Toward passive mode locking by nonlinear polarization evolution in a cascaded Raman fiber ring laser

We demonstrate a cascaded Raman fiber ring laser delivering a pulsed fourth-order Stokes component. Periodic emission of subnanosecond pulses is achieved from the interplay between nonlinear polarization evolution and Raman cascade process.     

High Efficient C6H12 Raman Laser Enhanced by DCM Fluorescence

We report the first-order Stokes output （wavelength of 627.6 nm） from C6H12 enhanced by DCM dye fluorescence with high energy conversion efficiency of 47.9%, quantum conversion efficiency of 56.5%. To our knowledge, it is the highest conversion efficiency of stimulated Raman scattering obtained from liquid Raman laser. A 532nm frequency doubled Nd：YAG laser with 8 Hz repetition rate is employed as the pump source, and the enhancement medium is DCM dye solution in ethanol. The conversion efficiencies at various pump energies and various pump repetition rates are measured and analysed. The enhancement mechanism of SRS together with its potential application is discussed.     

CW injection phase locking in homogeneously broadened media II. Phase locking and tunability of CO2 waveguide lasers

Injection phase locking of a powerful CO₂ waveguide laser with a stable singlefrequency master oscillator is described. The locking range is experimentally investigated versus both injected signal frequency and slave cavity length. A locking tunability up to ±180 MHz from CO₂ 10P(20) line center has been achieved. Experimental results are in excellent agreement with the theoretical development exposed in the preceeding paper.     

WG-Like Modes Selectivity in a Square Cavity with Posts

We investigate the characteristics of Whispering-Gallery（WG）-like modes in a square cavity with posts by employing the two-dimensional （2D） finite-difference time-domain （FDTD） technique combined with the effective index method. The results indicate that the posts can result in mode selection in the WG-like modes. The WG-like modes with odd mode numbers are not much sensitive to the sizes of the posts. However, the quality factor （i.e. Q-factor） of the WG-like modes with even mode numbers decreases sharply with the increasing size of the posts. The decreasing Q-factor is attributed to mode leakage and scattering loss due to the presence of the post. The mode selection increases the mode spacing of square cavity twice in an optimized structure.     

20-Hz operation of an eye-safe cascade Raman laser with a Ba(NO3)2 crystal

Operation of a 1.598-μm eye-safe third-Stokes Raman laser with a Ba(NO₃)₂ crystal pumped by a 1.064-μm Nd:YAG laser is described. We observed a substantial decrease in the output energy during the first 50 s of the continuous operation at 20 Hz. The energy drop is ∼76% of the initial third-Stokes output. We confirmed negative thermal lensing and thermally induced birefringence in the crystal. With a concave cavity mirror at a matched curvature to the thermal lensing, we obtained an output energy of 11 mJ at 20 Hz. TEM₀₀ output was also obtained with a smaller pump-beam diameter with a highest conversion efficiency of 15.5% for a pumping power of only 45 MW/cm² (0.9 J/cm²). Received: 20 November 2001 / Revised version: 20 February 2002 / Published online: 2 May 2002     

Spectral properties of diode-pumped non-planar monolithic Nd:YAG ring lasers

The coherence length of a single-frequency monolithic Nd:YAG ring laser is determined by using a highly unbalanced all-fiber Mach-Zehnder interferometer. A coherence length larger than 1500km and a 3 dB linewidth less than 60 Hz is estimated.Furthermore, an easy method to measure the temperature dependence on several laser parameters is described. This method is based on the laser emission in multiple axial modes, which is enforced by coherent optical feedback. A model explaining the multimode behaviour is presented.     

High-brightness ultraviolet excimer lasers

At present the performance of short-pulse rare-gas-halide excimer-laser systems is definitely below that of solid-state systems, as far as the maximum peak-power is concerned. However, short-pulse excimer lasers are expected to be the best candidates to produce the highest focused intensities (I 10²⁰ W/cm²) provided by the shorter wavelength and less optical distortion in the gaseous active medium. This is especially feasible if the present performance of short-wavelength focusing optics is improved, and the problem of the limited extraction efficiency of excimers is solved. In this paper the results of former developments, novel methods, such as spatially-evolving chirped-pulse amplification, off-axis amplification, interferometric multiplexing, and some considerations for the achievable maximum brightness of table-top excimer systems are presented.     

CW and quasi-CW diode-laser-pumped Nd:SSGM

Fiber-coupled laser diodes were used to pump a Nd-doped SGGM slab (Nd: 4at.%) in the Continous Wave (CW) and Quasi-CW (Q-CW) modes of operation. The optical-to-optical and slope efficiencies were determined in both cases.     

Diode End-Pumped Passively Q-Switched Nd^3＋：GdVO4 Self-Raman Laser at 1176 nm

A compact diode-end-pumped passively Q-switched Nd^3＋ ：GdVO4/C^r4＋ ：YAG self-Raman laser at 1176 nm is demonstrated. When the To = 80% Cr^4＋：YAG saturable absorber is inserted into the cavity, the maximum Rtaman laser output reaches 175 mW with 3.8 W incident pump power. The optical conversion from incident to the Raman laser is 4.6% and the slope efficiency is 6.5%. The pulse energy, duration, and repetition frequency of the first stokes laser are 4.5μJ, 1.8 ns, and 38.5 kHz, respectively. There is strong blue emission （about 350- 400nm） can be observed in the Nd^3＋ ：GdVO4 crystal when the process of stimulated Raman scattering occurs, which is induced by the upconversion of the Nd^3＋ ions.     

