Widely tunable continuous-wave Raman laser in diatomic hydrogen pumped by an external-cavity diode laser

What is to the authors' knowledge the first experimental demonstration of a nonresonant cw Raman laser pumped by a tunable external-cavity diode laser (ECDL) is presented. The ECDL is phase-frequency locked to a high-finesse Raman laser cavity containing diatomic hydrogen (H(2)) by the Pound-Drever-Hall locking technique. The Stokes lasing threshold occurs at a pump power of 400 +/- 30 muW, and a maximum photon conversion efficiency of 12.0 +/- 1.3% is achieved at 1.6 mW of pump power. A 40-nm tuning range of the cw Stokes emission, 1174-1214 nm, is obtained by tuning of the wavelength of the ECDL pump source.     

Continuous-wave rotational Raman laser in H(2)

A diode-pumped, far-off-resonance cw Raman laser in H(2) with rotational Stokes emission is reported for the first time to our knowledge. The Raman laser can produce single-wavelength emission at either 830 nm (rotational Stokes) or 1180 nm (vibrational Stokes) depending on the frequency tuning of the pump laser. The mirrors for the rotational cw Raman laser are easier to produce; the laser also exhibits a wider continuous tuning range and is less sensitive to thermal effects than the previously studied vibrational Raman laser [Opt. Lett. 26, 426 (2001) and references therein].     

High-conversion-efficiency, diode-pumped continuous-wave Raman laser

We demonstrate a diode-pumped cw Raman laser in H(2) with photon-conversion efficiency of (66+/-8)%. Pumped by an injection-locked diode laser at 792 nm, the Stokes laser produces a peak output power of ~16mW at 1180 nm. Accompanying the high Stokes power are deviations from the existing theory, which are believed to be caused by the thermal-lensing effect of the Raman gas.     

Three-cascaded 1407-nm Raman laser based on phosphorus-doped silica fiber

We report a laser-diode-pumped 1407-nm Raman fiber laser with an output power of 1 W. In this three-cascaded cw Raman laser, based on a single active phosphorus-doped silica fiber, for the first time to the authors' knowledge successive generation of Stokes components of essentially different frequency shifts (1330 and 490cm(-1)) has been realized. These Stokes components are associated with both constituents (P(2)O(5) and SiO(2)) of the fiber core glass.     

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.     

Subwatt threshold cw Raman fiber-gas laser based on H2-filled hollow-core photonic crystal fiber

We report on what is, to our knowledge, the first cw pumped Raman fiber-gas laser based on a hollow-core photonic crystal fiber filled with hydrogen. The high efficiency of the gas-laser interaction inside the fiber allows operation in a single-pass configuration. The transmitted spectrum exhibits 99.99% of the output light at the Stokes wavelength and a pump power threshold as low as 2.25 W. The study of the Stokes emission evolution with pressure shows that highly efficient Raman amplification is still possible even at atmospheric pressure. The addition of fiber Bragg gratings to the system, creating a cavity at the Stokes wavelength, reduces the Raman threshold power below 600 mW.     

High Power Photonic Crystal Fibre Raman Laser

A cw Raman laser based on a 100-m photonic crystal fibre is demonstrated with up to 3.8 W output power at the incident pump power of 12 W, corresponding to an optical-to-optical efficiency of about 31.6%.. The second order Stokes light, which is firstly reported in a cw photonic crystal fibre Raman laser, is obtained at 1183nm with an output power of 1.6 W and a slope efficiency of about 45.7%.     

Continuous-wave Raman laser pumped within a semiconductor disk laser cavity

A KGd(WO?)? Raman laser was pumped within the cavity of a cw diode-pumped InGaAs semiconductor disk laser (SDL). The Raman laser threshold was reached for 5.6 W of absorbed diode pump power, and output power up to 0.8 W at 1143 nm, with optical conversion efficiency of 7.5% with respect to the absorbed diode pump power, was demonstrated. Tuning the SDL resulted in tuning of the Raman laser output between 1133 and 1157 nm.     

Passively Q-switched fiber laser that uses saturable Raman gain

Operation of a short all-fiber passively Q-switched Raman laser pumped by a continuous-wave laser diode is experimentally demonstrated. The passively switched fiber laser consists simply of a double-clad ytterbium-doped silica fiber that is spliced directly to a moderately germanium-doped silica fiber. The placement of the Ge-doped silica fiber within the fundamental (Raman pump) cavity allows interplay between fundamental and Stokes fields to take place, which leads to saturation of the Raman gain as a result of pump depletion. Pulse widths of 70 and 60 ns at the first and second Stokes wavelengths of 1168 and 1232 nm, respectively, are produced at a stable 588 kHz repetition rate.     

