Mode-locked Solid-state Lasers Research Articles

Dynamics of solid-state lasers pumped by mode-locked lasers.

We analyze the dynamics of mode-locked pumped solid-state lasers focusing on the transition between mode-locked and CW behavior. Where the ratio of the pump and laser cavity lengths is a rational number, 'rational-harmonic mode-locking' is obtained. When the cavity length is detuned away from such resonances, modulated continuous output is generated. The transition from mode-locked to modulated CW operation is explored experimentally for a Ce:LiCAF laser operating at 290 nm and pumped by a 78.75 MHz mode-locked frequency quadrupled Nd:YVO(4) laser. Both CW output and mode-locked output with pulse repetition rates up to 1.1 GHz were achieved. A rate equation model is developed to predict optimum cavity lengths for achieving CW output with minimized modulation.

Fundamental Limits to Mode-Locked Lasers: Toward Terawatt Peak Powers

Most mode-locked solid-state lasers are based on soliton solutions of the cubic Ginzburg-Landau equation. Their performance is close to theoretical limits, and new design paradigms will be needed if solid-state systems are to continue to improve at their historically aggressive rates. Through comprehensive analysis of the interplay of group-velocity dispersion, nonlinear refraction, spectral filtering, and saturable absorption, we identify the factors that fundamentally limit the achievable peak power of solid-state lasers. Numerical calculations that accurately model existing solid-state lasers are used to assess new designs. In particular, we focus on normal-dispersion cavities, which support dissipative solitons. The calculations reveal that the gain bandwidth, modulation depth of the saturable absorber, and nonlinear phase accumulation present the primary limitations to the peak power. We assess these limitations in Ti:sapphire, Yb:KGW, and thin-disk oscillators. Guidelines for the optimum designs are presented, and we show that dissipative soliton pulse-shaping in cavities with net normal dispersion can fundamentally allow performance improvements of several orders of magnitude. High-performance oscillators should offer low-noise, low-cost alternatives to some current amplifier-based systems.

SESAM mode-locked red praseodymium laser.

We present the first semiconductor saturable absorber mirror (SESAM) mode-locked praseodymium solid-state laser. The laser is based on a Pr(3+):LiYF(4) crystal as gain medium and a GaInP-quantum well-based SESAM. Self-starting continuous-wave mode-locked laser operation with an average output power of 16 mW is achieved at a center wavelength of 639.5 nm. The laser operates at a repetition rate of ∼85.55 MHz and emits pulses with a duration of ∼18 ps.

Graphene mode-locked Cr:ZnS chirped-pulse oscillator

We report the first to our knowledge high-energy graphene mode-locked solid-state laser operating in the positive dispersion regime. Pulses with 15.5 nJ energy and 42 nm spectral bandwidth with 0.87 ps duration were obtained at 2.4 μm wavelength. The output can be compressed down to 189 fs. The graphene absorber damage threshold was established at fluence approaching 1 mJ/cm².

Transient behaviour of quantum-dot saturable absorber mirrors at varying excitation fluence

We present results from studying the carrier dynamics in self-assembled InAs/GaAs quantum-dot saturable absorbers intended for mode-locking of solid-state lasers. Four samples are examined, featuring controlled variations in the resonance condition of the electric field inside the absorber, the number of quantum-dot (QD) layers and the thickness of the GaAs barriers between these QD layers. Pump-probe experiments are conducted at a wide range of excitation fluences and reveal a fast relaxation component of the initial bleaching at low excitation fluences, while a slowly relaxing induced transparency becomes dominant at higher excitation fluences. Time-resolved photoluminescence measurements reveal a large and slowly relaxing induced transparency due to a capture of excess carriers from the barrier bands into the QDs and a slow radiative recombination there. The resonance condition as well as the thickness of the barriers between the QD layers can be used to control the relaxation behaviour. The fastest response is obtained in a structure with an increased number of QD layers at each individual anti-node of the electric field, which is attributed to the appearance of efficient non-radiative recombination channels and capture centres. These centres are probably related to dislocations and other defects appearing in thick QD stacks.

