1. Neodymium:YAG Laser Nd3+ in yttrium-aluminum-garnet (Y3Al5O12)
Four level laser
Powerful 1064 nm; often doubled or tripled
Pump: Kr/Ar arc lamp or flash lamp
CW or pulsed operation
Ingle and Crouch, Spectrochemical Analysis

2. Diode LASERs Conversion of electrical to optical power up to 30%.
Polished faces of semiconductor act as mirrors and reflect ≈95% of photons from leaving resonance cavity.
McCreery, R. L., Raman Spectroscopy for Chemical Analysis, 3rd ed., Wiley, New York: 2000

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

4. Semiconductor (Diode) Laser
Used in telecommunications, CD players, laser pointers etc.
Blue and UV (375 – 400 nm) diode lasers have recently been developed.
Eli Kapon, Semiconductor Lasers I, Academic Press, San Diego, 1999.

5. Semiconductor (Diode) Laser
Eugene Hecht, Optics, Addison-Wesley, Reading, MA, 1998.

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

7. He – Cd Laser
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 is propagated through the system by cataphoresis (cadmium cations are transported by discharge through the laser bore towards the cathode). Once the cadmium vapor leaves the bore region, it coalesces on any cool surface.

8. Ion Lasers (Ar+ and Kr+)
CW – pumped using an electrical discharge.
Very reliable.
Inefficient because energy is required to ionize gas.
Power up to ~40 W (distributed over many lines).
Argon ion is most common.
488 nm and 514 nm are most powerful lines.
Cluster of ~10 lines in 454 – 529 nm.
UV: 334, 352, 364 nm (need several W in visible to get ~50 mW in UV)
Deep UV: 275 nm (need W in visible to get 275 nm)

9. Excimer Lasers
Excimer is a dimer that is only stable in the excited state.
e.g. ArF+, KrF+, XeF+
Pass current through noble gas / F2 mix.
Lasing occurs as excimer returns to the ground state.
Ingle and Crouch, Spectrochemical Analysis

10. Dye Lasers Molecular transitions in the solution phase.
Active species is an organic dye (e.g. rhodamines, coumarins, fluoresceins).
To prevent overheating, a jet of the dye solution is pumped through focal point of optical system.
Broad transitions. Can be tuned over ~50 nm.
Lases in UV-Vis-IR
Difficult and expensive to operate.
Optically pumped with flashlamp or another laser.
Ingle and Crouch, Spectrochemical Analysis

11. Demtröder, W. Laser Spectroscopy, Springer, Berlin: 1996.
Dye Lasers
Demtröder, W. Laser Spectroscopy, Springer, Berlin: 1996.

12. CW Dye Laser with Second Harmonic Generation (SHG)
Ring laser with two focal points.
Ar ion laser (515 nm) for pumping.
Dyes with absorption maxima at 595 to 700 nm.
Dye jet is positioned at one focus and the second harmonic generating crystal (LiIO3) resides at the other.
Output at about 300 nm.
Cavity expansion plates allow tuning.
Myers, A.B.; Rizzo, T.R. Laser Techniques in Chemistry, Wiley, New York: 1995.

13. Dye Lasers Molecular transitions in the solution phase.
Active species is an organic dye (e.g. rhodamines, coumarins, fluoresceins).
To prevent overheating, a jet of the dye solution is pumped through focal point of optical system.
Broad transitions. Can be tuned over ~50 nm.
Lases in UV-Vis-IR
Difficult and expensive to operate.
Optically pumped with flashlamp or another laser.
Ingle and Crouch, Spectrochemical Analysis

14. Tunable Lasers E.g. Emerald laser Be3Al2Si6O18:Cr3+ (720 to 842 nm)
E.g. Titanium sapphire laser (650 to 1000 nm)
E.g. Dye lasers
E.g. Solid-state semiconductor lasers
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 panel of the laser head, rotating a prism assembly around the optical axis of the laser.

15. External Cavity Diode LASER
Diffraction grating selects and stabilizes output wavelength.
Diffraction grating permits tunability over ≈10 nm range.
Isolator reflects ≈95% of photons from diode and prevents stray light from entering resonance cavity.
McCreery, R. L., Raman Spectroscopy for Chemical Analysis, 3rd ed., Wiley, New York: 2000