Gain characteristics of large volume CuBr laser active media

The paper presents the experimental results on how the active additive HBr and the temperatures of the containers with CuBr influence the gain characteristics of large volume (8 cm bore, 90 cm long) CuBr laser active media with the external heating of the active zone of the gas discharge tube (GDT). It has been demonstrated that an increase in the concentration of CuBr vapors results in the contraction of the gain profile of the active medium, consistent with the increase of the gain factor in the axial region of GDT. The contraction is also imposed by HBr addition. Despite the fact that we used the external heating of GDT at the pump power of 1.5 kW and less, the energy input is still not sufficient to produce the effective generation for large active volume lasers; and it is evident from the small gain profile width. The maximum gain profile width under experimental conditions (consider P_out/P_in > 2) was 3 cm; this value was obtained without HBr-additive within the active volume, while the concentration of CuBr vapors being significantly less than optimal, that corresponds to the maximum average lasing power.     

Supercontinuum broadening in all-normal dispersion photonic crystal fiber by means of soliton compression in standard single-mode fiber

Using standard single-mode fiber as high-order soliton compressor for broadening supercontinuum in an 80 m long all-normal dispersion photonic crystal fiber is investigated experimentally and numerically. An analytical formula for calculating proper fiber input power to generate the broadest supercontinuum is derived. The numerical results show that the formula is more accurate in high power level corresponding to the soliton order which is larger than two. The measured supercontinuum ? 20 dB bandwidth is broadened from 84.2 nm to 277.1 nm by using a 20 m long standard single-mode fiber without enhancing fiber input power. Numerical calculations of the amplitude noise in the output spectra show that using soliton compression effect can efficiently broaden the spectral bandwidth and not generate obvious noises.     

330 MHz,sub 50 fs Yb: Fiber ring laser

We demonstrate 330 MHz repetition rate operation in a ring cavity Yb:fiber laser with an innovative wavelength-division-multiplexing collimator to raise the repetition rate. The spectral bandwidth of the pulse is 30 nm and the dechirped pulse width is 48 fs. The output power is 70 mW with 600 mW, 975 nm pump laser diode.     

Efficient end-pumped Q-switched 1053 nm Nd:YLF laser with a plane-parallel resonator

In this study, a compact and efficient Nd:YLF laser at 1053 nm has been reported without inserting optical intracavity element to suppress the stronger line of 1047 nm. According to theoretical analysis and calculation, the thermal focal length of 1047 nm is negative while that of 1053 nm is positive in plane-parallel resonator. Hence 1053 nm laser was stable in this cavity. In our experiment, 7.5 W laser output at σ-polarized 1053 nm has been obtained with optical–optical efficiency of 38.8%. As the pulse repetition rate is 20 kHz, the pulse width is 50 ns and the peak power is calculated to be 7.5 kW.     

Ultra-broad and flat supercontinuum generation in short photonic crystal fiber combined with conventional fibers

In order to gain ultra-broad and flat super-continuum (SC) spectrum, we propose and demonstrate a new scheme. By coupling a train of short pulses with 100 fs width and 16.2 mW average power generated by a mode-locked laser into the scheme – short photonic crystal fiber (PCF) combined with conventional fibers. The SC spectrum has 491 nm bandwidth at −15 dBm below the spectral peak with ±0.5 dBm uniformity 100 nm in only 0.45 m PCF. The spectral bandwidth generated in the scheme increases 292 nm than spectrum generated in the two conventional fibers, and increases 152 nm than spectrum generated in the three convention fibers.     

Analysis of the spectral structure of CuBr laser lines

The spectral structure of spontaneous emission of copper atom at 510.6 nm and 578.2 nm was calculated considering the hyperfine structure of energy levels and the isotope shift. The spectral structure of the 510.6 nm and 578.2 nm laser lines was measured in a sealed-off CuBr laser tube with periodic refreshment of the neon buffer gas under different work temperature and excited voltage. The spectral structure of the spontaneous emission of copper atom was found to have similar outline with its laser lines. The spectrum of the 510.6 nm laser line maintains similar outline with three peaks at various discharging parameters while the spectrum of the 578.2 nm laser line is strongly dependent on the reservoir temperature and the discharge voltage.     

A 980 nm Yb-doped single-mode fiber laser pumped by a 946 nm Q-switched Nd:YAG laser

We demonstrate a 980 nm single-mode Yb-doped fiber laser with a 946 nm Q-switched Nd:YAG laser used as the pump source. The experimental arrangement exploited a 36.5 cm length of fiber and used the output from both ends of the cavity, providing a total average output power of 100 mW with a slope efficiency of 38%. In order to increase the coupling efficiency and the practicability of the fiber laser, another experimental setup with single ended output was studied, producing an average output power of 80 mW from a fiber length of 23.5 cm. The pulse duration is 10 ns at a repetition frequency of 16 kHz. The linewidth of the laser is 4 nm, ranging from 977 to 981 nm.     

