1 Stimulated Raman scattering If high enough powered radiation is incident on the molecule stimulated Anti-Stokes radiation can be generated.
The occurrence of Stokes emission populates E2.
This allows Anti-Stokes scattering to occur.
The stimulated Raman scattering can be used to convert fixed frequency laser output to other wavelengths. Non-linear effect used in frequency doubling crystals in many dye laser systems. 2 How a dye laser works
Laser emission from solutions of large organic dyes.
2 stagesoscillation and amplification.
Dye molecule has broad absorption and fluorescence (emission) bands.
Rhodamine B 3 How a dye laser works
Vibrational and rotational levels are a virtual continuum.
At RT most molecules in v0 of S0
Absorption follows the Franck-Condon principle.
Absorption to some v level in S1.
Vibrational relaxation to v0.
Lasing occurs from v0 to some excited vibrational level in S0.
Population inversion occurs between different vibrational (vibronic) levels.
Vibrational relaxation is energy transfer from dye molecule to the surrounding solvent. 4 How a dye laser works Oscillator
Concentrated solution of dye.
Excited by fixed frequency pump laser.
Dye molecule fluorescence is collected and dispersed using diffraction grating.
Radiation of the chosen wavelength allowed to exit the oscillator cavity
5 How a dye laser works Amplifier
One or more cells containing slightly less concentrated dye solution.
Excited by pump laser beam.
Also radiation from oscillator.
Pump laser excites dye molecules.
Beam from oscillator stimulates emission from the excited dye molecules.
6 How a dye laser works
To tune wavelength move diffraction grating in oscillator.
All computer controlled.
Change dyes to change wavelength region.
7 Rotational resolution Rotational spacings are very small require a laser with a very narrow line width.
Many lasers operate in multi-mode fashion.
Modes active in the cavity satisfy the equation
L length of cavity wavelength n integer Line profile of the laser output To reduce active modes could reduce the length of the cavity or.. 8 The use of etalons Etalon acts as a secondary cavity within the laser cavity Modes active in the cavity must satisfy resonance conditions for both the cavity and the etalon. Rotate etalon to select only a single mode. Get linewidths of lt 0.01cm-1. (very narrow) 9 Rotationally resolved spectra n-propyl benzene LIF excitation spectrum Rotational band contours Calculated conformer structures 10 Ion dip Can use to obtain ground state vibrational frequencies. 2 laser process ionisation and depletion lasers.
1st process is multi-photon ionisation - measure ion current.
2nd laser infra-red - tune through vibrational levels in S0.
When molecule absorbs v0 depopulated.
Dip observed in the ion current.
11 Ion dip N-phenyl formamide Bands in the 3400-3600cm-1 region describe the N-H and O-H stretches 12 Hole-burning Useful for untangling fluorescence or MPI spectra from different conformers. 2 laser process interogation and depletion lasers.
Depletion laser saturates electronic transition.
Fluorescence or MPI experiment carried out simultaneously.
Vibronic bands due to depleted electronic transition disappear.
Can use with ion-dip technique missing transitions show up as a dip in the ion current. 13 Hole-burning Phenylalanine 6 conformer structures - A-E and X.
PowerShow.com is a leading presentation/slideshow sharing website. Whether your application is business, how-to, education, medicine, school, church, sales, marketing, online training or just for fun, PowerShow.com is a great resource. And, best of all, most of its cool features are free and easy to use.
You can use PowerShow.com to find and download example online PowerPoint ppt presentations on just about any topic you can imagine so you can learn how to improve your own slides and presentations for free. Or use it to find and download high-quality how-to PowerPoint ppt presentations with illustrated or animated slides that will teach you how to do something new, also for free. Or use it to upload your own PowerPoint slides so you can share them with your teachers, class, students, bosses, employees, customers, potential investors or the world. Or use it to create really cool photo slideshows - with 2D and 3D transitions, animation, and your choice of music - that you can share with your Facebook friends or Google+ circles. That's all free as well!
For a small fee you can get the industry's best online privacy or publicly promote your presentations and slide shows with top rankings. But aside from that it's free. We'll even convert your presentations and slide shows into the universal Flash format with all their original multimedia glory, including animation, 2D and 3D transition effects, embedded music or other audio, or even video embedded in slides. All for free. Most of the presentations and slideshows on PowerShow.com are free to view, many are even free to download. (You can choose whether to allow people to download your original PowerPoint presentations and photo slideshows for a fee or free or not at all.) Check out PowerShow.com today - for FREE. There is truly something for everyone!