Neodymium:YAG Laser Ingle and Crouch, Spectrochemical Analysis Nd 3+ in yttrium-aluminum- garnet (Y 3 Al 5 O 12 ) Nd 3+ in yttrium-aluminum- garnet (Y

Neodymium:YAG LaserNeodymium:YAG Laser

Ingle and Crouch, Ingle and Crouch, Spectrochemical AnalysisSpectrochemical Analysis

• NdNd3+3+ in yttrium-aluminum- in yttrium-aluminum-garnet (Ygarnet (Y33AlAl55OO1212))

• Four level laserFour level laser

• Powerful line @ 1064 nm; often Powerful line @ 1064 nm; often doubled or tripleddoubled or tripled

• Pump: Kr/Ar arc lamp or flash Pump: Kr/Ar arc lamp or flash lamplamp

• CW or pulsed operationCW or pulsed operation

Diode LASERs

McCreery, R. L., McCreery, R. L., Raman Spectroscopy for Chemical Analysis, 3rd ed.Raman Spectroscopy for Chemical Analysis, 3rd ed., Wiley, New York: 2000, Wiley, New York: 2000

• Conversion of electrical to optical power up to 30%.Conversion of electrical to optical power up to 30%.

• Polished faces of semiconductor act as mirrors and reflect ≈95% of photons Polished faces of semiconductor act as mirrors and reflect ≈95% of photons from leaving resonance cavity.from leaving resonance cavity.

Stimulated Emission

Agrawal, G.P.; Dutta, N.K. Agrawal, G.P.; Dutta, N.K. Semiconductor LasersSemiconductor Lasers, Van Nostrand Reinhold, New York: 1993., Van Nostrand Reinhold, New York: 1993.

Semiconductor Semiconductor (Diode) Laser(Diode) Laser

Used in Used in telecommunications, CD telecommunications, CD players, laser pointers players, laser pointers etc.etc.

Blue and UV (375 – 400 Blue and UV (375 – 400 nm) diode lasers have nm) diode lasers have recently been recently been developed.developed.

Eli Kapon, Eli Kapon, Semiconductor Lasers ISemiconductor Lasers I, , Academic Press, San Diego, 1999.Academic Press, San Diego, 1999.

Semiconductor (Diode) LaserSemiconductor (Diode) Laser

Eugene Hecht, Eugene Hecht, OpticsOptics, Addison-Wesley, Reading, MA, 1998., Addison-Wesley, Reading, MA, 1998.

Diode LASER Output


He – Cd LaserHe – Cd Laser

www.mellesgriot.comwww.mellesgriot.com

For lasing to occur, cadmium must be heated sufficiently to obtain and maintain For lasing to occur, cadmium must be heated sufficiently to obtain and maintain the proper partial pressure of cadmium vapor in the discharge tube. The vapor the proper partial pressure of cadmium vapor in the discharge tube. The vapor is propagated through the system by cataphoresis (cadmium cations are is propagated through the system by cataphoresis (cadmium cations are transported by discharge through the laser bore towards the cathode). Once the transported by discharge through the laser bore towards the cathode). Once the cadmium vapor leaves the bore region, it coalesces on any cool surface.cadmium vapor leaves the bore region, it coalesces on any cool surface.

Ion Lasers (ArIon Lasers (Ar++ and Kr and Kr++))CW – pumped using an electrical discharge.CW – pumped using an electrical discharge.

Very reliable.Very reliable.

Inefficient because energy is required to ionize gas.Inefficient because energy is required to ionize gas.

Power up to ~40 W (distributed over many lines).Power up to ~40 W (distributed over many lines).

Argon ion is most common.Argon ion is most common.

488 nm and 514 nm are most powerful lines.488 nm and 514 nm are most powerful lines.

Cluster of ~10 lines in 454 – 529 nm.Cluster of ~10 lines in 454 – 529 nm.

UV: 334, 352, 364 nm (need several W in visible to get UV: 334, 352, 364 nm (need several W in visible to get ~50 mW in UV)~50 mW in UV)

Deep UV: 275 nm (need 20-30 W in visible to get ~10mW Deep UV: 275 nm (need 20-30 W in visible to get ~10mW @ 275 nm)@ 275 nm)

Excimer LasersExcimer Lasers

Excimer is a dimer that is only stable in the excited state.Excimer is a dimer that is only stable in the excited state.

e.g. ArFe.g. ArF++, KrF, KrF++, XeF, XeF++

Pass current through noble gas / FPass current through noble gas / F22 mix. mix.

