Pulsed erbium fiber laser with an acetylene-filled photonic crystal fiber for saturable absorption

We investigate the dynamics of an erbium-doped fiber ring laser that is equipped with an intracavity hollow core photonic crystal fiber gas cell. The cell is filled with acetylene as a saturable absorber. We observe cw operation at low pressures, Q switching at intermediate pressure levels, and mode locking at high pressures applied. Moreover, we show that the transition from the cw to the pulsed mode may be exploited for sensitive gas detection.     

Generation of 5-W deep-UV continuous-wave radiation at 266 nm by an external cavity with a CsLiB6O10 crystal

A Brewster-cut CsLiB6O10 crystal is employed as an external resonant frequency doubler to generate cw deep-UV radiation at 266 nm. We have generated 5.0 W of usable cw output power, which is 6.1 W in the crystal, for an incident green power of 9.6 W, corresponding to an internal conversion efficiency of 61.8%. The power obtained is, to our knowledge, three times higher than previously reported for cw 266-nm generation.     

Multicrystal, continuous-wave, single-pass second-harmonic generation with 56% efficiency

We report a simple and compact implementation for single-pass second-harmonic-generation (SP-SHG) of cw laser radiation, based on a cascaded multicrystal (MC) scheme, that can provide the highest conversion efficiency at any given fundamental power. By deploying a suitable number of identical 30-mm-long MgO:sPPLT crystals in a cascade and a 30W cw Yb-fiber laser at 1064nm as the fundamental source, we demonstrate SP-SHG into the green with a conversion efficiency as high as 56% in the low-power as well as the high-power regime, providing 5.6W of green output for 10W and 13W of green output for 25.1W of input pump power. The MC scheme permits substantial increase in cw SP-SHG efficiency compared to the conventional single-crystal scheme without compromising performance with regard to power stability and beam quality.     

Frequency-modulation-mode-locked optical parametric oscillator

We demonstrate a novel technique for the generation of mode-locked pulses from a continuous-wave (cw) optical parametric oscillator (OPO). The technique is based on the deployment of a phase modulator in combination with an antiresonant ring interferometer internal to a cw OPO, simultaneously providing spectral broadening and phase-to-amplitude feedback modulation. The scheme is implemented in a doubly-resonant cw OPO based on MgO:sPPLT, configured in a standing-wave cavity and pumped at 532 nm. With the phase modulator activated and the cavity length synchronized, a stable train of 800 ps pulses is generated at a repetition rate of 160 MHz. Using single-pass second harmonic generation (SHG) of the OPO output, we observe a four times enhancement in SHG compared with cw operation, confirming the real achievement of energy concentration as a result of mode-locked operation.     

Continuous-wave laser at 440 nm based on frequency-doubled diode-pumped Nd:GdVO(4) crystal

We present for the first time, to the best of our knowledge, a frequency-doubled Nd:GdVO(4) laser operating in a cw on the pure three-level laser line at 880 nm. We obtained 300 mW at 440 nm for 23 W of incident pump power at 808 nm. Moreover, with a 25% output coupler we obtained a cw power of 1.9 W at the fundamental wavelength at 880 nm.     

Self modulation phenomena in an external-cavity semiconductor laser

We report the observed self-modulation phenomena in an external-cavity semiconductor laser, in which a slant ridge-loading waveguide was formed for the gain medium. A region beside the ridge at a cleaved end of the waveguide served as a saturable absorber for self-modulation. Under different conditions of injection current and cavity alignment, we observed three laser operation regimes, including pure cw oscillation, constant-amplitude pulse-like signal on the top of a cw component, and amplitude-modulated pulse-like signal coexistent with a cw component. The amplitude modulation phenomenon is different from the previously reported concurrence of mode-locking and self-pulsation. A model was proposed to explain the observed results.     

A continuous wave SrMoO4 Raman laser

We demonstrate a cw, laser diode-pumped Nd:GdVO4/SrMoO4 crystalline Raman laser. First Stokes laser output at 1173.5?nm of 2.18?W was achieved with a diode-to-first Stokes efficiency of 8.7%. With intracavity frequency doubling in LiB3O5, 3.1?W of cw yellow emission at 586.8?nm was obtained with a 12.4% diode-to-yellow efficiency. The experimental results show that SrMoO4 is an excellent stimulated Raman scattering gain material for high-power cw near-IR Stokes and yellow lasers.     

