Tuning of lasers

An interesting feature of our experimental scheme is that it could also be used for the 6Li isotope. Since the resonance spectra of both isotopes of lithium are not very different, one would only need a small change in the tuning of lasers. Comparison between 7Li and 6Li results would then provide an independent limit on neutron charge. 

Lateral resolution. When brilliant light sources like lasers or synchrotron radiation are used, the lateral resolution typically is diflractirMi limited in the range of a few micrometers for IR microscopy [2,11]. This can be improved by orders of magnitude with near-held IR microscopy [12], which enables resolution down to a few tens of nanometers, and spectroscopic studies by tuning of lasers [18] or use of a broadband synchrotron or laser source. IRSE biochip characterization with lateral resolution down to approximately 200 X 400 pm is possible. 

Fig. 5.56a,b. Discontinuous tuning of lasers (a) part of the neon spectrum excited by a single-mode dye laser in a gas discharge with Doppler-limited resolution, which conceals the cavity mode hops of the laser (b) excitation of Na2 lines in a weakly collimated beam by a single-mode argon laser. In both cases the intracavity etalon was continuously tilted but the cavity length was kept constant... 

Despite the fact that the first laser to be produced (the ruby laser. Section 9.2.1) has the remarkable property of having all its power concentrated into one or two wavelengths, a property possessed by most lasers, it was soon realized that the inability to change these wavelengths appreciably, that is to tune the laser, is a serious drawback which limits the range of possible applications. 

Laser Photochemistry. Photochemical appHcations of lasers generally employ tunable lasers which can be tuned to a specific absorption resonance of an atom or molecule (see Photochemical technology). Examples include the tunable dye laser in the ultraviolet, visible, and near-infrared portions of the spectmm the titanium-doped sapphire, Tfsapphire, laser in the visible and near infrared optical parametric oscillators in the visible and infrared and Line-tunable carbon dioxide lasers, which can be tuned with a wavelength-selective element to any of a large number of closely spaced lines in the infrared near 10 ]lni. 

Because of the narrow line width, absorption of laser energy can excite one specific state in an atom or molecule. The laser is tuned so that its wavelength matches an absorption corresponding to the desired state, which may be an electronic state or vibrational state. Absorption of laser energy can lead to excitation of specified states much more effectively than absorption of light from conventional light sources. 

Both the modes of operation described in Sect. 5.2 may be used for the detection of chemicals in liquid solution. Because the analyte s absorption line width is very broad, overlapping several (or many) WGMs, no tuning of the microresonator, or locking of a WGM to the scanning laser is necessary. In fact, a broadband source such as a light-emitting diode (LED) may be used. 

In optical tweezer experiments, the optical scattering force is used to trap particles, but the force can also be used to control the shape of liquid droplets26. An infrared laser with 43-mW power focused onto a microdroplet on a superhydrophobic surface enabled up to 40% reversible tuning of the equatorial diameter of the droplet26. Such effects must naturally also be taken into account when exciting laser modes in droplets in experiments with levitated drops. 

Tunable coherent light sources can be realized in several ways. One possibility is to make use of lasers that offer a large spectral gain profile. In this case, wavelength-selecting elements inside the laser resonator restrict the laser oscillation to a narrow spectral interval and the laser wavelength may be continuously tuned across the gain profile. Examples of this type of tunable laser are the dye lasers were treated in the previous section. 

Therefore, it is clear that different frequency conversion processes, together with the variety of lasers, have led to a great variety of coherent sources with large and differing tuning ranges. The whole spectral range of 185-3400 nm can be covered by different methods. 

Tunability of the blue light from 418 mn to 429 mn was also possible, via simple tuning of the CnLiSAF pump laser. This 11 nm tuning range eoineides with the fundamental aeeeptanee bandwidth of 11 nm for whieh the appKTP waveguide was designed. 

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