Search

Interlayer vibrations with discrete quantized modes in two-dimensional (2D) materials can be excited by ultrafast light due to the inherent low dimensionality and van der Waals force as a restoring force. Controlling such interlayer vibrations in layered materials, which are closely related to fundamental nanomechanical interactions and thermal transport, in spatial- and time-domain provides an in-depth understanding of condensed matters and potential applications for advanced phononic and photonics devices. The manipulation of interlayer vibrational modes has been implemented in a spatial domain through material design to develop novel optoelectronic and phononic devices with various 2D materials, but such control in a time domain is still lacking. We present an all-optical method for controlling the interlayer vibrations in a highly precise manner with Bi2Se3 as a promising optoelectronic and thermoelasticity material in layered structures using a coherently controlled pump and probe scheme. The observed thickness-dependent fast interlayer breathing modes and substrate-induced slow interfacial modes can be exactly explained by a modified linear chain model including coupling effect with substrate. In addition, the results of coherent control experiments also agree with the simulation results based on the interference of interlayer vibrations. This investigation is universally applicable for diverse 2D materials and provides insight into the interlayer vibration-related dynamics and novel device implementation based on an ultrafast timescale interlayer-spacing modulation scheme.

Interlayer vibrations with discrete quantized modes in two-dimensional (2D) materials can be excited by ultrafast light due to the inherent low dimensionality and van der Waals force as a restoring force. Controlling such interlayer vibrations in layered materials, which are closely related to fundamental nanomechanical interactions and thermal transport, in spatial- and time-domain provides an in-depth understanding of condensed matters and potential applications for advanced phononic and photonics devices. The manipulation of interlayer vibrational modes has been implemented in a spatial domain through material design to develop novel optoelectronic and phononic devices with various 2D materials, but such control in a time domain is still lacking. We present an all-optical method for controlling the interlayer vibrations in a highly precise manner with Bi

Mode-locked lasers emitting ultrashort pulses in the 2-μm spectral range at high (100-MHz) repetition rates offer unique opportunities for time-resolved molecular spectroscopy and are interesting as pump/seed sources for parametric frequency down-conversion and as seeders of ultrafast regenerative laser amplifiers. Passively mode-locked lasers based on Tm3+- and Ho3+-doped bulk solid-state materials have been under development for about a decade. In 2009 we demonstrated the first steady-state operation of such a Tm:KLu(WO4)2 laser using a single-walled carbon nanotube (SWCNT) saturable absorber (SA), generating 10-ps pulses at 1.95 μm. In 2012 this laser produced 141-fs pulses at 2.037 μm. More recently, the study of numerous active media with different SAs resulted in the generation of sub-100-fs (sub-10-optical-cycle) pulses. Materials with broad and smooth spectral gain profile were selected, naturally emitting above 2 μm to avoid water vapor absorption/dispersion effects, including anisotropic materials, strong crystal-field distortion in hosts that do not contain rare-earths, crystals with structural or compositional (i.e. mixed compounds) disorder that exhibit inhomogeneous line broadening, mixed laser ceramics, and Tm,Ho-codoping of ordered and disordered crystals and ceramics. A broad absorption band in semiconducting SWCNTs spans from 1.6 to 2.1-μm whereas the absorption of graphene extends into the mid-IR and scales for multilayers, increasing the modulation depth. Compared to GaSb-based semiconductor SA mirrors (SESAMs), the carbon nanostructures exhibit broader spectral response and can be fabricated by simpler and inexpensive techniques. Chirped mirrors were implemented for groupvelocity dispersion compensation, to generate the shortest pulses, down to 52 fs at 2.015 μm.