Self-switching of optical pulses in dispersion-imbalanced nonlinear loop mirrors

We report a novel nonlinear filter that transmits and shortens incident pulses while rejecting cw background as well as resonant continuum. A relative extinction of 22dB is reported for the cw background.     

Passively Mode-Locked Quasi-Three-Level Nd:LuVO4Laser with Semiconductor Saturable Absorber Mirror

We demonstrate a passively a Z-folded resonator. Using device, we achieve stable cw average output power under cw mode-locked Nd：LuVO4 laser operating on the quasi-three-level at 916nm with a semiconductor saturable absorber mirror （SESAM） as the passive mode-locking mode locking with 6.7ps pulse duration at repetition rate of 133 MHz and 88mW the pump power of 17.1 W.     

Diode-pumped Nd:GAGG-LBO laser at 531 nm

We report a green laser at 531 nm generation by intracavity frequency doubling of a continuous wave (cw) laser operation of a 1062 nm Nd:GAGG laser under in-band diode pumping at 808 nm. A LiB₃O₅ (LBO) crystal, cut for critical type I phase matching at room temperature is used for second harmonic generation of the laser. At an incident pump power of 18.5 W, as high as 933 mW of cw output power at 531 nm is achieved. The fluctuation of the green output power was better than 3.5% in the given 4 h.     

Passively Q-switched microchip Er, Yb:YAl3(BO3)4 diode-pumped laser

We report, for the first time to our knowledge, a diode-pumped cw and passively Q-switched microchip Er, Yb:YAl(3)(BO(3))(4) laser. A maximal output power of 800 mW at 1602 nm in the cw regime was obtained at an absorbed pump power of 7.7 W. By using Co(2+):MgAl(2)O(4) as a saturable absorber, a TEM(00)-mode Q-switched average output power of 315 mW was demonstrated at 1522 nm, with pulse duration of 5 ns and pulse energy of 5.25 μJ at a repetition rate of 60 kHz.     

Highly efficient, low-cost femtosecond Cr3+ :LiCAF laser pumped by single-mode diodes

We describe efficient continuous-wave (cw) and cw mode-locked operations of a Cr3+ :LiCAF laser, pumped by inexpensive single spatial mode laser diodes. Up to 280 mW of cw output power was obtained with 570 mW of absorbed pump power, with a corresponding slope efficiency of 54%. Continuous tuning between 765 and 865 nm was demonstrated using a fused silica prism. A semiconductor saturable absorber mirror was used to initiate and sustain stable, self-starting, mode-locked operation. In cw mode locking, the laser produced 72 fs (FWHM) duration pulses, and 1.4 nJ pulse energy, at an average output power of 178 mW. Electrical to optical conversion efficiencies of 7.8% in mode-locked operation and 12.2% in cw operation were demonstrated.     

Diode-pumped Nd:LGS/LBO laser at 452 nm

We report a blue laser at 452 nm generation by intracavity frequency doubling of a continuous wave (cw) laser operation of a 904 nm Nd:LGS laser under 808 nm diode pumping. A LiB₃O₅ (LBO) crystal, cut for critical type I phase matching at room temperature is used for second harmonic generation (SHG) of the laser. At an incident pump power of 17.8 W, as high as 1.14 W of cw output power at 452 nm is achieved. The optical-to-optical conversion efficiency is up to 6.4%, and the fluctuation of the blue output power was better than 4.1% in the given 30 min.     

