Bulk Solid-state Lasers Research Articles

Nanosecond and femtosecond lasers based on black arsenic-phosphorus alloys saturable absorber

In this paper, the high-repetition-rate passively Q-switched (PQS) and the femtosecond continuous-wave mode-locked (CWML) lasers are successfully obtained with 2D black arsenic-phosphorus (b-AsP) nanosheets as saturable absorber (SA) at 1 μm for the first time, to the best of our knowledge. The saturable absorption properties and ultrafast carrier dynamics of the 2D b-AsP SA are explored by Z-scan and pump-probe techniques. Moreover, according to the measurement of desired nonlinear optical characteristics of the relaxation time of 27 ps and the modulation depth of 7.14%, the PQS and CWML lasers are demonstrated with the highest repetition rate of 2.26 MHz in the PQS laser and the pulse width of 470 fs in the CWML laser. The results show 2D b-AsP SA has enormous potential for pulse modulation in solid-state bulk lasers.

RE-Based Inorganic-Crystal Nanofibers Produced by Electrospinning for Photonic Applications.

Electrospinning is an effective and inexpensive technique to grow polymer materials in nanofiber shape with exceptionally high surface-area-to-volume ratio. Although it has been known for about a century, it has gained much interest in the new millennium thanks to its low cost and versatility, which has permitted to obtain a large variety of multifunctional compositions with a rich collection of new possible applications. Rare-earth doped materials possess many remarkable features that have been exploited, for example, for diode pumped bulk solid-state lasers in the visible and near infrared regions, or for biomedical applications when grown in nanometric form. In the last few decades, electrospinning preparation of rare-earth-doped crystal nanofibers has been developed and many different materials have been successfully grown. Crystal host, crystal quality and nanosized shape can deeply influence the optical properties of embedded rare earth ions; therefore, a large number of papers has recently been devoted to the growth and characterization of rare earth doped nanofibers with the electrospinning technique and an up-to-date review of this rapidly developing topic is missing; This review paper is devoted to the presentation of the main results obtained in this field up to now with particular insight into the optical characterization of the various materials grown with this technique.

Few-layer GaSe nanosheet-based broadband saturable absorber for passively Q-switched solid-state bulk lasers.

In this paper, few-layer two-dimensional (2D) GaSe nanosheets were fabricated and utilized as broadband saturable absorbers (SAs) for passively Q-switched (PQS) solid-state bulk lasers operating at 1.06 and 1.99 µm. For 1.06 µm laser operation, the maximum average output power, the shortest pulse width, and the largest single pulse energy were determined to be 438 mW, 285 ns, and 2.31 µJ, respectively, while for 1.99 µm PQS laser operation, they were 937 mW, 383 ns, and 9.56 µJ. Our results identified the great potential applications of few-layer 2D GaSe nanosheets for practical optical modulators such as SAs for pulsed laser generation.

Luminescent ion-doped transparent glass ceramics for mid-infrared light sources [invited

Glass ceramics (GCs), which consist essentially of a homogeneous solid state dispersion of nanocrystals (NCs) embedded in a chemically inert and mechanically robust glass matrix, appear to be an extremely promising class of solid state materials that can be easily tailored into arbitrary shapes, including a new generation of optical fibers, for efficient incoherent and coherent sources of mid-infrared (MIR) light emission. This unique capability not only stems from the fact that one can tailor the underlying glass matrix for optimal macroscopic physical properties and ultrahigh transparency at the wavelengths of interest (resulting in appropriate "transparent glass ceramics" or TGCs), but also stems from the fact that one can embed these matrices with size and structure-tailored NCs, which in turn can be doped with relatively high concentrations of MIR emitting rare-earth or transition metal ions. This potential is tantamount to the localization of these highly efficient MIR ionic emitters into carefully selected and highly favorable "process-engineered" custom crystalline host "nanocages," while insulating the ionic emitters from the emission-quenching glass host matrix, the latter being chosen largely because of its highly favorable macroscopic bulk properties, including its ductility and formability into near-arbitrary shapes (at appropriate temperatures). Such MIR TGCs appear to be very promising for numerous photonics applications, including compact and relatively efficient waveguide sensors, broadband incoherent MIR light sources, superluminescent light sources, advanced fiber-optic devices, and broadly wavelength-tunable and ultrashort pulse mode-locked fiber and bulk solid-state lasers. In this paper, we review past achievements in this field, starting with an overview of TGCs, followed by discussions of currently preferred methods of fabrication, characterization, and optimization of suitably doped oxyfluoride, tellurite, and chalcogenide TGCs and of our projections of anticipated future developments in this field at both the materials and device levels.

