Frequency-doubling techniques

Constraints for the use of DLs in AAS arise from their limited availability with emission wavelengths in the range 190—315 nm, which is also inaccessible with frequency doubling techniques. This however will most likely not remain a fundamental limitation, as the development of short wavelength diode lasers is driven by the telecommunication and electronics industry. 

There are, firstly, the improvement of frequency-doubling techniques in external cavities, the realization of more reliable cw-parametric oscillators with large output power, and the development of tunable narrow-band UV sources, which have expanded the possible applications of coherent light sources in molecular spectroscopy. Furthermore, new sensitive detection techniques for the analysis of small molecular concentrations or for the measurement of weak transitions, such as overtone transitions in molecules, could be realized. Examples are Cavity Ringdown Spectroscopy, which allows the measurement of absolute absorption coefficients with great sensitivity or specific modulation techniques that push the minimum detectable absorption coefficient down to 10 " cm ... 

The experimental configuration of the pump-probe experiment is similar to Ref. [5]. A home built non-collinear optical parametric amplifier (nc-OPA) was used as a pump, providing Fourier-transform-limited 30 fs pulses, which could be spectrally tuned between 480-560 nm. In all experiments white-light generated in a sapphire crystal using part of the fundamental laser (800 nm), was used as probe light. In the pump-probe experiments the pump was tuned to the S2 0-0 band for carotenoids with n>l 1. In the case of M9, it was not possible to tune the nc-OPA to its 0-0 transition, and hence another nc-OPA tuned to 900 nm was frequency doubled and used for excitation. In addition to conventional transient absorption pump-probe measurements, we introduce pump-deplete-probe spectroscopy, which is sensitive to the function of an absorbing state within the deactivation network. In this technique, we... 

HO measurement techniques in the troposphere are the principal focus of this chapter. All reported fluorescence measurements of HO in the troposphere have used lasers. Most of the early tropospheric laser fluorescence work used a frequency-doubled Nd.YAG laser to pump a Rh6G dye laser that was also frequency-doubled and tuned to either the Px( 1) line or the QiU + R23 line group of the A2 v = l X2 v" = 0 band of HO at 282 nm. Fluorescence is detected from the A2X v = 0 —> X2 v" = 0 band at 309 nm. Although the three groups to report tropospheric HO data by this method have often used similar lasers and have usually pumped the same transitions, the air sampling configurations have been quite different. 

The theory and instrumentation of Fourier transform mass spectrometry (FTMS) have been discussed extensively in this book and elsewhere [21-23]. All experiments were performed on a Nicolet prototype FTMS-1000 Fourier transform mass spectrometer previously described in detail [24] and equipped with a 5.2 cm cubic trapping cell situated between the poles of a Varian 15 in. electromagnet maintained at 0.85 T. The cell was constructed in our laboratory and utilizes two 80 transmittance stainless steel screens as the transmitter plates. This permits irradiation with a 2.5 kW Hg-Xe arc lamp, used in conjunction with a Schoeffel 0.25 m monochromator set for 10 nm resolution. Metal ions are generated by focusing the beam of a Quanta Ray Nd YAG laser (either the fundamental line at 1064 nm or the frequency doubled line at 532 nm) into the center-drilled hole (1 mm) of a high-purity rod of the appropriate metal supported on the transmitter screen nearest to the laser. The laser ionization technique for generating metal ions has been outlined elsewhere [25]-... 

Reviews addressing specifically poled polymers for frequency doubling of a laser diode have been published emphasizing the different material aspects and potential phase matching techniques [9]. The best materials available at that time were also reviewed. There has also been a more general, recent review specifically concerned with the work performed in Japan and addressing the question of materials and phase-matching techniques [10]. 

In conclusion we presented an absolute frequency measurement and a frequency comparison of two iodine stabilized frequency-doubled Nd YAG laser systems, one set up at the Institute of Laser Physics, Novosibirsk, Russia, the other at the Physikalisch-Technische Bundesanstalt, Braunschweig, Germany. The individual frequency stability and the reproducibility of the two laser systems were characterized. It was found that despite fundamental differences as far as frequency generation, signal detection and frequency stabilization techniques are concerned the combined frequency reproducibility of the two laser systems was better than 1.5 0.7 kHz. In a further experiment the absolute frequencies of HFS components of the R(56)32-0 and P(54)32-0 transitions in I2 were determined using a phase-coherent frequency chain. This chain links the frequency of the -stabilized Nd YAG laser to a CH4-stabilized He-Ne laser at 3.39 pm. The He-Ne reference was calibrated before the measurement against an atomic... 

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