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Diode Lasers What is a diode las

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Diode Lasers What is a diode las Powered By Docstoc
					                                                                 Single diode laser design
                                                          Homo-junction
                  Diode Lasers                              Single semiconductor compound (typically GaAs)
                and the Coherent Verdi V-8                  Different portions given different dopings (p-n)
                                                            Threshold current of 40,000 A/cm2
                      Andrew M.C. Dawes
                      Dean Andrew Hidas                     20% efficiency
                                                          Hetero-junction
                       Duke University
                                                            Not just one material → significant improvements
                                                            GaAlAs-GaAs typical (different bandgaps)
                                                            Threshold current 8000 A/cm2
                                                            Efficiency up to 40%
                                                          Multiple layers
                                                            Current of 1000-3000 A/cm2




       What is a diode laser?                                     How it works - in brief
Diode laser is a semiconductor device used to produce     pn junction → valence and conduction bands
a laser                                                   Electrons move to the conduction band leaving behind
Typical pn junction used in forward bias                  holes
Operation based on electrical and optical properties of   Electrons recombine with holes via stimulated emission
the material
Typical wavelengths range from visible to infrared
Small size
Common uses
  Laser pointer
  CD player
  Remote control devices




                       Small!                                               Single stripe




4 types of pumping diode lasers                                     ascii art - diode laser
                                                                       ___
Single stripe                                                        |     |           Metal case
                                                                     |     |_______________________________
Diode array                                                          |                                        \
Diode bar                                                            |       _____________________________     |
                                                                     |     |                                | |
Stacked bar                                                LD -------:===:------------------+               | |
                                                                     |     |__                  |           |__|
                                                                     |     | |___         ______|______     : :
                                                                     |     | |     |    |               |   : :
                                                           PD -------:===:----+ |<---|:::::::::::::|============> Main beam
                                                                     |     | |___|____|_____________|_ : :
                                                                     |     | Photodiode Laser diode       | :__:
                                                                     |     |\__________________________| | | Protective window
                                                          Com -------+     |           Heat sink            | |
                                                                     |     |_____________________________| |
                                                                     |                                          |
                                                                     |       _______________________________/
                                                                     |     |
                                                                     |___|
           Ideas to take home                                       808nm diodes
Diode laser is a semiconductor device (pn junction)   Strong N d : Y V O4 absorption band
Transitions occur between conduction and valence      90% of incident light is absorbed in few mm of
bands                                                 N d : Y V O4
Polished ends/mirrors = cavity                        above threshold - output power is linear with current
Single stripe, arrays, and bars                       InGaAsP on a GaAs substrate




      Verdi V-8 Laser System                                       InGaAsP/GaAs
Diode-pumped solid-state frequency doubled            Grown by Solid-source molecular beam epitaxy
Nd:Vanadate                                           (SSMBE)
   Diode-pumped                                       Aluminum free QW and waveguides
   Frequency doubled                                  Single tensile-strained quantum well (QW)
   N d : Y V O4 laser medium
                                                      Tensile strain allows shorter wavelengths
Output: ≈ 8W at 532nm.                                   energy subbands shifted
                                                         TM-polarization gain dominates TE-polarization gain




              Inside and Out                                     Diode Laser Bars
                                                      Power Conversion efficiency ≈ 50%
                                                      bandwidth ∆λ < 2.5nm
                                                      Fiber coupling > 80%spec > 90%typ
                                                      typically run at 15A → 40W




   Diode Pump Requirements                                         Fiber Coupling
High power conversion efficiency                       coupling efficiency typically > 90%
Narrow spectrum                                       each emitter → dedicated fiber
Ability to couple to fiber efficiently                  19 fibers: “wishbone configuration”




                                                                                                19
                                                                    125µm
                 Packaging                                              References II
FAP - Fiber Array Package                                 Coherent Verdi V8/V10 Operators Manual Part No.
Inside - fiber coupled 19-emitter bar                      0174-929-00 (2002)
Outside - Anode, Cathode, Fiber ports (OEM black box)     Datasheets: FAP-I, FAP-B, CCP: www.cohr.com
FAP-I integrates FAP with memory chip and temp            Coherent Technical Sales: 408-764-4294
control                                                   M. Jansen et. al. “High performance laser diode bars
                                                          with aluminum-free active regions.” Optics Express,
                                                          4:1:3-11 (1999)




                    Control
Thermo-electric coolers (TEC)
  Stabilize at factory-determined optimal temperature
  Diode 1: 24.46 C
  Diode 2: 27.43 C
  Both locked at ±0.01 C
Battery backup system
Usage/Operating statistics memory (via FAP-I)




                  Summary
Diode bars offer small-package solution to solid-state
laser pumping
Modern growth process allows stable high-power
operation ≈ 25C
Aluminum-free active area (AAA) diodes → greatly
extended lifetime
Several layers of OEM packaging → poised for market
Fiber-coupling enables turn-key application
Pricing:
   FAP-I: ≈ $6k
   FAP-B: ≈ $3-4k
   Diode Bars: ≈ $1-2k




                References I
Koechner, Walter, Solid-State Laser Engineering, 1988
Svelto, Orazio, Principles of Lasers, 1998
Yariv, Amnon, Introduction to Optical Electronics, 1976
http://members.misty.com/don/laserdio.htm
http://www.ece.concordia.ca/ i_statei/vlsi-opt/
http://www.spectraphysics.com/

				
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