Kilohertz pulse repetition frequency slab Ti:sapphire lasers with high average power (10 W)

High-average-power broadband 780-nm slab Ti:sapphire lasers, pumped by a kilohertz pulse repetition frequency copper vapor laser (CVL), were demonstrated. These lasers are designed for damage-free power scaling when pumped by CVL's configured for maximum output power (of order 100 W) but with poor beam quality (M(2) ~ 300). A simple Brewster-angled slab laser side pumped by a CVL produced 10-W average power (1.25-mJ pulses at 8 kHz) with 4.2-ns FWHM pulse duration at an absolute efficiency of 15% (68-W pump power). Thermal lensing in the Brewster slab laser resulted in multitransverse mode output, and pump absorption was limited to 72% by the maximum doping level for commercially available Ti:sapphire (0.25%). A slab laser with a multiply folded zigzag path was therefore designed and implemented that produced high-beam-quality (TEM(00)-mode) output when operated with cryogenic cooling and provided a longer absorption path for the pump. Excessive scattering of the Ti:sapphire beam at the crystal surfaces limited the efficiency of operation for the zigzag laser, but fluorescence diagnostic techniques, gain measurement, and modeling suggest that efficient power extraction (>15 W TEM(00), >23% efficiency) from this laser would be possible for crystals with an optical quality surface polish.     

Efficient Operation of an Intracavity-Doubled Nd:YVO(4)/KTP Laser End Pumped by a High-Brightness Laser Diode

Using a 1-W high-brightness laser diode as the pump source, we investigated the output characteristics of an intracavity frequency-doubled Nd:YVO(4)/KTP laser. Highly efficient operation was realized based on an optimized cavity design. The second-harmonic output power at 532 nm was measured to be 286.5 mW at an incident pump power of 881.4 mW, corresponding to an optical-to-optical efficiency of 32.5%.     

1053-nm-wavelength selection in a diode-laser-pumped Nd:YLF laser

We report on a Nd:YLF laser that operates at 1053 nm without optical intracavity elements for the suppression of the stronger 1047-nm transition. The Nd:YLF crystal is end pumped by a fiber optically coupled 10-W diode-laser bar. The different thermal-lensing focal lengths of the two main lasing wavelengths in a plane-parallel resonator were used to achieve the selection by tilting the end mirror slightly from its optimum position for maximum output power. With 9.8-W cw diode-laser-pumping power the 1053-nm Nd:YLF laser produces a maximum output power of 1.9 W in cw operation and nearly 1 W of average power at a Q-switch repetition rate of 15 kHz. The highest slope efficiency of 47% achieved in cw operation.     

Design and fabrication of a diode-side-pumped Nd:YAG laser with a diffusive optical cavity for 500-W output power

A ray-tracing code has been developed, and the design parameters of the laser pump head were analyzed in terms of crystal diameter, doping concentration, and optical cavity diameter. According to the numerical analysis, we fabricated an efficient diode-pumped Nd:YAG laser and experimentally obtained 500-W output power. The output power is close to the numerically calculated output power of approximately 450 W and corresponds to an optical-to-optical conversion efficiency of 46.7% and an optical slope efficiency of 49%.     

Low-threshold self-starting femtosecond Ti:sapphire laser

A low-threshold self-starting Kerr-lens mode-locked Ti:sapphire laser is demonstrated that uses a tight-focusing cavity design in conjunction with a semiconductor saturable-absorber mirror (SESAM). With 3% and 12% output couplers, we achieve mode-locking thresholds as low as 390 and 600 mW, respectively. Stable femtosecond laser pulses with average power of 114 mW are generated at a pump power of 1.2 W, which corresponds to a typical duration of 17 fs and bandwidth of 47 nm. Mode-locking operation is achieved in a pump power range of 600 mW to 4.8 W at an output coupling of 12%; the advantages of using a SESAM for low-power mode-locking operation are demonstrated.     

Unidirectional single-mode Nd:YAG laser with a planar semimonolithic ring cavity

Unidirectional single-mode operation of a diode-pumped Nd:YAG laser with a planar semimonolithic ring cavity has been demonstrated at 1064 nm. The semimonolithic cavity consists of a laser active medium placed in a magnetic field, a crystal quartz plate, and an output coupling mirror, which form an optical diode by acting as a Faraday rotator, a reciprocal polarization rotator, and a partial polarizer, respectively. A single-mode output power of 155 mW and a slope efficiency of 17% were obtained with a 1.2-W diode laser at 809 nm. A laser linewidth of less than 100 kHz is inferred from a beat note frequency spectrum between two identical laser systems and continuous tuning to greater than 2 GHz was observed.     

