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.
A buried depressed-index channel waveguide with a circular cladding and a core diameter of 40 μm is fabricated in a bulk monoclinic 3 at.% Tm:KLu(WO4)2 crystal by femtosecond direct laser writing. In the continuous-wave regime, the Tm waveguide laser generates ∼210 mW at 1849.6 nm with a slope efficiency η of 40.8%. Passively Q-switched operation is achieved by inserting transmission-type 2D saturable absorbers (SAs) based on few-layer graphene and MoS2. Using the graphene-SA, a maximum average output power of ∼25 mW is generated at 1844.8 nm. The pulse characteristics (duration/energy) are 88 ns/18 nJ at a repetition rate of 1.39 MHz.
We demonstrate a passively Q-switched Yb3+-dopedScBO3 bulk laser using a black phosphorous (BP) saturable absorber, a two-dimensional semiconductor. The response spectra of BP show that it is suitable as a universal switcher in the spectral range from the visible to midinfrared band. Considering the saturable absorption properties of BP and emission properties of Yb3+-doped crystals, the passively Q-switched bulk laser pulses were realized with the Yb3+:ScBO3 crystal as a gain material and a fabricated BP sample as a Q-switcher. Because of the large energy storage capacity of Yb3+:ScBO3, the maximum output energy is obtained to be 1.4 μJ, which is comparable with the previous reported maximum energy of graphene Q-switched lasers. The obtained results identify the potential capability of BP as a pulse modulator in bulk lasers, and BP plays an increasingly important role in a wide range of its applications, including photonics and optoelectronics.
In this paper, we report an abnormal laser deflection phenomena based on quadratic electro-optic effect in copper doped KTN crystal. Cu:KTa0.62Nb0.38O3 block with size a×b×c = 2.8mm×2.6mm×12.5mm was used as beam deflection element. 75mrad beam deflection angle were observed under 1KV voltage when the laser beam across the c direction of the sample at room temperature. The special features of our experiment are that the direction of laser beam deflect perpendicular to the electric field direction, and the angular size and direction of the deflection beam remain unchanged when the electric field direction reverse. We believe that the interaction of graded refractivity and electro-optic effect leads to these special features. Besides of the special deflection mode, the deflection efficiency of our experiment also reached the world advanced level.
A new series Er:LuxGd1-xVO4 (x=0.1，0.24，0.48，0.57，0.79 and 0.9)mixed laser crystals have been successfully grown by the Czochralski method with 1% Er3+ concentration.The thermal properties of Er:LuxGd1-xVO4crystals series crystals were investigated systematically, including the thermal expansion, specific heat, thermal diffusion coefficients, and thermal conductivities. The anisotropy and variation of the thermal properties with the component x were also achieved and discussed based on their structure. All the results showed that this mixed crystals should have promising applications in the moderate-power lasers.
We demonstrate passive Q-switching (PQS) of the Tm-doped BaY2F8 (Tm:BYF) laser for the first time. The Tm:BYF
laser is diode-pumped using an L-shaped hemispherical resonator. In the cw regime, the maximum output power with an
18% Tm-doped BYF crystal reached 1.12 W at ~1920 nm for an absorbed pump power of 3.06 W. In the PQS regime,
maximum pulse energy (720 μJ) and peak power (17.1 kW) were obtained with an 8% Tm-doped BYF crystal and a
Cr:ZnS saturable absorber with 92% low-signal transmission, again near 1920 nm, for a pulse width of ~40 ns and a
repetition rate of 50 Hz.
A high power passive Q-switched laser and a continuous-wave (CW) green laser both with a neodymium-doped yttrium aluminum garnet (Nd:YAG) ceramic as the laser material have been demonstrated. Two Cr4+:YAG crystals with 73.9% and 79.6% initial transmission at 1064 nm have been used as saturable absorbers. In Q-switched regime the laser generated up to 209 μJ, 4.5 ns pulses, which corresponds to a peak power of 46.8 kW. In CW regime at 1064 nm the laser generated 11.3 W of output power at a pump power of 21.6 W, corresponding to an optical-optical conversion efficiency of 52.3%. By using a type-II cut KTP crystal, the CW frequency-doubled operation of Nd:YAG ceramic was achieved. The maximum output power of 1.86 W at 532 nm has been obtained. The one-dimensional intensity distribution of the green beam cross-section was observed to be Gaussian. When the output power was 1 W, the M2 factor was measured to be 1.7.