜﺎﻥﻮیﺔ اﻟﻤﺘﺪاﺧﻠﺔ ام ﺳﻌﺘﻬﺎ ؟ ﻟﻤﺎذا ؟‬
‫ﺷﺪة اﻻﻣﻮاج اﻟﺜﺎﻥﻮیﺔ وﻟﻴﺴﺖ ﺳﻌﺘﻬﺎ .‬
‫5. ﻣﺎذا یﺤﺼﻞ ﻟﻨﻤﻂ اﻟﺤﻴﻮد ﻣﻦ ﺷﻖ ﻣﻨﻔﺮد ) ﻋﺮض اﻟﺸﺪات اﻟﻌﻈﻤﻰ اﻻﺳﺎﺳﻴﻪ واﻟﺜﺎﻥﻮیﻪ واﻟﻤﺴﺎﻓﻪ‬
‫اﻟﻔﺎﺹﻠﻪ ﺑﻴﻨﻬﺎ ( ﻋﻨﺪ : 1 زیﺎدة اﻟﻤﺴﺎﻓﻪ ﺑﻴﻦ اﻟﺸﺎﺷﻪ واﻟﺸﻖ اﻟﻤﻨﻔﺮد 2 ﻥﻘﺼﺎن ﻋﺮض اﻟﺸﻖ اﻟﻤﻨﻔﺮد‬
‫3 اﺳﺘﺨﺪام ﺽﻮء ﻟﻴــﺰر اﻻرﮔـــــــــﻮن )‪ .(λ=514 nm‬اذآﺮ اﻟﻌﻼﻗﺎت اﻟﺮیﺎﺽﻴﻪ اﻟﻤﻨﺎﺳﺒﻪ .‬
‫اﻟﻌﻼﻗﺔ اﻟﺮیﺎﺽﻴﺔ :‬
‫‪Fundamentals of Photonics‬‬ ‫4 ‪Page 3 of‬‬ ‫8002 ,50 ‪Wednesday, March‬‬
‫124189207746900+ :‪Baghdad University – College of Science – Department of Physics –Qahtan G. Al-zaidi, mobile‬‬
‫ ‬

4. ‫زیﺎدة ‪ b‬ﺡﺴﺐ اﻟﻌﻼﻗﺔ اﻋﻼﻩ ﺗﺴﺒﺐ زیﺎدة ﻋﺮض اﻟﺸﺪات اﻟﻌﻈﻤﻰ اﻻﺳﺎﺳﻴﺔ واﻟﺜﺎﻥﻮیﺔ وزیﺎدة اﻟﻤﺴﺎﻓﺔ اﻟﻔﺎﺹﻠﺔ‬
‫ﺑﻴﻨﻬﺎ .‬
‫ﻥﻘﺼﺎن ‪ d‬یﺴﺒﺐ زیﺎدة ﻋﺮض اﻟﺸﺪات اﻟﻌﻈﻤﻰ اﻻﺳﺎﺳﻴﺔ واﻟﺜﺎﻥﻮیﺔ وزیﺎدة اﻟﻤﺴﺎﻓﺔ اﻟﻔﺎﺹﻠﺔ ﺑﻴﻨﻬﺎ .‬
‫أﺳﺘﺨﺪام ﻟﻴﺰر اﻵرﮔون یﺴﺒﺐ ﻥﻘﺼﺎن ﻋﺮض اﻟﺸﺪات اﻟﻌﻈﻤﻰ اﻻﺳﺎﺳﻴﺔ واﻟﺜﺎﻥﻮیﺔ وزیﺎدة اﻟﻤﺴﺎﻓﺔ اﻟﻔﺎﺹﻠﺔ ﺑﻴﻨﻬﺎ‬
‫.‬
‫6. آﻢ ﻋﺪد اﻟﺸﺪات اﻟﻌﻈﻤﻰ واﻟﺼﻐﺮى ) ‪ ( Intensity Maxima And Minima‬ﻟﻠﺘﺪاﺧﻞ اﻟﺘﻲ ﺗﻮﺝﺪ‬