蓬勃发展的高重复频率固体锁模激光器

蓬勃发展的高重复频率固体锁模激光器

A Review of Cavity Design for Kerr Lens Mode-Locked Solid-State Lasers

We provide a critical review of the fundamental concepts of Kerr lens mode-locking (KLM), along with a detailed description of the experimental considerations involved in the realization of a mode-locked oscillator. In addition, we review recent developments that overcome inherent limitations and disadvantages in standard KLM lasers. Our review is aimed mainly at readers who wish to realize/maintain such an oscillator or for those who wish to better understand this major experimental tool.

Watt-level passively Q-switched mode-locked YVO4/Nd:YVO4 laser operating at 1.06µm using graphene as a saturable absorber

Abstract High-quality monolayer graphene films with large area were grown on Cu foils by the chemical vapor deposition (CVD) technique. For the first time, graphene saturable absorbers (SAs) with well-defined layer numbers were fabricated by controlling of transfer process precisely. Using the graphene SAs, stable Q-switched mode-locking pulse trains with a nearly 100% modulation depth were realized in a diode-pumped YVO4/Nd:YVO4 laser. At the pump power of 6.0 W, the average output power reached a high value of 1.6 W. To the best of our knowledge, this is the highest output power of passively mode-locked solid-state laser using graphene SA, suggesting that the low-cost, broadband graphene SA could potentially be employed in practical high-power mode-locking laser system.

Sub-100 attosecond timing jitter from low-noise passively mode-locked solid-state laser at telecom wavelength

We report on the ultralow timing jitter of the 100 MHz pulse trains generated by two identical passively mode-locked diode-pumped solid-state lasers (DPSSLs) emitting at 1556 nm. Ultralow timing jitter of 83 as (integrated from 10 kHz to 50 MHz) for one laser has been measured with a balanced optical cross-correlator as timing discriminator. Extremely low intensity noise has been measured as well. Several measurement techniques have been used and show similar jitter results. Different possible noise sources have been theoretically investigated and compared to the measured jitter power spectral density. It is found that although the measured integrated jitter is quite low, it is still significantly above the quantum limit in the considered frequency span. Therefore, there is a substantial potential for technical improvements that could make passively mode-locked DPSSL outperform fiber lasers as source of microwaves with low phase noise.

Mode-locking of solid-state lasers by single-walled carbon-nanotube based saturable absorbers**Reported at the XIX International Conference on Advanced Laser Technologies, Bulgaria, Golden Sands, September 2011.

Universal use of single-walled carbon-nanotube based saturable absorber devices for mode-locking of bulk solid-state lasers between 0.8 and 2 μm is discussed. The advantages in comparison to semiconductor saturable absorbers are emphasised. We briefly describe the manufacturing process and the essential optical properties, and review experimental results obtained with various typesof femtosecond and picosecond solid-state lasers in the steady-state regime. We also demonstrate that a single hybrid saturable absorber used in transmission can be used to mode-lock four different types of lasers operating between 1 and 2 μm.

Dual-polarization mode-locked Nd:YAG laser

A mode-locked solid-state laser containing a birefringent element is shown to emit synchronously two frequency combs associated to the two polarization eigenstates of the cavity. An analytical model predicts the polarization evolution of the pulse train, which is determined by the adjustable intracavity birefringence. Experiments realized with a Nd:YAG laser passively mode locked by a semiconductor saturable absorber mirror are in perfect agreement with the model. Locking between the two combs arises for particular values of their frequency difference, e.g., half the repetition rate, and the pulse train polarization sequence is then governed by the relative overall phase offset of the two combs.

Broadband single-walled carbon nanotubes absorber for solid-state ultrafast lasers

The single-walled carbon nanotubes (SWCNT) absorber was fabricated by vertical evaporation method. Mode-locked picosecond Nd-doped solid-state lasers operating at 1.00 and 1.34 μm and Tm-doped solid-state laser at 2 μm with SWCNT absorbers were demonstrated, respectively. Watt-level average output powers of continuous wave mode locking were obtained. The operational bandwidth of 1 μm is broader than other saturable absorbers fabricated by using other types of materials.

High power passively mode-locked Nd:YVO4 laser using graphene oxide as a saturable absorber

We report on a passively mode-locked Nd:YVO4 laser using a novel graphene oxide saturable absorber fabricated by vertical evaporation method. An 880 nm LD pump source was used to reduce the thermal load of the laser crystal. At the pump power of 7.4 W, 1.2 W average output power of continuous wave mode-locked laser with optical conversion efficiency of 16.2% was achieved. To the best of our knowledge, this is the highest output power of passively mode-locked solid-state laser using graphene oxide saturable absorber. The repetition rate of passively mode-locked pulse was 88 MHz with the pulse energy of 13.6 nJ.

