V. E. Kisel

Broadly tunable femtosecond mode-locking in a Tm:KYW laser near 2 μm

Efficient mode-locking in a Tm:KY(WO(4))(2) laser is demonstrated by using InGaAsSb quantum-well SESAMs. Self-starting ultrashort pulse generation was realized in the 1979-2074 nm spectral region. Maximum average output power up to 411 mW was produced around 1986 nm with the corresponding pulse duration and repetition rate of 549 fs and 105 MHz respectively. Optimised pulse durations of 386 fs were produced with an average power of 235 mW at 2029 nm.

Passively Q-switched Er-Yb double-clad fiber laser with Cr2+:ZnSe and Co2+:MgAl2O4 as a saturable absorber

Here we report, for the first time to our knowledge, a cladding-pumped passively Q-switched Er-Yb codoped fiber laser with Cr2+:ZnSe and Co2+:MgAl2O4 as saturable absorbers. The maximum average output power for both crystals was 1.4 W, with typical pulse energy was 20 μJ corresponding to 60 W peak power. The pulse duration could be varied between 370 - 700 ns and repetition rate between 20 and 85 kHz by adjusting the pump power.

Semiconductor nanostructures modified by the UV laser radiation

The shortening of the absorption recovery time by a factor of more than 50 is observed for the semiconductor nanostructure consisting of ten GaAs/InxGa1-xAs/GaAs quantum wells irradiated with the nanosecond pulses of the XeCl laser.A possible reason for such a significant variation in the optical properties lies in the generation of point defects,which are responsible for recombination of charge carriers.The result can be employed in the UV photomodification of optical properties of semiconductor nanostructures.

Advances in femtosecond lasers having enhanced efficiencies

Progress in the development of efficient and reliable diode-pumped femtosecond laser systems based on both Kerr-lens and saturable-absorber mode locking is reported. Efficient Kerr-lens mode locking in diode pumped ytterbium-doped lasers, namely Yb:KY(WO4)2 (Yb:KYW) and Yb:YVO4, is demonstrated with average output powers in excess of 1W, pulse durations around 100fs and electrical-to-optical efficiencies that exceed 15%. Novel semiconductor saturable absorbers based on InAs/InGaAs quantum dots are described and their applicability for efficient femtosecond pulse generation from near-infrared solid-state lasers is discussed. Efficient passive mode locking in the spectral regions around 1.3&mgr;m and 1.55&mgr;m in Cr:forsterite and the more recently developed Er, Yb:YAl3(BO4)3 crystalline lasers has been demonstrated using low-loss InGaNAs saturable absorbers. A few examples of applications for this category of robust and efficient femtosecond lasers have been included. Specifically, the characteristics of a femtosecond visible light source producing pulses as short as 200fs at 520nm are outlined.

Efficient high-power femtosecond Yb3+:KY(WO4)2 laser

A stable mode-locking regime at a repetition rate of 70 MHz with 5 W average power, maximum output pulse energy of about 71 nJ, and pulse duration of 114 fs were obtained in an Yb:KY(WO4)2 laser with longitudinal off-axis diode pumping. Optical-to-optical laser efficiency was as high as 33.3%. A semiconductor saturable absorber including quantum wells with nanostructured barriers was designed and manufactured for this laser.

Self-mode-locking of the Nd3+:KGd(WO4)2 laser using a multifunctional semiconductor mirror

A multifunctional semiconductor mirror that contains a saturable absorber based on quantum wells, a broadband reflector, and a Gires-Tournois interferometer that serves as a GVD compensator is designed and created. The mirror is fully characterized using the pump-probe technique with a subpicosecond resolution and the transmission and photoluminescence spectroscopy. The mirror that simultaneously executes the three functions and that is created in a single technological cycle provides stable mode-locking in the Nd3+:KGd(WO4)2 laser.

Yb3+:KY(WO4)2 laser with a fast saturable absorber

Quantum-well semiconductor structures with superlattice barriers and reduced recovery time of absorption are designed and manufactured. A saturable absorption mirror based on such a structure is used in the Yb3+:KY(WO4)2 laser. The mode locking at a repetition rate of 70 MHz yields an almost bandwidth-limited pulse with a duration of about 115 fs. The maximum mean power (1.57 W) is comparable with a CW power of 1.62 W, which indicates a relatively low level of nonsaturable loss in the saturable absorption mirror.

Fast mirrors for femtosecond passive mode-locked near-infrared lasers

The design, manufacturing and characterization of the near infrared fast, low non-saturable loss semiconductor mirrors with saturable absorption based on InGaAs quantum wells separated by super-lattice GaAs/InGaAs barriers are analyzed from the viewpoints of recovery time shortening mechanism and of further improvement of mirror performance.

Semiconductor A3B5 nanostructures for infrared femtosecond lasers

Two techniques were suggested and tested for the recovery time shortening of saturable absorbers on a base of A3B5 compounds including quantum wells. The first one, proposed by authors, is the sample post-growth treatment by UV laser radiation; it implied generation of point defects, which, in its turn, led to electron-hole recombination acceleration and to recovery time shortening by an order of magnitude and more. Another technique based on special design of barriers gave promising results for the fast saturable absorbers. Semiconductor mirrors designed for Yb3+:KY(WO4)2 infrared laser mode locking led to 115 fs stable mode-locking regime with average power close to CW operation. Results on fast saturable absorbers for spectral region of 1500 nm are also presented.

Luminescent and lasing characteristics of heavily doped Yb{sup 3+}:KY(WO{sub 4}){sub 2} crystals

The luminescence decay times are measured taking into account reabsorption for KY(WO4)2:Yb(KYW:Yb) crystals with atomic concentrations of active ions from 0.2% to 30%. The radiative lifetime of Yb3+ ions was measured to be 233 μs. The cw output power of 1.46 and 1.62 W was achieved with the slope efficiency 52% and 47% for Yb:KYW lasers with the atomic concentration of Yb3+ ions equal to 10% and 30%, respectively. Using a semiconductor mirror with a saturable absorber (SESAM) in the passive mode-locking regime, pulses of duration 194 and 180 fs were obtained at wavelengths of 1042 and 1039 nm for crystals with Yb3+ concentrations equal to 10% and 30%, respectively, the average output power being 0.63 and 0.75 W.The luminescence decay times are measured taking into account reabsorption for KY(WO{sub 4}){sub 2}:Yb(KYW:Yb) crystals with atomic concentrations of active ions from 0.2% to 30%. The radiative lifetime of Yb{sup 3+} ions was measured to be 233 {mu}s. The cw output power of 1.46 and 1.62 W was achieved with the slope efficiency 52% and 47% for Yb:KYW lasers with the atomic concentration of Yb{sup 3+} ions equal to 10% and 30%, respectively. Using a semiconductor mirror with a saturable absorber (SESAM) in the passive mode-locking regime, pulses of duration 194 and 180 fs were obtained at wavelengths of 1042 and 1039 nm for crystals with Yb{sup 3+} concentrations equal to 10% and 30%, respectively, the average output power being 0.63 and 0.75 W. (lasers and amplifiers)