Graphene has proved to be an excellent broadband saturable absorber for mode-locked operation of ultrafast lasers. However, for the mid-infrared (mid-IR) range where broadly tunable sources are in great needs, graphene-based broadly tunable ultrafast mid-IR lasers have not been demonstrated so far. Here, we report on passive mode-locking of a mid-IR Cr:ZnS laser by utilizing a transmission-type monolayer graphene saturable absorber and broad spectral tunability between 2120 nm and 2408 nm, which is the broadest tuning bandwidth ever reported for graphene mode-locked mid-IR solid-state lasers. The recovery time of the saturable absorber is measured to be ~2.4 ps by pump-probe technique at a wavelength of 2350 nm. Stably mode-locked Cr:ZnS laser delivers Fourier transform-limited 220-fs pulses with a pulse energy of up to 7.8 nJ.

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 types of 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.

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 1.25 µm 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.

Single-walled carbon-nanotube absorbers are experimentally demonstrated for laser mode-locking. A saturable absorber device is used to mode-lock three different bulk solid-state lasers in a 500 nm-wide wavelength interval. The devices exhibit a low saturation fluence of

Triple-line-shaped electrodes were devised to fabricate a periodically poled 90° domain structure of KNbO 3 (PP90KN) of 20.25 μm period with uniform periodicity and reproducibility. Using the fundamental pulse of 141 fs duration at 1619 nm wavelength, an efficient broadband type-I quasi-phase-matched second-harmonic generation was realized in an 8.3 mm long PP90KN by satisfying both phase matching and group-velocity-matching in the telecommunication L-band at room temperature. Second-harmonic pulses showed no significant temporal and spectral distortion and had a pulse duration of about 144 fs, which agreed well with the theoretical value of 142 fs. The conversion efficiency of the second-harmonic generation was 28.7% at the fundamental pulse energy of 0.92 nJ, which is about 60% of the theoretical value.

We demonstrate a femtosecond Cr:YAG laser mode-locked by a carbon nanotube saturable absorber mirror (CNT-SAM) at a repetition rate of 550 MHz. By employing the CNT-SAM, which exhibits a modulation depth of 0.51% and a saturation fluence of 28 μJ/cm2 at 1.5 μm, we achieved a compact bulk Cr:YAG laser with self-starting mode-locked operation near 1.5 μm, delivering an average output power of up to 147 mW and a pulse duration of 110 fs. To our knowledge, this system provides the highest repetition rate among reported CNT-SAM mode-locked Cr:YAG lasers and the shortest pulse duration among saturable absorber mode-locked Cr:YAG lasers with repetition rates above 500 MHz.

We report on the development of a passively mode-locked near-infrared femtosecond laser with Cr:YAG crystal that operates near room temperature. The laser wavelength could easily be tuned by using only the internal prism pair over 110 nm from 1400 nm to 1510 nm in cw and over about 30 nm in mode-locked operation, respectively Maximum cw output powers of 810 mW were obtained with output coupler for absorbed pump powers of 7.6 W. For compensation of the internal group velocity dispersion, an IR graded prism pair was used. The Cr:YAG laser delivered nearly Fourier-transform limited pulses with a pulse duration as short as 64 fs at 100 MHz repetition rate. In the mode-locked regime, the laser was operating at 1510 nm with a spectral bandwidth of 44 nm. In order to avoid unstable mode-locking and power instabilities, self-built tubes were inserted into the beam path in the resonator and purged with N2 gas. Finally, output powers of the Cr:YAG laser were optimized to 250 mW fer long time stable mode-locked operation.

We demonstrate a passively Q-switched thulium fiber laser, using a graphene-based saturable absorber. The laser is based on an all-fiber ring cavity and produces ∼2.3 μs pulses at 1884nm, with a maximum pulse energy of 70 nJ.