‫داﺧﻞ ﻏﻼف اﻟﺤﻴـــــﻮد ) اﻟﻬﺪب اﻟﻤﺮآﺰي ﻟﻠﺤﻴﻮد ( اﻟﺬي یﻮﻟﺪﻩ ﻣﺤﺰز ﻋﺪد ﺡﺰوزﻩ ‪ 6 L/mm‬؟‬
‫وﺽﺢ ﺑﺎﻟﺮﺳﻢ .‬
‫یﻮﺝﺪ ﻋﺪد 4=2-‪ N‬ﻣﻦ اﻟﺸﺪات اﻟﻌﻈﻤﻰ اﻟﺜﺎﻥﻮیﺔ ﺑﻴﻦ آﻞ ﺷﺪﺗﻴﻦ ﻣﻦ اﻟﺸﺪات اﻟﻌﻈﻤﻰ اﻻﺳﺎﺳﻴﺔ داﺧﻞ ﻏﻼف اﻟﺤﻴﻮد‬
‫اﻟﻨﺎﺗﺞ ﻣﻦ اﻟﻤﺤﺰز وﻋﺪد 5=1-‪ N‬ﻣﻦ اﻟﺸﺪات اﻟﺼﻐﺮى داﺧﻞ ﻏﻼف اﻟﺤﻴﻮد ﻥﻔﺴﻪ .‬
‫7. ﻣﺎ اﻟﺠﺴﻴﻤﺔ اﻟﺘﻲ ﺗﻢ ﺗﻄﺒﻴﻖ ﻣﺒﺪأ اﻟﻼدﻗﺔ ﻟـ هﺎیﺰﻥﺒﺮگ ﻋﻠﻴﻬﺎ ؟ أذآﺮ اﻟﻌﻼﻗﺔ اﻟﺮیﺎﺽﻴﺔ ﻟﻬﺬا اﻟﻤﺒﺪأ.‬
‫∆. ∆‬ ‫اﻟﻔﻮﺗــــــﻮن . اﻟﻌﻼﻗــﺔ اﻟﺮیﺎﺽﻴﺔ :‬
‫ﻗﻴــــﺎس ﻣﻌﺎﻣـــــﻞ أﻥﻜﺴـــــﺎر ﺷﺮیﺤــــﺔ زﺝﺎﺝﻴـــﺔ ﺷﻔﺎﻓــــﺔ ﺑﺎﺳﺘﺨــﺪام ﻣﻘﻴﺎس اﻟﺘﺪاﺧــﻞ ﻟـ‬
‫ﻣﺎیﻜﻠﺴــﻦ‬
‫1. ﻣﺎ هﻮ ﻣﻌﺎﻣﻞ اﻻﻥﻜﺴﺎر؟ ﻣﺎ ﺗﺄﺙﻴﺮ زیﺎدة ﺳﻤﻚ اﻟﺸﺮیﺤﻪ اﻟﺰﺝﺎﺝﻴﻪ ﻋﻠﻰ ﻋﺪد اﻟﺤﻠﻘﺎت اﻟﺘﻲ ﺗﺰاح ﻋﻨﺪ دوران اﻟﺸﺮیﺤﻪ ؟‬
‫اﻟﻨﺴﺒﺔ ﺑﻴﻦ ﺳﺮﻋﺔ اﻟﻀﻮء ﻓﻲ اﻟﻔﺮاغ اﻟﻰ ﺳﺮﻋﺘﻪ ﻓﻲ اﻟﻮﺳﻂ وهﻮ آﻤﻴﺔ ﻋﺪیﻤﺔ اﻟﻮﺡﺪات . ریﺎﺽﻴﺎ ً:‬
‫زیﺎدة ﺳﻤﻚ اﻟﺸﺮیﺤﺔ یﺴﺒﺐ زیﺎدة ﻋﺪد اﻟﺤﻠﻘﺎت اﻟﻤﺰاﺡﺔ ﻣﻦ ﻣﺮآﺰ اﻟﻨﻤﻂ اﻟﻬﺪﺑﻲ اﻟﺤﻠﻘﻲ ﺡﺴﺐ اﻟﻌﻼﻗﺔ اﻟﺮیﺎﺽﻴﺔ :‬
‫ﺡﻴﺚ ‪ δ‬یﻤﺜﻞ ﻓﺮق اﻟﻤﺴﺎر اﻟﺒﺼﺮي اﻟﻤﻀﺎف اﻟﻰ ﻓﺮق اﻟﻤﺴﺎر اﻟﺒﺼﺮي اﻟﻜﻠﻲ ﺑﻴﻦ اﻟﺸﻌﺎﻋﻴﻦ اﻟﻤﻮﻟﺪیﻦ ﻟﻨﻤﻂ اﻟﺘﺪاﺧﻞ ، ‪t‬‬
‫یﻤﺜﻞ ﺳﻤﻚ اﻟﺸﺮیﺤﺔ اﻟﻤﻌﺘﺮﺽﺔ ﻟﻤﺴﺎر اﻟﺸﻌﺎع اﻟﻤﺘﺠﻪ ﻟﻠﻤﺮﺁة 1‪ M‬و‪ n‬ﻣﻌﺎﻣﻞ أﻥﻜﺴﺎرهﺎ ، ‪ m‬یﻤﺜﻞ ﻋﺪد اﻟﺤﻠﻘﺎت اﻟﻤﻈﻠﻤﺔ‬