Low-dimensional saturable absorbers for ultrafast photonics in solid-state bulk lasers: status and prospects

Abstract Low-dimensional (LD) materials have originated a range of innovative applications in photonics and optoelectronics owning to their advantages of ultrafast carrier response and distinct nonlinear saturable absorption properties. In particular, these emerging LD materials including zero-, one-, and two-dimensional materials have recently been utilized for short and ultrashort pulse laser generation in the visible, near infrared, and mid-infrared wavelength regions. Here, we review recent progress demonstrating the application of LD materials as versatile, wideband saturable absorbers for Q-switching and mode-locking in all-solid-state lasers. The laser performance in operating wavelength, output power, pulse width, repetition rate, and pulse energy is reviewed. Finally, the challenges and future perspectives are suggested.

MXene saturable absorber for nanosecond pulse generation in a mid-infrared Ho,Pr:LLF bulk laser

In this paper, high quality few-layer MXene-Ti3C2Tx was fabricated by the LPE method and successfully applied as saturable absorber for a passively Q-switched (PQS) Ho,Pr:LLF laser operating at 2.95 µm. The maximum average output power was determined to be 105 mW with a slope efficiency of 5%. The shortest pulse width and the largest pulse repetition rate were determined to be 266.7 ns and 83.24 kHz, corresponding to the single pulse energy and pulse peak power of 1.26 µJ and 4.73 W, respectively. It is the first demonstration of MXenes applied in mid-infrared (MIR) PQS solid-state bulk lasers, to the best of our knowledge. The results not only verify the broadband nonlinear saturable absorption properties of MXenes, but also pave the way for exploring their applications in photonic devices.

Passively Q-switched 1.989 μm all-solid-state laser based on a WTe2 saturable absorber.

In this paper, the novel two-dimensional (2D) tungsten ditelluride (WTe2) was successfully fabricated by the liquid phase exfoliation method and used as a saturable absorber (SA) for a diode-end-pumped passive Q-switching Tm:YAP laser operating at the 2.0μm wavelength band. The saturable fluence and the modulation depth of the prepared WTe2 SA were determined to be 5.1 μJ/cm2 and 7.2%, respectively. The maximum average output power of 0.64W was obtained with the shortest pulse width of 368ns at a pulse repetition rate of 78kHz. The corresponding highest single pulse energy and largest pulse peak power were calculated to be 4.8μJ and 12.7W, respectively. To the best of our knowledge, this is the first time that WTe2 has been used as the SA for 2.0μm solid-state bulk lasers. The results indicate that WTe2 should be an excellent SA for generating 2.0μm pulsed lasers.

Recent Progress in Broadband Carbon Nanotube Saturable Absorbers for Ultrafast Bulk Solid-State Lasers

Carbon nanotubes (CNTs) are one of the most investigated nanomaterials for a variety of applications due to their unique electronic and optical characteristics. Over the last two decades, CNTs have been widely investigated to develop efficient passive mode-locking devices applicable for diverse ultrafast laser systems, because they exhibit high nonlinearity, photo-excited ultrafast carrier recovery, broadband applicability and relatively easy processes for device fabrication. In this overview article, recent progress of CNT-based saturable absorbers applicable for mode-locking ultrafast bulk solid-state lasers operating in a broad spectral range between 800 nm and 2100 nm will be reviewed.

Sub-100 fs Tm:MgWO4 laser at 2017 nm mode locked by a graphene saturable absorber.

We present the first sub-100fs bulk solid-state laser in the 2-μm spectral range employing the monoclinic Tm3+-dopedMgWO4 crystal as an active medium. By applying a graphene-based saturable absorber and chirped mirrors for dispersion management, stable self-starting mode-locked operation at 2017nm was achieved. Nearly Fourier-limited pulses as short as 86fs featuring a bandwidth of 53nm were generated at a repetition rate of 76MHz. A pulse energy of 1.1nJ was achieved at 87MHz for a pulse duration of 96fs. The mode-locked Tm3+:MgWO4 laser exhibits excellent stability with a fundamental beat note extinction ratio of 80dBc above noise level.

