Power broadening noise

Fig. 8. The 195Pt-NMR spectra of a DMF solution of [Pt2(en)3(PRI)2(N02) (N03)](N03)2 0.5 H20 (11) at 5°C, acquired on a Bruker WM-250 spectrometer operating at 53.6 MHz. (a) Power spectrum of the Fourier transform of a 1 K FID accumulated with a 5-jjls pulse width, 100-kHz spectral width, and 2000 K transients, (b and c) Normal Fourier transforms of 1 K FIDs accumulated with 10-fis pulsewidths, 42-kHz spectral width, and 64 K transients per spectrum. All FIDs were treated with 400-Hz line broadening functions to suppress noise (58).

Photoexcitation at /.e = 488 and 457.9 tim was accomplished by an Ar" " laser. An Oriel high-intensity high-pressure broadband Hg emission lamp provided the UV source. Nearly monochromatic 25 mW excitation at 353, 308, and 248 ntn was provided by 6 nm-bandwidth mirrors blazing at these wavelengths 5 mW excitation at 430, 406, and 380 nm was obtained by appropriate bandpass filters. As the ODMR signal-to-noise ratio was much poorer at these latter the microwave power was increased to up to 1400 mW. The resulting microwave field, however, was then sufficiently intense to broaden the narrow polaron resonance. Detailed descriptions of the visible- and UV-ODMR systems are given elsewhere [59,60]. 

The second contribution to the noise resulting in line broadening is due to amplitude fluctuations caused by the statistical distribution of the number of photons in the oscillating mode. At the laser output power P, the average number of photons that are transmitted per second through the output mirror i n = P/hv. With P = I mW and /zv = 2eV (= A = 600 nm), we obtain n = Sx 10. If the laser operates far above threshold, the probability p(n) that n photons are emitted per second is given by the Poisson distribution [304, 305]... 

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