Thulium (Tm) lasers operating in the 2 m IR spectral range are interesting for many applications, including spectroscopy, remote sensing, photomedicine, optical communications, and metrology. For instance, in photomedicine, 2 m lasers may be used in ophthalmology to treat glaucoma (high pressure in the eye) by iridotomy, in which holes are made in the iris. Another ophthalmic 2 m laser application is to cut a hole in the back of the capsule that contains the lens of the eye (capsulotomy). Lasers at this frequency are also used in dermatology to reduce skin wrinkles. An interesting feature of such 2 m lasers is that water (the main component of human tissue) is absorbed very efficiently, more than at 1 m, which is produced by the wellknown Nd:YAG (neodymium:yttrium aluminum garnet) laser. Saturable absorbers (SAs) can be employed to realize both passive mode-locking and passive Q-switching of such lasers. As the intensity increases in the laser cavity, the SAs become more and more transparent until the absorption saturates. This is called absorption bleaching. Energy absorbed by the SAs is released in a laser pulse, and the same process starts again. By using the mode-locked technique, it is possible to obtain ultrashort (femtosecond) pulse durations, depending on the breadth of the gain bandwidth of the material. For ophthalmic applications, the extremely short illumination time of a femtosecond pulse will produce less heating of ocular tissue. Consequently, a mode-locked Tm laser will be particularly suitable for iridotomy. On the other hand, passive Q-switching, which is simpler than active Q-switching, can be used to realize compact, robust, and inexpensive sources of high-energy short pulses in this wavelength range. As a result, the Q-switched Tm laser with Figure 1. Autocorrelation trace (a) and laser spectrum (b) of a modelocked thulium in potassium lutetium double tungstate laser using a single-walled carbon nanotube-saturable absorber. a.u.: Arbitrary units. FWHM: Full width at half-maximum.

Monoclinic crystals of Tm-doped KLu(WO 4 ) 2 were used to demonstrate pulsed laser operation near 2 μm. Passive Qswitching and passive mode-locking were the techniques employed to produce such laser pulses. For passive Qswitching we used an AlGaAs -based diode laser to pump the active elements and Cr:ZnSe and Cr:ZnS crystals as saturable absorbers. For passive mode-locking we used a Ti:sapphire laser as pump source and single-walled carbon nanotubes as saturable absorbers. In the former case, maximum pulse energies of 200 μJ for a pulse duration of 70 ns were achieved at a repetition rate of 3 kHz with Cr:ZnS saturable absorber, while in the latter case, ultrashort pulse durations of ~10 ps were measured with a maximum average power of 240 mW. In both laser regimes the oscillation wavelength was ~1945 nm.

We report on passive mode-locking of a Ti:sapphire laser employing a single-walled carbon nanotube saturable absorber (SWCNT-SA) specially designed and fabricated for wavelengths near 800 nm. Mode-locked pulses as short as 62 fs were generated at a repetition rate of 99.4 MHz. We achieved output powers from the SWCNT-SA mode-locked laser as high as 600 mW with a slope efficiency of 26%. The characteristics of SWCNT-SA-assisted mode-locking were compared with those of Kerr-lens mode-locking without SWCNT-SA.

Octave spanning saturable absorber possessing operation bandwidth of ~1000 nm is fabricated on the basis of single-walled carbon nanotubes and applied for mode-locking of different bulk lasers in the 1 and 2 µm spectral range.

We report on mode locking of a bulk Cr:YAG laser by using a transmission-type single-walled carbon nanotube saturable absorber. Stable and self-starting laser operation in the picosecond and femtosecond regimes is obtained at wavelengths around 1.5 microm. Tunable transform-limited sub-100 fs pulses are generated at a repetition rate of 85 MHz with an output power up to 110 mW.

Monolayer graphene was synthesized and used to develop novel saturable absorbers for bulk solid-state laser mode-locking. The graphene mode-locked Cr:forsterite laser delivers stable 130-fs pulses at 1.25 µ with output powers up to 230 mW.

Transmissive single-walled carbon nanotube saturable absorbers were used for passive mode-locking of a Cr:YAG laser, delivering tunable sub-100-fs pulses around 1.5 µm with output powers up to 110mW at 84.6 MHz.

Controlling bundling and curl of carbon nanotubes permits ultrafast optical switching, which was demonstrated in a >500 nm near-infrated band by femtosecond mode-locking of three bulk lasers using one and the same saturable absorber.