‫اﻟﺘﻲ ﺗﻌﺘﺮض ﻣﺠﺎل اﻟﺮؤیﺎ )ﺗﺨﺘﻔﻲ ﻓﻲ اﻟﻤﺮآﺰ(ﻋﻨﺪ ﺗﺪویﺮ اﻟﺸﺮیﺤﺔ و ‪ λ‬اﻟﻄﻮل اﻟﻤﻮﺝﻲ ﻟﻠﻀﻮء اﻟﻤﺴﺘﺨﺪم .‬
‫وﺝﺪیﺮٌ ﺑﺎﻷﺷﺎرة أن زیﺎدة ﺳﻤﻚ اﻟﺸﺮیﺤﺔ ﻻ یﺆﺙﺮ ﻋﻠﻰ ﻗﻴﻤﺔ ﻣﻌﺎﻣﻞ اﻻﻥﻜﺴﺎر.‬
‫2. ﻣﺎ ﺳﺒﺐ آﻮن اهﺪاب اﻟﺘﺪاﺧﻞ ﻓﻲ ﻣﻘﻴﺎس اﻟﺘﺪاﺧﻞ ﻟﻤﺎیﻜﻠﺴﻦ ﺑﺸﻜﻞ ﺡﻠﻘﺎت داﺋﺮیﻪ ﻣﺘﻤﺮآﺰﻩ ؟ ﻣﺎ ﺳﺒﺐ ﻇﻬﻮرهﺎ ﺧﻼف‬
‫ذﻟﻚ اﺡﻴﺎﻥﺎ ؟ ﻋﺰز اﺝﺎﺑﺘﻚ ﺑﺬآﺮ اﻟﻌﻼﻗﻪ اﻟﺮیﺎﺽﻴﻪ اﻟﻤﻨﺎﺳﺒﻪ .‬
‫ﻷن اﻟﻤﺤﻞ اﻟﻬﻨﺪﺳﻲ ﻟﻠﻨﻘﺎط اﻟﻤﺘﺴﺎویﺔ ﻓﺮق اﻟﻄﻮر اﻟﻜﻠﻲ ﺑﻴﻦ اﻟﺸﻌﺎﻋﻴﻦ اﻟﻤﻮﻟﺪیﻦ ﻟﻨﻤﻂ اﻟﺘﺪاﺧﻞ یﻜﻮن ﻋﻠﻰ ﺷﻜﻞ داﺋﺮة .‬
‫اﻟﻌﻼﻗﺔ اﻟﺮیﺎﺽﻴﺔ :‬
‫3. هﻞ یﻤﻜﻦ اﺝﺮاء اﻟﺘﺠﺮﺑﻪ ﺑﺎﺳﺘﺨﺪام ﺽﻮء ﻣﺘﻌﺪد اﻻﻟﻮان ؟ آﻴﻒ ﺳﻴﻜﻮن ﺷﻜﻞ اﻻهــﺪاب ان ﺗﻜﻮﻥﺖ ؟ ﻟﻤﺎذا ؟‬
‫ﻥﻌﻢ ویﻜﻮن ﺷﻜﻞ اﻻهﺪاب ﻓﻲ ﻥﻤﻂ اﻟﺘﺪاﺧﻞ ﺡﻠﻘﺎت ﻣﻠﻮﻥﺔ ﻣﺘﻤﺮآﺰة . اﻟﺒﻘﻌﺔ اﻟﻤﺮآﺰیﺔ ﻟﻨﻤﻂ اﻟﺘﺪاﺧﻞ ﺗﻜﻮن ﻣﻈﻠﻤﺔ ذات‬
‫ﺡﺎﻓﺎت ﻣﻠﻮﻥﺔ . اﻟﻌﻼﻗﺔ اﻟﺮیﺎﺽﻴﺔ :‬
‫‪Fundamentals of Photonics‬‬ ‫4 ‪Page 4 of‬‬ ‫8002 ,50 ‪Wednesday, March‬‬
‫124189207746900+ :‪Baghdad University – College of Science – Department of Physics –Qahtan G. Al-zaidi, mobile‬‬
‫ ‬

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