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Agenda

Agenda. Review from last class Aside: application of chirped optical pulses EM waves in a waveguide: telecommunications Real optical communications systems Detector technology Optical design – question 5b). M.E.: 16.6 “Lasers” Siegman. Aside: Problem set 2 -Tuesday.

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Agenda

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  1. Agenda • Review from last class • Aside: application of chirped optical pulses • EM waves in a waveguide: telecommunications • Real optical communications systems • Detector technology • Optical design – question 5b) M.E.: 16.6 “Lasers” Siegman Aside: Problem set 2 -Tuesday. MIDTERM: 26 October 2004 7PM-8:30PM Location: Stirling412A and 412B Laser Optics – Phys460

  2. z 1. Review: chirped pulses Gaussian pulse duration Dispersion length Instantaneous frequency Peak of envelope: I should have been more careful: E() does change as a function of z. but frequency content CONSTANT (i.e., Abs[E()] constant) Laser Optics – Phys460

  3. Heme group with C0 attached to iron Energy vibrational levels Interatomic distance between C and O 2. Aside: application of chirped pulses • Unconventional control in a biological system Fe Laser Optics – Phys460

  4. 2. Aside, cont.: the experiment “unchirped” optical pulse HbCO IR pump IR probe Spectrometer Laser Optics – Phys460

  5. s43 s32 s21 s10 2. Aside, cont.: results  [wavenumber] 3E10cm/s =  [Hz] What absorption do I have due to 3->4 transition if: -no population in levels 3 and 4? -level 3 populated and no population in 4? Laser Optics – Phys460

  6. 3. Real world telecom: WDM Each channel a different “colour” INPUT time Real world: wavelength division multiplexing Coarse WDM: 20nm spacing Dense WDM: 100GHz spacing nm Laser Optics – Phys460

  7. 3. Telecom, detection WDM makes detection much easier: Passive wavelength selective filter time time time Laser Optics – Phys460

  8. 3. Telecom, detection • General detector technology • photovoltaic (photodiode, avalanche photodiode) • photomultiplier • photoconductor • thermal detectors (far infrared) • Issues for detection • “Dark” signal (noise equivalent power) • Quantum efficiency • Responsivity • Linearity • Speed • Ease of use 200nm-15m 200nm-1100nm 2-10m >1m Laser Optics – Phys460

  9.  z z z<0 z=0 4. Optical design – question 5b) • Each different “beam” has its own z coordinate system, with beam propagating in +z direction • Negative radius of curvature of a beam means a converging beam • Determine question requirements: • beam waist at 100m • small spot size z=0 z<0 Laser Optics – Phys460

  10. 4. Optical design: break down the problem • What do you know? balloon Unknown optical system Laser: 500nm 100m Divergence angle: 0.5mrad Spot size: 2mm Sets q input! Need biggest possible optics at output of optical system! AND R=-100m Laser Optics – Phys460

  11. 4. Optical design, cont. • Pick final optic! Unknown optical system Laser: 500nm R=Rin w=2mm R=-100m w=[optic diameter]/4 d1 d2 Laser Optics – Phys460

  12. 4. Optical design, cont. • If you can use ray optics, use ray optics (have to make sure z>>z0) • All rays transform by the same ABCD matrix. The most convenient ray to consider is the ray positioned w from the z-axis, since we can easily write its slope from R. • Can easily “convert” back to q parameter if we need to model as a Gaussian beam r’ R w R z r’=w/R assuming z>z0 Laser Optics – Phys460

  13. 4. Optical design, cont. • Check that z>>z0 throughout system Laser: 500nm R=Rin w=2mm R=-100m w=[optic diameter]/4 d1 d2 Laser Optics – Phys460

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