Femtosecond pulse generation around 650 nm in a passive mode-locked Kiton Red dye laser

Abstract

Sub 100 fs light pulses have been generated in the spectral region between 640 and 660 nm (the shortest duration being 50 fs at 653 nm) by passive mode-locking of a Kiton Red dye laser with the saturable absorber DQTCI.Nearly the whole visible and near infrared range (with some gaps) has been covered by various amplifying dye-saturable absorber combinations yielding femtosecond light pulses in cw passive or hybrid mode locked lasers [1][2][3][4]. Pulse durations below 150 fs were obtained in some of these combinations by group velocity dispersion balanced laser operation [5].In the spectral region around 650 nm sub 100 fs pulse generation has not been reported so far. The longest wavelength achieved by passive mode-locking of a Rhodamine 6G laser was 640 nm [ 6 ]. In this laser 50 fs pulses at 640 nm have been generated by the saturable absorber TCETI. Energy transfer passive mode-locking with an argon ion pump laser has been applied to cover the 652-694 nm region with Rhodamine 6G+Sulforhodamine 101 mixtures as gain medium and DQTCI or DCCI as saturable absorbers [ 7,8 ]. The shortest pulse durations obtained were 58 fs at 685 nm [8] and 120 fs at 666 nm [7]. Applying hybridly mode-locked systems pumped by the second harmonic of Nd:YAG lasers [9,10], pulses of 65 fs duration at 640 nm [9] have been obtained in a Rhodamine 6G/DODCI laser, and pulses of 60 fs duration at 675 nm were generated using Rhodamine 101 or Sulforhodamine 101 as gain media and DQTCI as absorber medium [10]. Subpicosecond Rhodamine B lasers have been operated 1 On leave from the Faculty of Physics, Sofia University, BG-1126 Sofia, Bulgaria.around 650 nm [10][11][12]. Cw passive mode-locking with DQTCI was achieved in the wavelength region of 616-658 nm [11]. However, the shortest duration was 220 fs at 635 nm [11]. Hybrid mode-locking of Rhodamin B lasers resulted in pulses of duration down to 320 fs in the spectral region between 604 and 632 nm when DQTCI or DDBCI were used as saturable absorbers [10,12]. Using Oxazine 720 as saturable absorber pulse durations down to 187 fs were obtained around 649 nm [10].Here we report on passive mode-locking of a Kiton Red laser with the saturable absorber DQTCI [13] producing sub 100 fs pulses in the wavelength region of 640-660 nm. The dyes Kiton Red 620 (Sulforhodamine B, free of sodium) [13,14] and DQTCI (1,3' -diethyl-4,2' -quinolythiacarbocyanine iodide) [13,15] were purchased from Lambda Physik. The fluorescence quantum yield of Kiton Red 620 in ethylene glycol was determined to be <P F = 0.885 ±0.015 independent of concentration up to about 5xl0~3 mol/litre. For DQTCI in ethylene glycol * F =0.049 ± 0.005 was determined giving a fluorescence lifetime of t F =20± 1 ps (radiative lifetime « 4.1 ns). The fluorescence quantum yield measurement system is described in ref. [16].Kiton Red 620 has been previously used in hybrid mode-locked systems pumped by the second harmonic of a mode-locked Nd: YAG laser, and pulses as short as 29 fs were obtained at 615 nm when a mixture of DODCI and DQOCI was use...

Concentration-dependent absorption and emission behaviour of sulforhodamine B in ethylene glycol

“…[1][2][3][4][5] and references therein). It has been applied to generate femtosecond pulses in passive mode-locked [6,7] lasers and it served as gain medium in laser amplifiers for femtosecond rhodamine 6G dye lasers [8][9][10][11].…”