Saturable absorption dynamics of DODCI

Abstract

The saturable absorption dynamics of DODCI in a femtosecond dye laser is studied theoretically. The N-isomer and P-isomer photoisomerization dynamics is included. The wavelength region between 570 nm and 650 nm is considered where the N-isomer and P-isomer absorption dynamics changes from short-wavelength to longwavelength So-Si excitation. The slow saturable absorber DODCI shortens a circulating pulse in a laser oscillator down to femtosecond duration if the gain medium compensates the absorber losses. Fast local relaxation in the S 1 -state in the case of short-wavelength excitation and fast level refilling in the S^state in the case of longwavelength excitation facilitate the pulse shortening and the background signal suppression. In some papers [3, 11, 15, 16] the bleaching of the ground-state P-isomer absorption is thought to be responsible for the picosecond and femtosecond pulse generation in passively mode-locked rhodamine 6G dye lasers in the wavelength region above 600 nm. IntroductionIn this paper a detailed numerical analysis of the saturable absorption dynamics of DODCI in the wavelength region between 570 nm and 650 nm is given. The single transit of a pulse through the absorber and the repetitive passage of a pulse circulating in an oscillator are studied. The N-isomer-P-isomer photoisomerization dynamics is included [13,14]. In the long-wavelength absorption region the bleaching dynamics of the fraction of molecules interacting with the laser light is considered [17,18]. It is found that the slow saturable absorber is able to shorten nanosecond Gaussian pulses down to femtosecond pulses in multiple passages if the gain medium compensates the absorber losses. The fast relaxation of the excited Franck-Condon level in the S,-state in the case of short-wavelength excitation, and the fast spectral cross-relaxation in the S 0 -ground state in the case of

Triplet-triplet absorption of eosin Y in methanol determined by nanosecond excimer laser excitation and picosecond light continuum probing

“…For Ar L <r P the input peak intensity necessary for a certain absorption bleaching is roughly inversely proportional to the pulse duration. The medium behaves like a slow saturable absorber characterized by a saturation intensity of [ 59 ] /uLS -a h At L…”

“…The medium behaves like a fast saturable absorber with a saturation intensity of [58,59 ] AatxT is indicated by a vertical bar. The dashed curve is calculated for /CS kSo =0(^5, = 5 X10 8 s"* 1 ) and A/ L = 100 jis.…”

“…In the case of Ar L > T p the necessary input pulse energy for a fixed bleaching increases roughly linear with the pulse duration. In the case of Af L < r P (slow saturable absorption ) the saturation energy density is [ 59 ] INPUT PEAK INTENSITY L, IWcm*) Its value is indicated by a vertical bar. For A/ L > r P fast saturable absorption) the saturation energy density is given by (10) The triplet state population number density tf T (0 versus pump pulse energy density is shown in figs.…”

Generation of frequency tunable femtosecond pulses in a cw pumped linear dispersion-balanced passive mode-locked rhodamine 6G dye laser

“…The absorption cross-section spectrum and the stimulated emission cross-section spectrum of rhodamine 6G in ethylene glycol are included in fig.2 (taken from ref. [17]). …”

“…The group velocity dispersion balancing is achieved by proper adjusting the laser path through the prism-pair arrangement in the laser (prism-pair balanced operation). The saturable absorbers DODCI (3.3'-diethyloxadicarbocyanine iodide) [14], DQOCI (diethylquinoloxacarbocyanine iodide) [15]. and TCVEBI (2-[ 2-(2,3,6,7-tetra-hydro-1 H.5H-benzo [ t j ] chinolizin-9-yl) vinyl ]-3-ethylbenzothyazoIium iodide, from Delta Agency, Sofia) [5] dissolved in ethylene glycol are applied.…”