High-average-power and high-conversion-efficiency continuous wave mode-locked Nd:YVO4 laser with a semiconductor absorber mirror
Introduction
Since the first cw mode-locked (CML) solid-state laser with SESAM was demonstrated the mode-locked solid-state lasers were well developed in recent years [1], [2], [3], [4], [5]. One of the important frontiers is high average power [6]. Picosecond high-power diode-pumped solid-state lasers with good beam quality are attracting growing interest because of numerous applications in medicine, material processing and nonlinear frequency conversion. The main challenges for high-power lasers were Q-switching instabilities and the SESAM damage. With single LD pumping, one group has achieved 6.2 W average output power with a slope efficiency of 35% and the other group has achieved 5.3 W average output power with a conversion efficiency of 30% [7], [8]. The thermal lens of the laser crystal and the SESAM damage were the main reason for the limiting average output power. In this experiment, we used a super SAM as the saturable absorber which had a high damage threshold and we designed the laser cavity elaborately for mitigating the effect of the thermal lens. Finally, we achieved a high average output power of 8.1 W at the maximum incident pump power in CML operation; the optic-to-optic conversion efficiency was about 41%. The nonsaturable losses of the SAM was small and the SAM was not damaged in the experiment.
Section snippets
Theoretical discussion about the thermal lens
It is worthwhile to analyze the thermal lens in the Nd:YVO4 crystal, which affects the output power of the laser and the stability of the resonator. For a laser pumped by a fiber-coupled diode the focal length of the thermal lens fth can be approximately given by [9], [10], [11] Where Kc is the thermal conductivity, ωp is the average pump size in the laser crystal, Pph is the fraction of pump power that results in heating, dn/dT is the thermo-optic coefficient, α
Experimental setup and results
The SAM was grown on GaAs substrate by metal-organic chemical-vapor deposition. The SAM consisted of 22 pairs of GaAs/AlAs quarter-wave Bragg layers with high reflectivity of 99.5% at lasing wavelength of 1064 nm and a 15-nm relaxed In0.3Ga0.7As single quantum well (embedded in the topmost layer of the Bragg stack) for achieving saturable absorption at 1064 nm. The Bragg layers and the In0.3Ga0.7As absorber were grown at temperatures of 720 and 500 °C, respectively. For getting a high damage
Conclusion
We have demonstrated a high-power diode-end-pumped cw mode-locked Nd:YVO4 laser by using a semiconductor absorber mirror as the saturable absorber. Considering the thermal lens effect, we elaborately designed the laser cavity, and obtained 8.1 W of average output power in 8.6 ps Gaussion pulses at a repetition rate of 130 MHz. The maximum optic-to-optic conversion efficiency was about 41%. The Q-switching instability was well suppressed and the cw mode-locked pulse train was stable. The low
References (12)
- et al.
Solid-state low-loss intracavity saturable absorber for Nd:YLF lasers: an antiresonant semiconductor Fabry-Perot saturable absorber
Opt Lett
(1992) - et al.
Diode-pumped passively mode-locked lasers with high average power
Appl Phys B
(2000) - et al.
Passive mode locking of a diode-end-pumped Nd:GdVO4 laser with a semiconductor saturable absorber
Opt Lett
(2003) - et al.
4 ps passively mode-locked Nd:Gd0.5Y0.5VO4 laser with a semiconductor saturable absorber mirror
Opt Lett
(2004) - et al.
1 ps passively mode-locked laser operation of Na,Yb:CaF2 crystal
Opt Express
(2005) Recent developments in compact ultrafast lasers
Nature
(2003)
Cited by (22)
Optimization of the mode-locked Nd:YVO<inf>4</inf> laser with a semiconductor saturable absorber mirror
2013, OptikCitation Excerpt :Because high peak power and high-energy ultrashort laser pulse proves its great potentiality in many scientific and industrial fields, obtaining higher peak power and shorter pulse length and improving stability have become research hotspots. A large number of experiments have been performed on passively mode-locked solid-state lasers [10–15], and some theoretical analysis on this process has been discussed [16,17]. Our work is focused on how to develop an analytic model based on the saturable absorber mode-locking theory developed by Haus [18], considering the effects of group-delay dispersion and self-phase modulation.
Simulation of the passively mode-locked laser with a SESAM
2012, OptikCitation Excerpt :The SESAM generally comprise one or more semiconductor saturable absorber layers monolithically integrated into a mirror structure, which can be employed as an additional intracavity laser element for initialization and stabilization of the mode-locking process [8,9]. In recent years, SESAMs have become a key component in the development of ultrashort pulse solid-state lasers [10–13], and much more experimental results are reported, for instance, 5.3 W, 6.2 W and 8.1 W averaged output power with the conversion efficiency of 31.2%, 35% and 41% were obtained by adopting the SESAMs in Z cavity of Nd:YVO4 mode-locked lasers [14,15], respectively. However, there are many ambiguously answered or even unanswered questions about the dynamic mechanisms involved, such as the evolution process of mode-locking pulse in the whole laser cavity, the overlapping effects of different parameters, and the profile of output soliton pulse.
Optimization of diode-pumped passively Q-switched mode-locked c-cut Nd:GdVO<inf>4</inf> laser with a GaAs saturable absorber
2012, Optics and Laser TechnologyCitation Excerpt :Laser-diode-pumped passively Q-switched mode-locked (QML) lasers are ideal for many applications such as micromachining, ranging, remote sensing, etc. GaAs, due to the virtues of large optical nonlinearity, a high damage threshold and a high linear transmission, is one of the most commonly used saturable absorbers to generate QML laser pulses and has been successfully demonstrated in different laser media [1–8]. Although the mode locking mechanism of GaAs single crystal is not very clear, it is believed that the two-photon absorption (TPA) and free-carrier absorption (FCA) effects play an important role in the pulse formation [9].
Ultrafast laser performance of Yb <sup>3 +</sup>: Sc <inf>2</inf>SiO <inf>5</inf> crystal with a single-walled carbon nanotube absorber
2012, Optics CommunicationsCitation Excerpt :Over the past few decades, semiconductor saturable absorber mirrors (SESAMs) play an important role in generating ultrafast pulses [1–3]. However, SESAMs have some disadvantages, such as low damage threshold [4], limited pulse duration and narrow operation wavelength range. In addition, SESAMs demand challenging and expensive fabrication processes [5].
Picosecond laser oscillator with a cavity design for stable CW mode-locking operation
2010, Optics and Laser Technology