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This article presents a joulemeter that permits us to measure the beam energy of a pulsed ruby laser from the HLS‐3 holographic system at the recording photosensitive surface of the holographic plate. This is an inexpensive alternative to commercially obtainable energy measuring silicon detectors. The joulemeter contains a photodiode used in the photoconductive mode, an integrating circuit, and a buffer amplifier. The output signal is displayed on the screen of a digital storage oscilloscope. We have tested the joulemeter for different photodetectors. The best responsivity, 3 V/J, was obtained with the BPW21 photodetector. Its possible to measure the energy of a different pulsed laser, by using a photodetector adapted for the laser wavelength and to change the energy domain by changing the attenuators.

The time‐resolved resonance Raman spectra of the first triplet state and the cw resonance Raman spectra of the radical cation are reported for various isotopic derivatives of the N,N,N′,N′‐tetramethyl‐p‐phenylenediamine (TMPD) and of the N,N,N′,N′‐tetraethyl‐p‐phenylenediamine (TEPD). Vibrational assignments and structural implications are discussed. The radical cation spectra are consistent with a semiquinoidal conformation of the ionized species. They are characterized by a significant frequency increase of the in‐phase ν(N–ring) mode with respect to the ground state spectra (Δν≥120 cm−1) and by the high resonance enhancement of various bands assigned to vibrations of the N(alkyl)2 groups, resulting from couplings of these vibrations with modes of the π chromophore. The triplet spectra display almost only bands due to vibrations of the N(alkyl)2 groups, implying that similar couplings take place in the T1 state. Two signals characterize the N–ring–N framework: one is assigned to the Wilson ring mode 9a ...