Demonstration of long-term reliability of a 266-nm, continuous-wave, frequency-quadrupled solid-state laser using beta-BaB(2)O(4)

We report what we believe to be the first operation of more than 1000 h of a 266-nm (cw) frequency-quadrupled solid-state laser with a 100-mW output. We used beta-BaB(2)O(4)(BBO) crystal grown by the Czochralski method to double the green-light (532-nm) wavelength, using an external resonant cavity. The green light was generated with an intracavity frequency-doubled Nd:YVO(4)laser pumped by a 4-W laser diode. When the incident 532-nm power on the external resonant doubler was 500 mW, we generated 100 mW of cw 266-nm radiation with the BBO crystal. The degradation rate seems to be proportional to the strength of the UV optical electric field. We also obtained a relative intensity noise of -130dB/Hz at frequencies of 2 to 10 MHz for 266-nm laser light.     

Generation of a high-temporal contrast ultrafast laser pulse near 1,053 nm through stimulated Raman frequency shift

A high-temporal contrast femtosecond Stokes pulse near 1,053 nm is obtained simply without polarizer extinction ratio limitation based on the stimulated Raman frequency shift process in ethanol with an 800-nm femtosecond Ti:sapphire laser as a pump source. By optimizing the incident pump pulse chirp and the ethanol Raman cell length, a clean Stokes pulse near 1,053 nm with a maximum energy of 0.24 mJ is obtained with ~7.5 % conversion efficiency and 0.8 % (rms) energy fluctuation. Compared with the incident pump pulse, the temporal contrast of the Stokes pulse is improved by at least approximately three orders of magnitude.     

Diode-pumped singly resonant continuous-wave optical parametric oscillator with wide continuous tuning of the near-infrared idler wave

We demonstrate wide, continuous tuning of the single-frequency idler wave of a cw singly resonant optical parametric oscillator (SRO). The SRO consists of a periodically poled LiNbO(3) crystal for quasi-phase matching in a four-mirror signal-resonant ring cavity. The SRO, excited by 2.25 W of 924-nm radiation from an InGaAs diode laser, generates as much as 200 mW of single-frequency 2.1-mum idler radiation. We tune the idler frequency continuously within a range as large as 56 GHz by changing the wavelength of the diode pump laser. The versatility of this continuously tunable single-frequency infrared source is demonstrated by recording of N(2)O rovibrational absorption lines near 2.1 mum.     

Diode pumping of a continuous-wave Pr3+-doped LiYF4 laser

We report, for the first time to our knowledge, diode-pumped cw laser oscillation of Pr3+:LiYF4 in the red spectral range. The pump power is provided by a GaN laser diode emitting a maximum output power of 25 mW at a wavelength of approximately 442 nm. The Pr3+ laser emits 1.8 mW of output power at a 639.7-nm wavelength. Threshold pump power and slope efficiency in a nonoptimized setup are determined to be 5.5 mW and 24%, respectively.     

Multiwavelength L-band fiber laser with bismuth-oxide EDF and photonic crystal fiber

A multiwavelength laser comb using a bismuth-based erbium-doped fiber and 50 m photonic crystal fiber is demonstrated in a ring cavity configuration. The fiber laser is solely pumped by a single 1455 nm Raman pump laser to exploit its higher power delivery compared to that of a single-mode laser diode pump. At 264 mW Raman pump power and 1 mW Brillouin pump power, 38 output channels in the L-band have been realized with an optical signal-to-noise ratio above 15 dB and a Stokes line spacing of 0.08 nm. The laser exhibits a tuning range of 12 nm and produces stable Stokes lines across the tuning range between Brillouin pump wavelengths of 1603 nm and 1615 nm.     

The first-stokes pulse generation in Nd:KGW intracavity driven by a diode-pumped passively Q-switched Nd:YAG/Cr<Superscript>4+</Superscript>:YAG laser

The operation of an all solid-state pulsed Nd:KGW Raman laser pumped by compact passively Q-switched Nd:YAG/Cr:YAG laser is demonstrated. The first-Stokes radiation of stimulated Nd:KGW Raman scattering at the 1178 nm is generated. The average output power of 336 mW at Stokes wavelength was obtained under the laser diode pump power of 5.74 W. The corresponding optical efficiency from the diode light to the Raman output is 9.85%. The pulse width of 1.65 ns and a pulse repetition rate of 10 kHz were also obtained.     