Stable passively Q-switched operation of Tm3+ doped silica fiber laser by anti-resonant Fabry-Perot saturable absorber

We demonstrate a diode-pumped passively Q-switched Tm-doped double-cladding silica fiber laser operating at wavelength of 1960 nm using an anti-resonant Fabry-Perot saturable absorber as passive modulation element. To determine a relatively preferable fiber length for stable cw Q-switched operation, three active fiber simples with the length of 1.1, 5.3, and 7.0 m were employed respectively in our experiments. With 1.1 m gain fiber, we generated Q-switched pulses with a pulse width of 245 ns and an average power of up to 2.2 W at a repetition rate of 620 kHz. For the longer two fiber samples, Q-switched operation with longer pulse duration, Q-switched mode-locking and cw mode-locking were observed, respectively.     

Chlorotetracycline-induced fluorescence from atherosclerotic plaque with uv laser excitation

We have investigated the fluorescence from post mortem atherosclerotic and normal aortic valve segments and coronary arteries induced by pulsed and cw lasers at various wavelengths in an attempt to examine the long wavelenght shift from calcified plaque stained with chlorotetracycline-hydrogen chloride. Fluorescence measurements were made at 351.9 nm cw UV excitation as well as 351, 308, and 248 nms pulsed excimer excitation. The typical native normal tissue fluoresced at ∼460 nm while plaque fluoresced at ∼475 nm. After staining the normal tissue had a peak maximum which red-shifted slightly while the calcified plaque now had a fluorescence maximum close to 540 nm, a very large red shift in the peak maximum. These results indicate that chlorotetracycline-hydrogen chloride clearly binds preferentially to calcified regions of aortic valves and arteries, and in doing so generates a long wavelength emission with any ultraviolet laser source, pulsed or cw. Thus, the long wavelength peak at 540 nm might be used to pinpoint calcific atherosclerotic lesions in cardiovascular tissue before removing it by laser ablation.     

1.1-W cw Cr:LiSAF laser pumped by a 1-cm diode array

We demonstrate 1.1-W cw output power from a diode-laser array-pumped Cr:LiSAF laser based on a concept that allows for pumping low-gain solid-state lasers at reduced temperature rise. We discuss scaling to higher powers as a function of diode power and define a figure of merit for evaluating given diode lasers as pump sources for low-gain solid-state lasers.     

A reliable cw Lyman-α laser source for future cooling of antihydrogen

We demonstrate a reliable continuous-wave (cw) laser source at the 1 S–2 P transition in (anti)hydrogen at 121.56 nm (Lyman-α) based on four-wave sum-frequency mixing in mercury. A two-photon resonance in the four-wave mixing scheme is essential for a powerful cw Lyman-α source and is well investigated.     

Continuous-wave wavelength conversion for high-power applications using an external cavity diamond Raman laser

We demonstrate continuous-wave (cw) operation of a diamond Raman laser at 1240 nm in an external cavity configuration. The output power increased linearly with pump power with a 49.7% slope efficiency and reached 10.1 W at the maximum available pump power of 31 W. The combination of resonator design with diamond provides a novel approach to power-scalable cw wavelength and beam conversion.     

Femtosecond laser pumped by high-brightness coherent polarization locked diodes

We demonstrate, for the first time to our knowledge, the use of a coherent polarization locked diode as the high-brightness pump source for a femtosecond laser. Four diode emitters are coherently locked to produce more than 5 W linearly polarized, narrow linewidth, and single-lobed pump beam. This gives >10× brightness improvement over the conventional diode array. The diode beam is then used to pump a Yb:KYW laser to obtain 2 W output with 57% slope efficiency in cw laser operation. By using a saturable absorber mirror, we achieved cw mode-locking operation with a 177 fs pulse width at an average power of 0.55 W.     

High-speed photonically assisted analog-to-digital conversion using a continuous wave multiwavelength source and phase modulation

A more simple photonically assisted analog-to-digital conversion system utilizing a cw multiwavelength source and phase modulation instead of a mode-locked laser is presented. The output of the cw multiwavelength source is launched into a dispersive device (such as a single-mode fiber). This fiber creates a pulse train, where the central wavelength of each pulse corresponds to a spectral line of the optical source. The pulses can then be either dispersed again to perform discrete wavelength time stretching or demultiplexed for continuous time analog-to-digital conversion. We experimentally demonstrate the operation of both time stretched and interleaved systems at 38 GHz. The potential of integrating this type of system on a monolithic chip is discussed.