An all solid-state narrow bandwidth optical parametric oscillator and its applications to the high resolution spectroscopy of free radicals

The paper describes the design, performance and illustrative spectroscopic applications of a high power, pulsed, injection seeded, narrow bandwidth and continuously tuneable optical parametric oscillator (OPO) based on two β-barium borate (BBO) nonlinear crystals. A ring cavity OPO was injection seeded with an external cavity diode laser in the spectral range 755–855 nm. The OPO generated high power transform limited nanosecond light pulses in this range and, simultaneously, at 606–667 nm. Spectral parameters of the OPO were investigated as a function of pump power for two different cavity lengths. A bandwidth of ～120 MHz (0.004 cm^-1) in the visible has been achieved with a 40-cm-long cavity. The potential of the OPO system is demonstrated by recording high resolution sub-Doppler spectra in the UV of PF and C₃ radicals in a pulsed supersonic jet expansion.     

Frequency switching multiwavelength Brillouin Raman fibre laser based on feedback power adjustment technique

A simple switchable multiwavelength Brillouin–Raman fibre laser (BRFL) was demonstrated. The laser was arranged in a half-open cavity configuration including a physical mirror device with an adjustable reflectivity at one side of the laser cavity. The impact of the feedback power adjustment on frequency switching was carried out by comparing the peak power difference between odd- and even-order Stokes lines. Up to 468 flat-amplitude lines with a 10?GHz frequency spacing and average optical signal to noise ratio (OSNR) of 33 dB were observed with mirror reflectivity values of ～15% up to 60% at a 1534?nm Brillouin pump power of 7?dBm and 0.9?W Raman pump power of 0.9?W. – Under the same pumping conditions, setting the mirror reflectivity at its OFF state (where reflectivity is nearly 0%) allows for up to 242 lines with 20?GHz spacing to be realized, with ONSR values of ～35?dB.     

Tunable continuous-wave doubly resonant optical parametric oscillator by use of a semimonolithic KTP crystal

A temperature-tuned continuous-wave doubly resonant optical parametric oscillator (OPO) consisting of a semimonolithic KTP crystal and a concave mirror has been designed and built. Under single-axial-mode-pair operation, we obtained a combined output power of the signal and idler light fields up to 365 mW at a pump power of 680 mW. The output wavelength of the OPO can be temperature tuned by as much as 9 nm. We achieved 2.8-GHz continuous frequency tuning of the OPO by tuning the pump laser frequency.     

Efficient diffusive reflector-type diode side-pumped Nd:YAG rod laser with an optical slope efficiency of 55%

We fabricated a compact diode side-pumped Nd:YAG laser with a diffusive reflector, in which the diode laser power is transferred directly into the threefold symmetric diffusive cavity through long narrow slits. With a 7.5% output coupler in a linear resonator, we obtained 62.4-W multimode output power with an optical slope efficiency of 53.4% at a diode power of 182 W, which corresponds to an optical-to-optical efficiency of 34.3%. The optical slope efficiency increased to 55.5% when we used an 11% output coupler. From the leakage power analysis method, the pumping efficiency was measured to be approximately 82%. We discuss the thermal lens and the slope efficiency with respect to absorbed power that is derived from the measured pumping efficiency.     

Powerful and tunable operation of a 1-2-kHz repetition-rate gain-switched Cr:forsterite laser and its frequency doubling

We present a comprehensive study of the optimum operating regime in gain-switched Cr:forsterite lasers pumped at kilohertz repetition rates, comparing five crystals of similar quality but different dopant levels. The optimization of the cavity design includes selection of the proper pump fluence to account for excited-state absorption, optimum matching of the pump and laser modes, and consideration of thermal effects. As a result >1-W average output power is demonstrated at 2 kHz. The maximum conversion efficiencies achieved at 1 kHz are 24.2% (slope) and 20% (absolute). Narrow-band operation of this laser is possible with a birefringent filter, which is a prerequisite for efficient frequency doubling to cover the 585-660-nm part of the visible spectral range. Tunable second-harmonic generation in a temperature-tuned noncritical scheme that employs LiB(3)O(5) produces 60 mW of average power near 619 nm with 13.5% conversion efficiency.     

Compact and Efficient 3.2-W Diode-Pumped Nd:YVO(4)/KTP Green Laser

We demonstrate a simple way to achieve single-frequency operation by using fiber-coupled diode-pumped Nd:YVO(4)/KTP green lasers in a short standing-wave linear cavity. A single-mode output with 3.2-W green power was generated with a 12.6-W pump power corresponding to a conversion efficiency of 25.4%. The single-mode operation was obtained through the combined action of the anisotropic emission cross section of Nd:YVO(4) and the KTP crystal acting as a birefringent filter.     

International Intercomparison of Laser Power Measurements in the Visible Region

In this paper we describe results of the international intercomparison of He-Ne and Ar-ion laser power measurements. The intercomparison measurements were of He-Ne laser power of 3 mW at the wavelength of 633 nm and Ar-ion laser power of 200 mW at 488 nm and 515 nm. The participating laboratories coincided within deviation from the average of 0.6 percent at 633 nm, 0.8 percent at 488 nm, and 0.9 percent at 515 nm.     