输出功率稳定的二级喇曼光纤激光器特性

提出一种输出功率稳定的二级喇曼光纤激光器,从理论分析角度探讨了它的特性.结果表明：由于在抽运光的二级斯托克斯光频附近的自发辐射光的钳制作用,激光器的一级和二级输出功率几乎都不受抽运功率波动的影响,从而降低了抽运光低频相对强度噪音转移|激光器输出的一级和二级斯托克斯光功率都很稳定,并且通过调节激光器结构中的可变衰减器,可以有效控制一级、二级激光的输出功率以及它们的比值.这些特性表明该喇曼光纤激光器很适合于作为喇曼光纤放大器的抽运源.     

Efficient cw sodium dimer Raman laser operation in a high-temperature sapphire cell

cw Raman lasing of Na₂ molecules generated in a heated, sealed-off, all-sapphire cell is demonstrated. Being not damaged by highly corrosive alkaline vapours, this type of cell enables operation without buffer gas in contrast to the normal heatpipe operation of these lasers. This allows us to study Raman lasers in alkaline vapours in new regimes and under ideal conditions. With an argon ion pump laser at 488 nm, Raman laser operation at 525 nm with more than 10% efficiency and thresholds below 0.2 mW for a cell without buffer gas (length 9 cm) have been obtained so far. The low thresholds, being a factor of 10 less than for comparable heatpipe operation, gives us the chance to use low-power diode lasers as pump sources and to realize compact reliable Raman laser systems. Received: 17 May 1999 / Published online: 25 August 1999     

High-efficiency 1040 and 1078 nm laser emission of a Yb:Y2O3 ceramic laser with 976 nm diode pumping

We report a high-efficiency diode-end-pumped polycrystalline Yb:Y2O3 ceramic laser. Pumped by a 976 nm laser diode bar and with an absorbed pump power of 2.8 W, cw output power of 1.74 W at 1078 nm, and 0.73 W at 1040 nm were obtained. The slope efficiency was measured to be 82.4% for the 1078 nm laser emission and 57.1% for the 1040 nm laser emission.     

Combined Raman and continuous-wave-excited two-photon fluorescence cell imaging

We demonstrate a confocal optical microscope that combines cw two-photon-excited fluorescence microscopy with confocal Raman microscopy. With this microscope fast image acquisition with fluorescence imaging can be used to select areas of interest for subsequent chemical analysis with spontaneous Raman imaging. The distribution of the UV-absorbing fluorophore Hoechst 33342 in the apoptotic HeLa cells is measured in the combined cw two-photon-excited fluorescence and Raman microscopy modes. The 647-nm line of a Kr-ion laser is used to excite both the Raman scattering and the two-photon-excited fluorescence emission. The lateral and axial resolutions in the two imaging modes are compared by use of the Gaussian beam approximation and backprojection of the focal volume through the confocal pinhole.     

Coherent anti-Stokes Raman scattering and normal anti-Stokes Raman scattering due to LO phonons in GaP using cw diode lasers

Coherent anti-Stokes Raman scattering (CARS) and normal anti-Stokes Raman scattering (NARS) have been measured in (001) GaP at room temperature due to the 403 cm⁻¹ LO phonons using a continuous wave (CW) 785.0 nm fixed-wavelength pump laser and a CW Stokes laser tunable in the 800-830 nm wavelength range. CARS measurements are normally made using pulsed lasers. The use of CW diode lasers allows a more accurate comparison between the measured and calculated values of the CARS signal. The pump and Stokes laser beams were linearly polarized perpendicular to each other, same as the pump and normal Stokes/anti-Stokes scattered light for the GaP sample used in this work. The pump and Stokes laser powers incident upon the GaP sample, located in the focal plane of a 20 mm effective focal length lens, were <20 and 50 mW, respectively. The diameter of the laser beams in the focal plane of the focusing lens was determined to 40±5 μm. The pump and Stokes laser beam intensities incident upon the 0.3 mm thick GaP sample were <2 and 5 kW cm², respectively. The powers of the CARS and NARS signals were measured using a Raman spectrometer. The signal output of the Raman spectrometer was calibrated using the pump laser and several neutral density filters. The Raman linewidth (full-width at half-maximum) of the LO phonons was determined to be 0.95±0.05 cm⁻¹, using the variation of the CARS signal with the wavelength of the Stokes laser. The measured powers of the CARS and NARS signals are about a factor of 5 and 1.5, respectively, smaller than those calculated from the corresponding theoretical expressions.