Femtosecond mode-locking of Yb:KYW at 1.04 μm, Cr:forsterite at 1.25 μm and a Cr:YAG at 1.50 μm lasers using one and the same transmission-type single-walled carbon nanotube saturable absorber is demonstrated.

Stable and self-starting mode-locking of a Tm:KLu(WO4)2 laser using a single-walled carbon nanotubes based saturable absorber is demonstrated generating ~10-ps pulses at 1.94 µm with powers up to 220 mW at 126 MHz.

Transmission- and reflection-type single-walled carbon nanotube saturable absorbers (SWCNT-SAs) were designed and fabricated for passive mode-locking of bulk lasers in the 1 microm spectral range. Mode-locked laser operation based on a diffusion-bonded Yb:KYW/KYW crystal was demonstrated, and pulses as short as 83 fs and 140 fs were achieved applying reflection-type and transmission-type SWCNT-SA, respectively. The nonlinear parameters of the absorbers were measured to be in close vicinity to those of a semiconductor saturable absorber mirror for the same wavelength range. Mode-locking performance with SWCNT-SAs and the SESAM was compared utilizing the same cavity, with the SESAM resulting in only slightly shorter pulses of 66 fs duration. The nearly identical performance indicates that well-optimized SWCNT-SAs can substitute SESAMs even in the 1 microm region.

Novel transmission- and reflection-type ultrafast saturable absorbers were developed based on single-walled carbon nanotubes (SWCNTs). Their nonlinear optical characteristics, crucial for mode-locking, such as modulation depth, saturation fluence and recovery time were studied. Additionally, we demonstrated passive mode-locking of different bulk solid-state lasers operating above 1 μm using these SWCNT-SAs and achieved stable femtosecond pulses without q-switching instabilities.

Stable and self-starting mode-locking of a Tm:KLu(WO(4))(2) crystal laser is demonstrated using a transmission-type single-walled carbon nanotube (SWCNT) based saturable absorber (SA). These experiments in the 2 microm regime utilize the E11 transition of the SWCNTs for nonlinear saturable absorption. The recovery time of the SWCNT-SA is measured by pump-probe measurements as approximately 1.2 ps. The mode-locked laser delivers approximately 10 ps pulses near 1.95 microm with a maximum output power of up to 240 mW at 126 MHz repetition rate.

A Cr:forsterite laser passively mode-locked with a transmission-type single-walled carbon nanotube saturable absorber delivers pulses as short as 120 fs near 1.25 μm with a maximum average power of 202 mW at 79.1 MHz.

Mode-locking of the disordered cubic sesquioxide crystal Yb:LuScO 3 using a reflection-type single-walled carbon nanotube saturable absorber is demonstrated under diode pumping and compared with passive mode-locking by a commercial SESAM.

Ultrafast single-walled carbon nanotube saturable absorbers were fabricated and optimized for mode-locking solid-state lasers near 1 mum. Their typical modulation depth and recovery time were measured to be Gt 0.3% and ~ 750 fs, respectively.

Single-walled carbon nanotube saturable absorbers were designed for passive mode-locking near 1 mum. Using Yb:KYW and Yb:KLuW, nearly transform-limited sub-150 fs pulses were generated at 1037 nm and 1048 nm, respectively.

Mode locking of an Yb-doped bulk laser in the 1 microm spectral range using a single-walled carbon nanotube saturable absorber (SWCNT-SA) is demonstrated for the first time, to our knowledge. Passive mode locking of an Yb:KLuW laser resulted in nearly transform-limited pulses as short as 115 fs at 1048 nm. In addition, the nonlinear response of the SWCNT-SA was measured, yielding a modulation depth of 0.25% and a relaxation time of 750 fs.

