Coherent Laser
A look at what is currently available on eBay
 ILX LIGHTWAVE LDX-3545 LASER DIODE DRIVER CONTROLLER BURNING COHERENT 18W OUTPUT US $100.00 
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 Coherent CO2 Silicon Si Laser Mirror Lumenis 200W US $62.00
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 COHERENT INNOVA 90 Laser Complete US $850.00
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 COHERENT ENTERPRISE II ENTCII-621 LASER HEAD AND R167-735-50 POWER SUPPLY US $6,999.99
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 Coherent Antares 76-S Yag Laser US $2,500.00
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 Coherent Enterprise ENTCIIK-DMVI Laser Head Controller P6 US $29.99
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 Coherent Laser Mirror Krypton Innova Red US $99.95
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 COHERENT 40W @40A 808nm Laser Bar Diode US $139.99
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Physics Question (10 Points)?
a) In a diode laser, electrons dropping from the conduction band, across the gap, and into the valence band produce the photons that add to the coherent light. The ZnTe laser has a band gap of 2.25 eV. Determine the wavelength of the light emitted.
b) The energy gap for Si at 300 K is 1.14 eV.
i) Find the lowest-frequency photon that will promote an electron from the valence band to the conduction band of silicon.
ii) What is the wavelength of this photon?
c) Near room temperature, an increase of I K decreases the conductivity of copper by only 0.4%. For another semiconductor, it increases the conductivity by 4.8%. Estimate the semiconductor’s band gap.
answers for b and c are
b i) 2.75 X 1014 Hz ii) 1.09 X 10-6 m c) EGAP = 0.68 eV
but I dont know how to get there
a) The relation between photon wavelength and energy is E = hc/lambda, where h = Planck's constant, c = speed of light, lambda = wavelength
Just plug in the numbers. Since E is in eV, you can use h in eV units, which is 4.14 x 10^-15 eV-s
If c is in m/sec, the wavelength will be in meters.
b) i) Instead of E = hc/lambda, use E = hf. Just plug in the values of E and h.
ii) Now you can use f = c/lambda to solve for lambda
c) I would guess there is a formula in your notes that says "relationship between conductivity temperature" that is the key to this problem.
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