Periodic adjustment of the position of a laser beam spot on a semiconductor saturable absorber mirror in a passively mode-locked solid-state laser

A laser diode end-pumped passively mode-locked Nd:YVO4 solid-state laser with a semiconductor saturable absorber mirror (SESAM), in which the intracavity laser beam spot on the SESAM can be adjusted periodically, is investigated. Inserting a rectangular prism (RP) into the laser cavity is a promising approach towards the goal of periodically moving the position of the focus spot of the intracavity pulse on the SESAM surface to avoid the long-time irradiation of the laser beam on the same position, thereby solving a series of problems caused by damage to the SESAM and greatly prolonging its usage life. The adjustment of the rectangular prism in the laser cavity does not break the stable continuous wave (CW) mode-locked condition. The laser generates a stable picosecond pulse sequence at 1064 nm with an output power of 3.6 W and a pulse width of 14 ps. The instabilities of the output power and the pulse width are 1.77% and 4.5%, respectively.

Solid-State Laser Mode-Locking Near 1.25 μm Employing a Carbon Nanotube Saturable Absorber Mirror

We demonstrate passive mode-locking of a Cr:forsterite laser with a single-walled carbon nanotube saturable absorber mirror (SWCNT-SAM). Without compensation of intra-cavity dispersion, the self-mode-locked laser generates 11.7 ps pulses at a repetition rate of 86 MHz. The dispersion-compensated laser yields ultrashort pulses as short as 80 fs near <TEX>$1.25\;{\mu}m$</TEX> at 78 MHz with average output powers up to 295 mW, representing the highest power ever reported for mode-locked solid-state lasers based on saturable absorption of SWCNTs in this spectral region.

基于石墨烯可饱和吸收被动锁模超快全固体激光器的研究

基于石墨烯可饱和吸收被动锁模超快全固体激光器的研究

Investigation on mode matching including thermal effects in LD end-pumped passively mode-locked Nd:YVO4 laser

We design a laser diode (LD) end-pumped passively mode-locked solid-state laser with a semiconductor saturable absorber mirror. Mode-matching efficiency in the active medium including the thermal effect is analyzed, and the optimum mode-matching coefficient is obtained by optimizing the pump mode. In the experiment, a total power of 4.2 W stable pulse sequences without multipulse at 1064 nm is obtained with a pulse repetition rate of 86 MHz and a pulse width of 13 ps, corresponding to a high optical to optical efficiency of 44%.

Instabilities in intracavity pumped optical parametric oscillators and methods of stabilization

A high conversion efficiency and stability are the anticipated advantages of intracavity pumped parametric oscillators, as opposed to the traditional externally pumped ones. The dynamics of the coupled pump and signal cavities, however, is very complex and poses a considerable design challenge. In this paper we present a simulation of an optical parametric oscillator, pumped intracavity by a mode-locked solid-state laser. Different unstable modes of operation are identified in an experimental setup and the simulation is used to reproduce and analyze them. Based on this analysis we present techniques to amplitude stabilize the system.

Single-passed passively mode-locked Nd:YVO4 picosecond laser with SESAM

We report on the LD-pumped passively mode-locked solid-state laser with SESAM (semiconductor saturable absorber mirror), in which the output beam is single passed through a flat mirror. The CW mode-locking pulse at 1064 nm, with an output power of 5 W, a pulse repetition rate of 98 MHz, and a pulse width of 25.3 ps. The beam quality is M2 < 1.12 and the optical-optical efficiency is 35.7%.

High frequency measurements on an AlN∕GaN-based intersubband detector at 1550 and 780nm

We report on high frequency measurements on an AlN∕GaN-based intersubband detector using mode-locked solid state lasers. Our experiments involving laser wavelengths of 1550 and 780nm demonstrate not only the capability of such devices to work both at the fundamental and at a higher order intersubband transition, but they also allowed us to push the high frequency detection limit up to a value of 13.3GHz. From the shape of the harmonic decay, we conclude that this limit is not due to intrinsic properties of the detector.