A study on wavelength dependence and dynamic range of the quadratic response of commercial grade light emitting diodes

Experimental results of a study on the wavelength dependence and the dynamic range of the quadratic response of commercial grade light emitting diodes (LEDs) are reported over a broad spectral range of 680 nm to 1080 nm using ~ 100 fs duration laser pulses from cw mode locked laser oscillator. A large dynamic range of the quadratic response has been demonstrated in a reverse biased LED. The observed dynamic range compares well with that obtained using a biased photomultiplier tube with large internal gain.     

Optimization of microcrystalline silicon thin film solar cell isolation processing parameters using ultraviolet laser

This study used ultraviolet laser to perform the microcrystalline silicon thin film solar cell isolation scribing process, and applied the Taguchi method and an L₁₈ orthogonal array to plan the experiment. The isolation scribing materials included ZnO:Al, AZO transparent conductive film with a thickness of 200 nm, microcrystalline silicon thin film at 38% crystallinity and of thickness of 500 nm, and the aluminum back contact layer with a thickness of 300 nm. The main objective was to ensure the success of isolation scribing. After laser scribing isolation, using the minimum scribing line width, the flattest trough bottom, and the minimum processing edge surface bumps as the quality characteristics, this study performed main effect analysis and applied the ANOVA (analysis of variance) theory of the Taguchi method to identify the single quality optimal parameter. It then employed the hierarchical structure of the AHP (analytic hierarchy process) theory to establish the positive contrast matrix. After consistency verification, global weight calculation, and priority sequencing, the optimal multi-attribute parameters were obtained. Finally, the experimental results were verified by a Taguchi confirmation experiment and confidence interval calculation. The minimum scribing line width of AZO (200 nm) was 45.6 μm, the minimum scribing line width of the microcrystalline silicon (at 38% crystallinity) was 50.63 μm and the minimum line width of the aluminum thin film (300 nm) was 30.96 μm. The confirmation experiment results were within the 95% confidence interval, verifying that using ultraviolet laser in the isolation scribing process for microcrystalline silicon thin film solar cell has high reproducibility.     

Numerical analysis of a broadband spectrum generated in a standard fiber by noise-like pulses from a passively mode-locked fiber laser

This paper covers a numerical analysis of supercontinuum spectrum generation in a piece of standard fiber by using as the pump noise-like pulses produced by a passively mode-locked fiber laser. An experimental study was also carried out, yielding results that support the numerical results. In the numerical study we estimated that the spectral extension of the generated supercontinuum reaches ~ 1000 nm, and that it presents a high flatness over a region of ~ 220 nm (1630 nm-1850 nm) when we use as the pump noise-like pulses with a wide optical bandwidth (~ 50 nm) and a peak power of ~ 2 kW. Experimentally, the output signal spectrum extends from ~ 1530 nm to at least 1750 nm and presents a high flatness over a region of 1640 nm to 1750 nm for the same value of numerical input power, 1750 nm being the upper limit of the optical spectrum analyzer. The numerical analysis presented here is thus an essential part to overcome the severe limitation in measuring capabilities and to understand the phenomena of supercontinuum generation, which is mainly related to Raman self-frequency shift. Finally, this work demonstrates the potential of noise-like pulses from a passively mode-locked fiber laser for broadband spectrum generation.     

Pump tuned wide tunable noncritically phase-matched ZnGeP2 narrow line width optical parametric oscillator

A line tunable singly resonant noncritically phase matched narrow band width ZnGeP₂ (ZGP) optical parametric oscillator pumped by the output idler radiation from a KTA OPO based on a 20 mm long KTA crystal pumped from a Q-switched Gaussian shaped Nd:YAG laser beam with a grating having grooves density 85 lines/mm has been demonstrated in the spectral ranges of 3–7 μm. The measured threshold of oscillation energy was 10 μJ. The conversion efficiency was 20.5% and slope efficiency of the ZGP OPO was 20% using a 23 mm long ZGP crystal at 26 mm cavity length. Line width of the generated infrared radiation from ZGP OPO was 37–60 nm.     

Passively Q-switched a-cut Nd:GdVO4 self-Raman laser with Cr:YAG

A passively Q-switched a-cut Nd:GdVO₄ self-Raman solid-state laser with Cr:YAG saturable absorber was firstly demonstrated. The first Stokes at 1173 nm was successfully obtained. At the maximum incident pump power, the pulse width was about 1.8 ns and the repetition rate was 27.5 kHz. 586.5 nm yellow laser output was also realized by use of an LBO frequency doubling crystal.     

Wide-band fanned-out supercontinuum source covering O-, E-, S-, C-, L- and U-bands

A wide-band supercontinuum source generated by mode-locked pulses injected into a Highly Non-Linear Fiber (HNLF) is proposed and demonstrated. A 49 cm long Bismuth–Erbium Doped Fiber (Bi–EDF) pumped by two 1480 nm laser diodes acts as the active gain medium for a ring fiber laser, from which mode-locked pulses are obtained using the Non-Polarization Rotation (NPR) technique. The mode-locked pulses are then injected into a 100 m long HLNF with a dispersion of 0.15 ps/nm km at 1550 nm to generate a supercontinuum spectrum spanning from 1340 nm to more than 1680 nm with a pulse width of 0.08 ps and an average power of ?17 dBm. The supercontinuum spectrum is sliced using a 24 channel Arrayed Waveguide Grating (AWG) with a channel spacing of 100 GHz to obtain a fanned-out laser output covering the O-, E-, S-, C-, L- and U-bands. The lasing wavelengths obtained have an average pulse width of 9 ps with only minor fluctuations and a mode-locked repetition rate of 40 MHz, and is sufficiently stable to be used in a variety of sensing and communication applications, most notably as cost-effective sources for Fiber-to-the-Home (FTTH) networks.     

