Interferometric optical path difference measurement using sinusoidal frequency modulation of a diode laser

We describe a technique applicable to interferometric systems illuminated by a laser diode, whereby the optical path difference is recovered by means of sinusoidal modulation of the laser emission frequency.

Optimization of erbium-doped actively Q-switched fiber laser implemented in symmetric configuration

We report the results of an experimental study aimed at improving the performance of actively Q-switched fiber lasers. Unlike generic design schemes employing photonic crystal fibers, largemodal diameter fibers or double-clad fibers, we demonstrate a high-power, actively Q-switched laser based on standard com- munication erbium doped fibers with peak irradiance beyond the state-of-the-art at 3.1 GW/cm2 . The laser had 2.2 kW peak power, 15.5 ns pulse duration and 36.8 µJ pulse energy. We have also investigated the dynamics of pulse generation and have success- fully suppressed pulse instabilities caused by backscattered laser emission reaching the pump laser diodes.

Multi-kilowatt peak power nanosecond Er-doped fiber laser

We report a two-stage diode-pumped Er-doped fiber amplifier operating at the wavelength of 1550 nm at the repetition rate of 10-100 kHz with an average output power of up to 10 W. The first stage comprising Er-doped fiber was core-pumped at the wavelength of 1480 nm, whereas the second stage comprising double-clad Er/Yb-doped fiber was clad-pumped at the wavelength of 975 nm. The estimated peak power for the 0.4-nm full-width at half-maximum laser emission at the wavelength of 1550 nm exceeded 4-kW level. The initial 100-ns seed diode laser pulse was compressed to 3.5 ns as a result of the 34-dB total amplification. The observed 30-fold efficient pulse compression reveals a promising new nonlinear optical technique for the generation of high power short pulses for applications in eye-safe ranging and micromachining.

Two different operation regimes of fiber laser based on nonlinear polarization rotation : passive mode-locking and multiwavelength emission

We have proposed and demonstrated a nonlinear polarization-rotation-based fiber laser with two different operation states: passive mode-locking and multiwavelength emission. The intensity-dependent transmission or loss induced by nonlinear polarization rotation accounts for the distinct operation regimes. Our experiment results indicate that both passively mode-locked pulses and continuous-wave multiwavelength can be generated from the same fiber laser just through adjusting polarizations. Another characteristic of the current multiwavelength laser is that the used periodic filter is a birefringence fiber filter, which facilitates all-fiber integration of the fiber laser, so it is a potential multifunction laser source with all-fiber configuration and convenient manipulation. © 2008 IEEE.

Two different operation regimes of fiber laser based on nonlinear polarization rotation:passive mode-locking and multiwavelength emission

We have proposed and demonstrated a nonlinear polarization-rotation-based fiber laser with two different operation states: passive mode-locking and multiwavelength emission. The intensity-dependent transmission or loss induced by nonlinear polarization rotation accounts for the distinct operation regimes. Our experiment results indicate that both passively mode-locked pulses and continuous-wave multiwavelength can be generated from the same fiber laser just through adjusting polarizations. Another characteristic of the current multiwavelength laser is that the used periodic filter is a birefringence fiber filter, which facilitates all-fiber integration of the fiber laser, so it is a potential multifunction laser source with all-fiber configuration and convenient manipulation. © 2008 IEEE.

THz emission from quantum dot-based THz antennas pumped by a tunable quantum-dot laser diode

The THz optoelectronics field is now maturing and semiconductor-based THz antenna devices are becoming more widely implemented as analytical tools in spectroscopy and imaging. Photoconductive (PC) THz switches/antennas are driven optically typically using either an ultrashort-pulse laser or an optical signal composed of two simultaneous longitudinal wavelengths which are beat together in the PC material at a THz difference frequency. This allows the generation of (photo)carrier pairs which are then captured over ultrashort timescales usually by defects and trapping sites throughout the active material lattice. Defect-implanted PC materials with relatively high bandgap energy are typically used and many parameters such as carrier mobility and PC gain are greatly compromised. This paper demonstrates the implementation of low bandgap energy InAs quantum dots (QDs) embedded in standard crystalline GaAs as both the PC medium and the ultrafast capture mechanism in a PC THz antenna. This semiconductor structure is grown using standard MBE methods and allows the device to be optically driven efficiently at wavelengths up to ~1.3 µm, in this case by a single tunable dual-mode QD diode laser.

Gamma-shaped long-cavity normal-dispersion mode-locked Er-fiber laser for sub-nanosecond high-energy pulsed generation

We propose the design of a novel ?-shaped fiber laser resonator and apply it to build a long-cavity normaldispersion mode-locked Er-fiber laser which features enhanced functionalities for management and optimization of pulsed lasing regimes. We report the generation of sub-nanosecond pulses with the energy of ~0.5 µJ at a kilohertz-scale repetition rate in an all-fiber system based on the new laser design. A combination of special design solutions in the laser, such as polarization instability compensation in the ultra-long arm of the resonator, intra-cavity spectral selection of radiation with a broadband fiber Bragg grating, and polarization selection by means of a tilted refractive index grating, ensures low amplified spontaneous emission (ASE) noise and high stability of the laser system output parameters.