Compact, Low Threshold Nd^3＋：YVO4 Self-Raman Laser at 1178 nm

A compact low-threshold Raman laser at 1178 nm is experimentally realized by using a diode-end-pumped actively Q-switched Nd^3＋ ：YVO4 self-Raman laser. The threshold is 370mW at a pulse repetition frequency of S kHz. The maximum Raman laser output is 182 m W with the pulse duration smaller than 20 ns at a pulse repetition frequency of 30kHz with 1.8 W incident power. The optical efficiency from the incident power to the Raman laser is 10% and the slope efficiency is 13.5%.     

Diode laser coupled to a high-<Emphasis Type="Bold">Q</Emphasis> microcavity via a GRIN lens

A miniature high-coherent diode laser was developed. Optical feedback from a high-Q microsphere resonator was used to narrow the spectrum of the laser, and a nearly half-pitch gradient-index lens served as a coupling element. As estimated from the variation in frequency-tuning range (chirp-reduction factor) the fast line width of the laser was reduced by more than three orders. It is remarkable that the system reveals stable single-mode operation at a relatively high feedback level. A tentative explanation is presented in terms of previously given models. Received: 8 July 2002 / Revised version: 9 March 2003 / Published online: 24 April 2003 RID="*" ID="*"Corresponding author. Fax: +7-095/334-0249, E-mail: vvv@okb.lpi.troitsk.ru     

Nd:YAG split-disk laser amplifier for 10 J output energy

A prototype split-disk amplifier consisted of four Nd:YAG ceramics and single crystals was demonstrated with a 3.7 cm square clear aperture. A single-pass small-signal gain of 2.0 and a total stored energy of 11.1 J in the eight YAG disks were obtained. The maximum output energy of 10.4 J with the YAG disk amplifier was achieved in a single-shot operation. A near-field pattern of 31 mm × 31 mm square with super Gaussian shape was measured.     

Compact resonator designs for mode-locked solid-state lasers

Received: 16 February 1997/Revised version: 24 April 1997     

Noise as reliability screening for semiconductor lasers

The low-frequency electrical noise in semiconductor lasers is measured and used for device-reliability screening, which is a sensitive and non-destructive method. In the experiment, we developed some approaches to improve the validity of reliability screening by using noise criteria. A new method of determining the threshold level of noise criteria is given. The experimental results show that this method is effective. Received: 26 September 2002 / Revised version: 28 January 2003 / Published online: 9 April 2003 RID="*" ID="*"Corresponding author. Fax: +86-431/462-7013, E-mail: huguijun@sina.com     

Dynamics of lasers with two-dimensional distributed feedback

A model of a laser exploiting two-dimensional (2D) distributed feedback is developed. A new feedback mechanism can be realized using a dielectric structure with the width having double-periodical sinusoidal or chessboard modulation. It is shown that 2D Bragg resonator possesses high selectivity over both the longitudinal and the transverse indices. Within semi-classical approach nonlinear dynamics of 2D distributed feedback laser (DFL) is studied and spatial synchronization of radiation from extended active medium is demonstrated.     

Line-dependent saturation in CO2 lasers

Line dependent saturation has been studied in a CO₂ waveguide laser, operating cw in 100 lines of the 9 m and 10 m bands. In both bands, for constant discharge conditions, the saturation intensity is found to be strictly inversely proportional to the small signal gain for lines in the range J=2 to J=48 in both the P and the R branches. For lasers operating well above threshold this implies an output power which is essentially independent of the line number. The effect is verified experimentally, and discussed theoretically.Supported by the Danish Science Research Council under grant no. 11-7777     

Quasi-self-imaging planar waveguide lasers with high-power single-mode output

We describe high-power planar waveguide laser which can achieve single-mode output from a multi-mode structure. The planar waveguide is constructed with incomplete self-imaging properties, by which the coupling loss of each guided mode can be discriminated. Thermal lens effects are evaluated for single-mode operation of such high-power diode-pumped solid-state lasers.     

Sub-nanosecond microchip laser with intracavity Raman conversion

Efficient sub-nanosecond pulse operation of microchip lasers with intracavity Raman conversion and pulse compression is presented for the first time. The microchip lasers were composed of Nd:LSB or Nd:YAG laser crystals, Cr⁴⁺:YAG saturable absorber, and Ba(NO₃)₂ Raman medium. The pulse duration obtained at the Stokes wavelength (1196 nm) was as short as 118 ps. Optical conversion efficiency of laser-diode pump power to the Stokes power of 8% was reached. Pulse energy and peak power of Stokes emission were 1.2 μJ and 5.4 kW, correspondingly. Numerical calculations are in good agreement with obtained experimental results. Received: 20 December 2002 / Revised version: 6 March 2003 / Published online: 5 May 2003 RID="*" ID="*"Corresponding author. Fax: +1-716/645-6945, E-mail: ankuzmin@acsu.buffalo.edu RID="**" ID="**"Present address: University at Buffalo, SUNY, The Institute for Lasers, Photonics, and Biophotonics, 458 NSC, Buffalo, NY 14 260-3000, USA     

CW diode pumping and FM mode locking of a Nd: KGW laser

We have demonstrated cw diode end pumping of Nd: KGW, a novel solid-state gain medium, with up to 30% conversion efficiency into near-TEM₀₀ (M² < 1.05) output at = 1.067 µm for a pump level of 2.7 W. The slope efficiency was limited by intracavity reflections to 36%; however, direct comparison to a similar Nd:YAG laser indicates the same intrinsic slope efficiency of 60%. FM mode locking of this laser at 200 MHz has produced 12 ps pulses (compared to 16 ps for Nd: YAG), although an intracavity etalon was required. Considerable reduction in pulse width is possible (the line width limit is 0.5 ps) but different techniques may be necessary. Spatial hole burning was evident in both the 120 GHz free-running spectrum and the etalon-limited mode-locked spectrum.