Diode pumped cascade Er:Y2O3 laser

A cascade, diode-pumped, continuous wave (CW), dual-wavelength operation in a 0.5% Er3+:Y2O3 cryogenic ceramic laser is demonstrated for the first time. The laser operates on cascaded Er (4I11/2 → 4I13/2 → 4I15/2) transitions and can deliver 24 and 13 W at 1.6 and 2.7 μm, respectively. The overall efficiency with respect to the absorbed ~980 nm power was 62%. This is, to our best knowledge, the first demonstration of an efficient, high power, cascade, erbium laser achieved in bulk solid-state lasers. The analysis of the output power, the laser’s wavelengths and slope efficiency for each individual laser transition are presented for pure CW operation mode. Also presented are the temporal behaviors of each laser line as a function of pump pulse duration in the quasi-CW regime.

Ultrasensitive nonlinear absorption response of large-size topological insulator and application in low-threshold bulk pulsed lasers.

Dirac-like topological insulators have attracted strong interest in optoelectronic application because of their unusual and startling properties. Here we report for the first time that the pure topological insulator Bi2Te3 exhibited a naturally ultrasensitive nonlinear absorption response to photoexcitation. The Bi2Te3 sheets with lateral size up to a few micrometers showed extremely low saturation absorption intensities of only 1.1 W/cm2 at 1.0 and 1.3 μm, respectively. Benefiting from this sensitive response, a Q-switching pulsed laser was achieved in a 1.0 μm Nd:YVO4 laser where the threshold absorbed pump power was only 31 mW. This is the lowest threshold in Q-switched solid-state bulk lasers to the best of our knowledge. A pulse duration of 97 ns was observed with an average power of 26.1 mW. A Q-switched laser at 1.3 μm was also realized with a pulse duration as short as 93 ns. Moreover, the mode locking operation was demonstrated. These results strongly exhibit that Bi2Te3 is a promising optical device for constructing broadband, miniature and integrated high-energy pulsed laser systems with low power consumption. Our work clearly points out a significantly potential avenue for the development of two-dimensional-material-based broadband ultrasensitive photodetector and other optoelectronic devices.

Highly efficient passively Q-switched solid-state 2 μm laser with monolayer Graphene

By using monolayer graphene as saturable absorber, a passively Q-switched Tm:LuAG laser with high efficiency at 2 μm is demonstrated. At the incident pump power of 5.8 W, pulses with duration of 235 ns and maximum average output power of 873 mW were obtained at a repetition rate of 72 kHz. This is, to the best of our knowledge, the highest average output power, as well as the narrowest pulse width, ever obtained among graphene-based passively Q-switched solid-state bulk lasers at 2 μm regime.

Wavelength-versatile graphene-gold film saturable absorber mirror for ultra-broadband mode-locking of bulk lasers.

An ultra-broadband graphene-gold film saturable absorber mirror (GG-SAM) with a spectral coverage exceeding 1300 nm is experimentally demonstrated for mode-locking of bulk solid-state lasers. Owing to the p-type doping effect caused by graphene-gold film interaction, the graphene on gold-film substrate shows a remarkably lower light absorption relative to pristine graphene, which is very helpful to achieve continuous-wave mode-locking in low-gain bulk lasers. Using the GG-SAM sample, stable mode-locking is realized in a Yb:YCOB bulk laser near 1 μm, a Tm:CLNGG bulk laser near 2 μm and a Cr:ZnSe bulk laser near 2.4 μm. The saturable absorption is characterised at an intermediate wavelength of 1.56 μm by pump-probe measurements. The as-fabricated GG-SAM with ultra-broad bandwidth, ultrafast recovery time, low absorption, and low cost has great potential as a universal saturable absorber mirror for mode-locking of various bulk lasers with unprecedented spectral coverage.

