Passive Q-switching and mode-locking for the generation of nanosecond to femtosecond pulses

Abstract

Abstract. The passive and hybrid Q-switching and mode-locking of solid-state lasers, dye lasers, semiconductor lasers and gas lasers is reviewed. The dynamics of saturable absorbers and reverse saturable absorbers is illustrated. The nanosecond pulse generation by passive and hybrid Q-switching of low-gain active media is described. The picosecond and femtosecond pulse generation by passive and hybrid mode-locking in low-gain and highgain active media is analysed. The performance data of passively and hybridly mode-locked cw femtosecond dye lasers are collected. The pulse shortening of ultra-fast pulses with saturable absorbers in intra-cavity and extra-cavity configurations is discussed. PACS: 42.55The photonic switching of lasers provides an important technique to generate short light pulses in the nanosecond to femtosecond time regime. The photons generated in the laser modify the transmission of the switching elements and cause the formation of short pulses. Saturable absorbers serve as intensity or energy dependent coupling elements in most cases. But occasionally intensity and energy-dependent refractive index changes have been applied. Nanosecond light pulses are generated in passively Q-switched lasers. The passive mode-locking of laser leads to the generation of nanosecond, picosecond or femtosecond pulse trains. The actual pulse durations depend on the spectroscopic data of the active media and of the passive elements.The nonlinear response of absorbers to light radiation is introduced in the next section [1][2][3][4][5][6][7][8][9]. The passive, and the hybrid Q-switching are discussed in . The passive, and the hybrid modelocking are described in Sect. 3. A distinction is made between the mode-locking of low-gain and high-gain active media [35 45]. The simultaneous Qswitching and mode-locking is discussed shortly in Sect. 4. A final section is devoted to the intra-cavity and extra-cavity pulse shortening with saturable absorbers [46][47][48][49][50].

Compression of picosecond light pulses of a hybridly mode-locked pulsed Nd : glass laser

“…In the experiments a Nd:phosphate glass laser oscillator (Schott laser glass type LG703) is actively modelocked by an acousto-optic modulator [43,44] (IntraAction Model ML-50Q, 50 MHz acoustic frequency, 325 kHz mode-spacing) and passively modelocked by a saturable absorber [37][38][39]45] (Kodak dye No. 9860, single pass small signal transmission 7 o =0.85).…”

Cavity length dependence of mode beating in passively Q-switched Nd-solid state lasers.

“…However, there is a limit to the allowed mode locking frequency or repetition rate in a QSML pulse train. The gain or lasing bandwidth limits the maximum mode locking frequency by controlling the number of longitudinal modes that can reach threshold and thus beat together in phase, a required condition for mode locking [25].…”

“…This transition must be able to modulate the gain/loss of the resonator on a time scale faster than the cavity round trip time to phase lock longitudinal modes [25]. Using the published excited state lifetime values in the literature of ~ 550 to 100 ps, the mode locking frequency (repetition rate) is estimated to be from 1.8 GHz to 10 GHz.…”

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

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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.

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“…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].…”