Lasing occurs as excimer returns to the ground state.Lasing occurs as excimer returns to the ground state.


Dye LasersDye Lasers


Molecular transitions in the solution Molecular transitions in the solution phase.phase.

Active species is an organic dye (e.g. Active species is an organic dye (e.g. rhodamines, coumarins, fluoresceins). rhodamines, coumarins, fluoresceins).

To prevent overheating, a jet of the dye To prevent overheating, a jet of the dye solution is pumped through focal point solution is pumped through focal point of optical system.of optical system.

Broad transitions. Can be tuned over Broad transitions. Can be tuned over ~50 nm.~50 nm.

Lases in UV-Vis-IRLases in UV-Vis-IR

Difficult and expensive to operate.Difficult and expensive to operate.

Optically pumped with flashlamp or Optically pumped with flashlamp or another laser.another laser.


Demtröder, W. Demtröder, W. Laser Spectroscopy, Laser Spectroscopy, Springer, Berlin: 1996.Springer, Berlin: 1996.

CW Dye Laser with Second Harmonic Generation (SHG)CW Dye Laser with Second Harmonic Generation (SHG)

Myers, A.B.; Rizzo, T.R. Myers, A.B.; Rizzo, T.R. Laser Laser Techniques in Chemistry, Techniques in Chemistry, Wiley, Wiley,

New York: 1995.New York: 1995.

• Ring laser with two focal points. Ring laser with two focal points.

• Ar ion laser (515 nm) for pumping.Ar ion laser (515 nm) for pumping.

• Dyes with absorption maxima at 595 to 700 nm. Dyes with absorption maxima at 595 to 700 nm.

• Dye jet is positioned at one focus and the second harmonic generating Dye jet is positioned at one focus and the second harmonic generating crystal (LiIO crystal (LiIO33) resides at the other. ) resides at the other.

• Output at about 300 nm.Output at about 300 nm.

• Cavity expansion plates allow tuning.Cavity expansion plates allow tuning.



Molecular transitions in the solution Molecular transitions in the solution phase.phase.

Active species is an organic dye (e.g. Active species is an organic dye (e.g. rhodamines, coumarins, fluoresceins). rhodamines, coumarins, fluoresceins).

To prevent overheating, a jet of the dye To prevent overheating, a jet of the dye solution is pumped through focal point solution is pumped through focal point of optical system.of optical system.

Broad transitions. Can be tuned over Broad transitions. Can be tuned over ~50 nm.~50 nm.

Lases in UV-Vis-IRLases in UV-Vis-IR

Difficult and expensive to operate.Difficult and expensive to operate.

Optically pumped with flashlamp or Optically pumped with flashlamp or another laser.another laser.

Tunable LasersTunable Lasers

www.mellesgriot.comwww.mellesgriot.com

E.g. Emerald laser BeE.g. Emerald laser Be33AlAl22SiSi66OO1818:Cr:Cr3+ 3+ (720 to 842 nm)(720 to 842 nm)

E.g. Titanium sapphire laser (650 to 1000 nm)E.g. Titanium sapphire laser (650 to 1000 nm)

E.g. Dye lasersE.g. Dye lasers

E.g. Solid-state semiconductor lasersE.g. Solid-state semiconductor lasers

E.g. Ar/Kr ion laser: Nine selectable wavelengths (476 to 676 nm). To E.g. Ar/Kr ion laser: Nine selectable wavelengths (476 to 676 nm). To select a wavelength, the operator turns a calibrated micrometer on the back select a wavelength, the operator turns a calibrated micrometer on the back panel of the laser head, rotating a prism assembly around the optical axis panel of the laser head, rotating a prism assembly around the optical axis of the laser.of the laser.

External Cavity Diode LASER


• Diffraction grating selects and stabilizes output wavelength.Diffraction grating selects and stabilizes output wavelength.

• Diffraction grating permits tunability over ≈10 nm range.Diffraction grating permits tunability over ≈10 nm range.

• Isolator reflects ≈95% of photons from diode and prevents stray light from Isolator reflects ≈95% of photons from diode and prevents stray light from entering resonance cavity.entering resonance cavity.

Documents

Neodymium:YAG Laser Ingle and Crouch, Spectrochemical Analysis Nd 3+ in yttrium-aluminum- garnet (Y 3 Al 5 O 12 ) Nd 3+ in yttrium-aluminum- garnet (Y