Tuned cascade laser

Tuning of a diode-cladding-pumped cascade Ho3+ -doped fluoride fiber laser is demonstrated using a single plane ruled diffraction grating. At the maximum available pump power, a tuning range 2955-3021 nm, an output power of >500 mW, and a bandwidth of <1nm was achieved for tuning across the 5|6 -> 5|7 transition. In a separate experiment, the  5|7 -> 5|8 laser transition was tuned from 2064 to 2082 nm (with a bandwidth of <0.5 nm) which simultaneously shortened the average emission wavelen 5|6 -> 5|7 length of the free-running  laser transition of the cascade from 2.959 to 2.954 µm. This demonstration represents the first fiber laser that can tune beyond 3 µm.

Gamma-shaped long-cavity normal-dispersion mode-locked Er-fiber laser for sub-nanosecond high-energy pulsed generation

We propose the design of a novel ?-shaped fiber laser resonator and apply it to build a long-cavity normaldispersion mode-locked Er-fiber laser which features enhanced functionalities for management and optimization of pulsed lasing regimes. We report the generation of sub-nanosecond pulses with the energy of ~0.5 µJ at a kilohertz-scale repetition rate in an all-fiber system based on the new laser design. A combination of special design solutions in the laser, such as polarization instability compensation in the ultra-long arm of the resonator, intra-cavity spectral selection of radiation with a broadband fiber Bragg grating, and polarization selection by means of a tilted refractive index grating, ensures low amplified spontaneous emission (ASE) noise and high stability of the laser system output parameters.

1.2-μm semiconductor disk laser frequency doubled with periodically poled lithium tantalate crystal

In this letter, we demonstrate an optically pumped semiconductor disk laser frequency doubled with a periodically poled lithium tantalate crystal. Crystals with various lengths were tested for intracavity frequency conversion. The semiconductor disk laser exploited GaInNAs-based active region with GaAsAlAs distributed Bragg mirror to produce emission at 1.2- μm wavelength. The frequency doubled power up to 760 mW at the wavelength of 610 nm was achieved with a 2-mm-long crystal. © 2010 IEEE.

Multimodal spectral control of a quantum-dot diode laser for THz difference frequency generation

Generation of stable dual and/or multiple longitudinal modes emitted from a single quantum dot (QD) laser diode (LD) over a broad wavelength range by using volume Bragg gratings (VBG's) in an external cavity setup is reported. The LD operates in both the ground and excited states and the gratings give a dual-mode separation around each emission peak of 5 nm, which is suitable as a continuous wave (CW) optical pump signal for a terahertz (THz) photomixer device. The setup also generates dual modes around both 1180m and 1260 nm simultaneously, giving four simultaneous narrow linewidth modes comprising two simultaneous difference frequency pump signals. (C) 2011 American Institute of Physics.

Narrow-band generation in random distributed feedback fiber laser

Narrow-band emission of spectral width down to ∼0.05 nm linewidth is achieved in the random distributed feedback fiber laser employing narrow-band fiber Bragg grating or fiber Fabry-Perot interferometer filters. The observed line-width is ∼10 times less than line-width of other demonstrated up to date random distributed feedback fiber lasers. The random DFB laser with Fabry-Perot interferometer filter provides simultaneously multi-wavelength and narrow-band (within each line) generation with possibility of further wavelength tuning. © 2013 Optical Society of America.

High-power quantum-dot vertical-external-cavity surface-emitting laser exceeding 8 W

We report on a record-high output power from an optically pumped quantum-dot vertical-external-cavity surface-emitting laser, optimized for high-power emission at 1040 nm. A maximum continuous-wave output power of 8.41 W is obtained at a heat sink temperature of 1.5 °C. By inserting a birefringent filter inside the laser cavity, a wavelength tuning over a range of 45 nm is achieved. © 2014 IEEE.

Defects in ZnO nanoparticles laser-ablated in water-ethanol mixtures at different pressures

The effect of liquid medium and its pressure on the photoluminescence of ZnO nanoparticles prepared via laser ablation of Zn targets in various water-ethanol mixtures is studied. As the ethanol content increases, the photoluminescence of the product changes, while metallic zinc is observed to emerge in nanomaterials prepared in ethanol-rich environments. The applied pressure had a less profound effect, mainly affecting materials produced in water or water-ethanol, and much less those generated in pressurized ethanol. Tuning the reactivity of the liquid and pressurizing it during laser ablation is demonstrated to be promising for tailoring the emission properties of the product.

Optical trapping with superfocused high-M2 laser diode beam

Many applications of high-power laser diodes demand tight focusing. This is often not possible due to the multimode nature of semiconductor laser radiation possessing beam propagation parameter M2 values in double-digits. We propose a method of 'interference' superfocusing of high-M2 diode laser beams with a technique developed for the generation of Bessel beams based on the employment of an axicon fabricated on the tip of a 100 μm diameter optical fiber with highprecision direct laser writing. Using axicons with apex angle 140º and rounded tip area as small as 10 μm diameter, we demonstrate 2-4 μm diameter focused laser 'needle' beams with approximately 20 μm propagation length generated from multimode diode laser with beam propagation parameter M2=18 and emission wavelength of 960 nm. This is a few-fold reduction compared to the minimal focal spot size of 11 μm that could be achieved if focused by an 'ideal' lens of unity numerical aperture. The same technique using a 160º axicon allowed us to demonstrate few-μm-wide laser 'needle' beams with nearly 100 μm propagation length with which to demonstrate optical trapping of 5-6 μm rat blood red cells in a water-heparin solution. Our results indicate the good potential of superfocused diode laser beams for applications relating to optical trapping and manipulation of microscopic objects including living biological objects with aspirations towards subsequent novel lab-on-chip configurations.