Cr4+:YAG passively Q-switched c-cut Nd:YVO4 self-Raman laser at 1168.6 nm

We demonstrate the first Cr⁴⁺:YAG passively Q-switched c-cut Nd:YVO₄ self-Raman laser at 1168.6 nm based on the Stokes shift of 816 cm⁻¹. At the pump power of 4.7 W, the maximum output power of the Stokes line at 1168.6 nm is 270.5 mW, corresponding to an optical conversion efficiency of 5.8%. The pulse width, pulse repetition rate, pulse energy and peak power are 8.8 ns, 35.8 kHz, 7.6 μJ and 0.86 kW, respectively. At the pump of 5.0 W, the Stokes line at 1097.2 nm based on Raman shift of 259 cm⁻¹ also appears.     

Low-threshold continuous-wave Tm3+:YAlO3 laser

We describe a continuous-wave, low-threshold Tm:YAlO₃ (Tm:YAP) laser operating at 1945 nm with incident threshold pump powers in the 10–20 mW range. The z-cavity containing a 2-mm-long Tm:YAP crystal with 4 at.% Tm³⁺ concentration was end pumped by a continuous-wave Ti:sapphire laser at 795 nm. Tight focusing of the pump and the laser beams enabled low-threshold operation. The power performance of two different cavity configurations with 5-cm radius (R = 5 cm cavity) and 10-cm radius (R = 10 cm cavity) curved mirrors was tested. The best performance was obtained with the R = 10 cm configuration, where, the incident threshold pump power could be lowered to 10 mW after optimizing the polarization direction of the pump beam and by employing double pumping. Theoretical estimation of the threshold power was in good agreement with the experimental observations. The laser could be further tuned from 1842 to 1994 nm.     

A compact continuous-wave green laser with line beam for laser projection

An efficient and compact continuous-wave green laser with line beam using LBO crystal was developed. The maximum output power was 6.5 W. The optical-to-optical conversion efficiency was as high as 31%. The compact size of the line beam green laser was 2 cm×5 cm×8.8 cm. Reliability and stability of the green laser were evaluated.     

980 nm Yb-doped double-clad photonic crystal fiber amplifier and its frequency doubling

In this paper, we report on a large-mode-area double-clad 980 nm Yb-doped photonic crystal fiber (PCF) amplifier. In the experiment, an output power of 1.21 W at 980 nm with 2.5 nm bandwidth has been yielded when the PCF length was 40 cm. Through frequency doubling the 980 nm amplified laser with a BIBO crystal, an output power of 51 mW at 490 nm has been generated.     

A beam shaping design for coupling high power diode laser stack to fiber with capability of spectral narrowing and stabilizing

We applied a VHG-FAC lens in our design in this work to collimate the fast axis and lock the output spectrally. We used a beam shaping technique to improve the beam symmetry and power density of a high power diode laser stack with a stripe mirror plate, a V-Stack mirror and polarization beam combining elements. By this technique, the beam of a high power diode laser stack is effectively coupled into a standard 365 μmcore diameter and a NA = 0.22 fiber. By this technique, compactness, higher efficiency, narrower spectral line width and lower production cost of the diodes are possible.     

Tunable dual-wavelength fiber laser based on an opto-VLSI processor and four-wave mixing in a photonic crystal fiber

A stable wavelength and wavelength spacing tunable dual-wavelength fiber laser based on an Opto-very-large-scale-integration (Opto-VLSI) processor and four-wave mixing (FWM) in a high-nonlinear photonic crystal fiber is experimentally demonstrated. The results show that the line width of the tunable dual-wavelength fiber laser is 0.02 nm, and the wavelength spacing can be tuned from 0.8 nm to 4 nm with a 0.15 nm step. Under the influence of the FWM, the uniformity is below 0.6 dB and the measured side mode suppression ratio (SMSR) is above 45 dB.     

60 W yellow laser at 561 nm by intracavity frequency doubling of a diode-pumped Q-switched Nd:YAG laser

A high-power yellow laser was achieved by intracavity frequency doubling of a diode-pumped Nd:YAG rod laser. A solid etalon was inserted into the resonator to implement efficient operation of the low-gain single line at 1123 nm transition. By using a LBO crystal inside the cavity as the frequency doubler, the maximum output power of the 561 nm yellow laser was obtained to be as high as 60.3 W with a pulse repetition frequency of 6 kHz, corresponding to an optical-to-optical conversion efficiency of about 6.1%. The output power fluctuation of the yellow laser was measured to be better than 3% in half an hour.