High-power narrow-linewidth quasi-CW diode-pumped TEM00 1064 nm Nd:YAG ring laser

We demonstrated a high average power, narrow-linewidth, quasi-CW diode-pumped Nd:YAG 1064 nm laser with near-diffraction-limited beam quality. A symmetrical three-mirror ring cavity with unidirectional operation elements and an etalon was employed to realize the narrow-linewidth laser output. Two highly efficient laser modules and a 90° quartz rotator for birefringence compensation were used for the high output power. The maximum average output power of 62.5 W with the beam quality factor M(2) of 1.15 was achieved under a pump power of 216 W at a repetition rate of 500 Hz, corresponding to the optical-to-optical conversion efficiency of 28.9%. The linewidth of the laser at the maximum output power was measured to be less than 0.2 GHz.     

Three-longitudinal-mode He-Ne laser frequency stabilized at 633 nm by thermal phase locking of the secondary beat frequency

We present a simple scheme for thermal frequency stabilization of a three-longitudinal-mode He-Ne laser at 633 nm with improved short-term (5 x 10(-11) at 1-s average time) and long-term (124-kHz standard deviation for 10 h) frequency stability. A stabilized output power of 3 mW was readily obtained from the central mode by polarization-mode selection. The optical frequency of the central mode could be precisely tuned by an external frequency reference over 160 MHz with high precision or could be optically phase locked to a reference laser by use of a thermal frequency-stabilization circuit and an external acousto-optic modulator. The laser will be useful in various applications for which a laser source with high power and frequency stability is necessary.     

Results of International Comparisons Using Methane-Stabilized He-Ne Lasers at 3.39 ?m and Iodine-Stabilized He-Ne Lasers at 633 nm

The results of international comparisons of methane-stabilized He-Ne lasers at ? = 3.39 ?m and iodine-stabilized He-Ne lasers at 633 nm, made by beat frequency techniques, between Bureau International des Poids et Mesures (BIPM) and eleven national laboratories are presented. Generally, the measured frequency differences were inside ±4 × 10-11; but greater frequency differences were observed with some iodine cells (probably as a result of contamination) or when the output power of one laser was two or three times greater than the power of the other laser.     

Multiwavelength output from a Nd:YAG /Cr:LiSAF hybrid laser

A prototype solid-state, multispectral hybrid laser has been designed and tested. The laser provides simultaneous outputs at several wavelengths. The hybrid-laser concept is based on the efficient use of flash-lamp-pump energy distributed between two complementary lasing materials, Nd:YAG and Cr:LiSAF, that share the same pump cavity. The prototype Q-switched hybrid laser provides dual-fundamental-wavelength output at 850 and 1064 nm as well as frequency-doubled output at 532 nm. The laser achieved 3.6% slope efficiency (combined) in free-running operation and 2.4% when Q switched. Higher efficiencies can be obtained with improvements in laser crystal quality and pump cavity configuration.     

Two-photon Absorption and Nonlinear Optical Properties of A New Organic Dye DEASPI

A new organic dye trans-4- [p-(N,N-diethylamino) styryl]-N-methylpyridinium iodide (abbreviated' as DEASPI thereafter) with large two-photon absorption (TPA) cross section and excellent upconverted lasing properties was synthesized. The melting point and decompound point were measured to be 230 degreesC and 264.7 degreesC respectively. The molecular TPA cross section was measured to be sigma (2)=6.9x10(-48) cm(4).s/photon at 1064 nm by using an open aperture Z-scan system. The linear and nonlinear optical properties of this dye were systematically studied. The highest net upconversion efficiency from the absorbed pump energy to the output upconverted lasing energy is as high as 18.6% at the pump energy of 2.17 mJ from a mode-locked Nd:YAG ps laser. The nonlinear transmittance at the wavelengths from 720 to 1100 nm was measured. The dye solution also shows a clear optical power limiting effect.     

Efficient double-clad thulium-doped fiber laser with a ring cavity

We have constructed a novel ring cavity for a double-clad thulium-doped fiber laser, by placing the fiber's 45 degrees angle-polished output end before the input end and relaunching the pump and the laser power into the fiber. This design can reduce reabsorption by using short fibers without loss of pump efficiency. The dependence of the laser's performance on the fiber's length and the output coupler's reflectivity is investigated experimentally and theoretically. With an 80-cm-long fiber, 2.7-W single-mode continuous-wave output is generated for 11.5 W of launched pump power.     

Laser and Fluorescence Properties of Organic Dye DCM Doped Sol-Gel-Derived Solid-State Materials

1.IntroductionSol-gelprocessingoffersanewandeasyap-proachforproducingthermallysensitivedyedopedsolid-statematerialswithgreaterhomogeneityandhighconcentrationofdyemoleculesataroundroomtemperaturel1'2].Inthepastdecades,therehavebeenmanyreportsonsolid-statedyelasersbasedonpoly-merandsol-gelsl3~6l.Althoughencouragingprogresshasbeenachievedindyedoped1asersbasedonpoly-mermaterials,lowthermoconductivityandlaserdam-agethresholdarestillthemaindefectsofpolymerdyelasers.Recentadvancesinsol-gelOrmosilhav…