Primary laser

Outside of the occasional system calibration and model verification tests, the routine maintenance burden of a Raman system is quite low. Optical windows may need to be cleaned, though automatic window cleaning systems can be implemented if it is a known issue. The most likely maintenance activity is laser replacement. Some systems have a backup laser that turns on automatically if the primary laser fails. This lessens the impact of a failure if the unit is being used for closed-loop process control. With a quality instrument and well-developed models, process Raman installations need less maintenance than many competing techniques. 

A possible setup for the frequency measurement is depicted in Fig. 7. A frequency doubled diode laser at 972 nm is locked to the dye laser at 486 nm, which is the primary laser for driving the 1S-2S transition. A frequency comb generated by a mode locked laser is used to measure the frequency difference between the 972 nm diode laser and the 759 nm laser needed for the 2S-10S transition. Note that this experiment provides its own frequency standard, for the 1S-2S transition serves as the optical frequency reference. 

FIGURE 11.1 Top view of the crossed molecular beams machine. Shown are the main chamber, the primary (laser ablation configuration) and secondary source chambers, and the rotatable differentially pumped mass spectrometer detector. 

In order to effectively analyze the microscale heat fransfer mechmisms and to accurately model the ulfra-short pulse heating of materials, it is necess y to understand energy absorption, fransport, and storage phenomena in detail. The primary laser-sohd interaction process is the excitation of elections from their equihbriiun states to some excited states by absorption of photons. Dephasing processes take place in a very short time of about s. The occupation of these... 

Harmonics are tuneable when the primary laser radiation is obtained from a tuneable laser, such as a titanium-doped sapphire (Ti S) unit However, the need for wavelength-dependent adjustments in the CPA chain can make the tuning procedure tedious. The laser system described in Sect. 2.2 is easier to tune. Since CPA techniques are not used the entire system tunes easily together with the DFDL oscillator. The peak power is still enough for this system to generate low... 

However, since 1986, new laser schemes and applications are emerging, which push Er + to the forefront between 1987 and 1990, 600 papers have appeared dealing only with the amplification properties of Ef " (Sunak 1991). Also the replacement of broad-spectrum pumping sources (black body types) by monochromatic ones, such as a primary laser, has revived many of the older schemes which were known but not yet applied. 

Harmonics arc tunable when the primary laser radiation is obtained from a tunable laser, such as a titanimn-doped sapphire laser. However, the need for wavelength-dependent adjustments in the CPA chain can make the tuning... 

The schematic setup for the Laser Interference Experiments is shown in Fig. 5. The primary laser beam is split into two or more beams to interfere with each other on the sample surface. By the combination of a polarizer and a half-wave plate, it is possible to adjust the intensity impinging on the sample. The intensity can also be adjusted by a mechanical shutter to choose the number of pulses. By using a two-lens consisting telescope, one can change the diameter of the laser beam and therefore... 

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