Single-walled carbon nanotube saturable absorbers were designed and characterized (modulation depth

We demonstrate, for the first time to our knowledge, multikilohertz operation of a double-stage optical parametric chirped pulse amplifier with periodically poled stoichiometric LiTaO3 crystals, seeded by a homemade Cr:forsterite oscillator operating at 1235 nm. The repetition rate of the amplifier could easily be tuned without the use of electro-optic modulators by using a repetition-rate-tunable kilohertz pump laser operating at 532 nm and a time-synchronization unit. Amplified total (signal+idler) energies of 55.9 and 36.2 microJ were achieved at 1 and 5 kHz, respectively. After recompression, the pulse width of amplified idler pulses at 1235 nm amounted to 530 fs.

Double-stage multi-kHz optical parametric chirped pulse amplification is demonstrated near 935 nm and 1235 nm. Using a Cr:forsterite seed laser and two periodically poled stoichiometric LiTaO3 crystals as gain media, total (signal+idler) amplified energies of 55.7 muJ and 35.6 muJ were obtained at 1 kHz and 5 kHz, respectively.

A compact multi-kHz double-stage Cr:forsterite optical parametric chirped pulse amplifier is presented. Using periodically poled stoichiometric LiTaO3, total amplified powers of 92 mW and 290 mW were generated at 1 kHz and 5 kHz, respectively..

We present first experimental results of a non-degenerate single-pass Cr:forsterite optical parametric chirped pulse amplification in periodically poled stoichiometric LiTaO3 at 1 kHz, which delivers muJ-pulses near 935 nm and 1235 nm, respectively.

Bandwidth-limited pulses of sub-50 fs duration at 1506 nm are generated by a Cr:YAG laser mode-locked with a single-walled carbon nanotube saturable absorber. A Stokes shifted sideband at 1626 nm is observed for the broadest oscillation spectra.

We report on mode-locking of a Cr:YAG laser at 1516 nm using a monolayer graphene-based saturable absorber of transmission type generating 91 fs pulses with a Fourier product of 0.38 at an average output power exceeding 100 mW. Stable single-pulse mode-locked operation without any sign of Q-switching instabilities or multiple pulses is achieved.

We demonstrate high-energy soliton-like pulses from a Herriott-type, soft-aperture, Kerr-lens mode-locked Ti:sapphire oscillator. The oscillator operates at a 4.26 MHz repetition rate and generates a pulse energy as high as 330 nJ with a 98 fs pulse duration in a negative dispersion regime. The signal-to-noise ratio at the fundamental frequency shows an extinction ratio of >60 dB relative to the carrier. To the best of our knowledge, this is the highest chirp-free soliton-like pulse energy achieved directly from an oscillator without amplification or cavity dumping. The laser has only a 120 × 60 cm2 footprint based on a single Herriott cell with notches.

We report an erbium-doped, nanotube mode-locked fiber oscillator generating 74 fs pulses with 63 nm spectral width. This all-fiber-based laser is a simple, low-cost source for time-resolved optical spectroscopy, as well as for many applications where high resolution driven by short pulse durations is required.

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.

We report what we believe to be the first passive mode-locking of Cr:forsterite laser using a single-walled carbon nanotube saturable absorber (SWCNT-SA). The dispersion-compensated Cr:forsterite laser in a self-starting configuration produces nearly Fourier transform-limited pulses as short as 120 fs near 1.25 microm. The maximum average output power of 202 mW obtained with a 5% output coupler at a repetition rate of 79.1 MHz represents, to the best of our knowledge, the highest power level ever reported for SWCNT-SA mode locking of solid-state lasers.

Transmitting and reflecting ultrafast saturable absorbers based on single-walled carbon nanotubes are developed that are applicable for stable mode locking of bulk solid-state lasers operating near 1μm. For fabrication of these saturable absorbers, relatively simple spin coating and spray methods are employed. Parameters important for stable mode locking, such as transient nonlinear absorption, saturation fluence, and recovery time, are investigated by nonlinear transmission and time-resolved pump-probe measurements near 1μm. Typical modulation depths and recovery times amount to ∼0.21%–0.25% and

Different types of carbon nanotube saturable absorbers were fabricated and characterized. Their application for solid-state laser mode-locking enabled the generation of sub-100-fs pulses near 1.25 µm with powers up to 280 mW at 79 MHz.