Beam Shaping Technology for High Power Diode Laser Source

Direct diode lasers have some of the most attractive features of any laser. They are very efficient, compact, wavelength versatile, low cost, and highly reliable. However, the full utilization of direct diode lasers has yet to be realized. This is mainly due their poor output beam quality. Because of this, direct diode lasers are typically used to pump other lasers such as bulk solid-state (rod and thin disk) and fiber lasers. An improvement of the wall-plug efficiency and Power density necessary can be achieved by beam shaping and beam combination such as polarization coupling. In this paper, using the beam shaping technology realize good beam quality and high wall-plug efficiency. Base on bars rated to 60 W and 57% conversion efficiency, vertically stacked arrays (twenty bars) of such configuration are demonstrated with rated to about 1200W. The beam quality of high-power high brightness 880 nm laser diode source is improved with beam shaping. Beam parameter product of 79. 3 mm mrad ×81. 2 mm mrad, electro-optical conversion efficiency of more than 45.8% and continuous output power of 1 kW are demonstrated. This laser can be directly applied to cladding, surface hardening and other fields.

Experimental Investigation on Evolution of the Beam Quality in a 2-kW High Power Fiber Amplifier

The M2 value is a general metric to characterize the beam quality of the high power fiber lasers. In this letter, we demonstrated a near single-mode fiber amplifier with 2.04 kW output. To the best of the authors' knowledge, we present the first evolution of the beam quality as a function of the signal output power in a multikilowatt class fiber laser utilizing step-index large-mode-area fiber. The M2 parameter of was preserved at any power level without mode instability. What is more, the evolution of the beam quality and the mode field experimentally verifies the superior thermal-optical property of the high power fiber lasers compared with other bulk solid-state lasers because of their geometry of the gain medium.

Optical refrigeration to 119 K, below National Institute of Standards and Technology cryogenic temperature

We report on bulk optical refrigeration of Yb:YLF crystal to a temperature of ~124 K, starting from the ambient. This is achieved by pumping the E4-E5 Stark multiplet transition at ~1020 nm. A lower temperature of 119±1 K (~-154C) with available cooling power of 18 mW is attained when the temperature of the surrounding crystal is reduced to 210 K. This result is within only a few degrees of the minimum achievable temperature of our crystal and signifies the bulk solid-state laser cooling below the National Institute of Standards and Technology (NIST)-defined cryogenic temperature of 123 K.

12-GHz repetition rate, diode-pumped femtosecond Yb:KYW laser mode-locked by a carbon nanotube saturable absorber mirror

We demonstrate a 1.2-GHz repetition rate, diode-pumped, self-starting, 168-fs (FWHM) pulsewidth Yb:KYW laser mode-locked by a carbon nanotube (CNT) saturable absorber mirror. To our knowledge, this result corresponds to the highest repetition rate from CNT-mode-locked femtosecond bulk solid-state lasers, reaching the GHz regime for the first time.

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.

High-quality, large-area monolayer graphene for efficient bulk laser mode-locking near 1.25 μm.

High-quality monolayer graphene as large as 1.2×1.2 cm2 was synthesized by chemical vapor deposition and used as a transmitting saturable absorber for efficient passive mode-locking of a femtosecond bulk solid-state laser. The monolayer graphene mode-locked Cr:forsterite laser was tunable around 1.25 μm and delivered sub-100 fs pulses with output powers up to 230 mW. The nonlinear optical characteristics of the monolayer graphene saturable absorber and the mode-locked operation were then compared with the case of the bilayer graphene saturable absorber.

Fiber Optics for Multilayered Optical Memory

We have developed a compact and high-power mode-locked fiber laser for multilayered optical memory. Fiber lasers have the potential to be compact and stable light sources that can replace bulk solid-state lasers. To generate high-power pulses, we used stretched-pulse mode locking. The average power and pulse width of the output pulse from the fiber laser that we developed were 109 mW and 2.1 ps, respectively. The dispersion of the output pulse was compensated with an external single-mode fiber of 2.5 m length. The pulse was compressed from 2.1 ps to 93 fs by dispersion compensation. The fiber laser we have developed is possible to use as a light source of multilayered optical memory. We also present a fiber confocal microscope as an alignment-free readout system of multilayered optical memories. The fiber confocal microscope does not require fine pinhole position alignment because the fiber core is used as the point light source and the pinhole, and both of which are always located at the conjugated point. The configuration reduces the required accuracy of pinhole position alignment. With these techniques we can present an all-fiber recording and readout system for multilayered memories.