Amplified Spontaneous Emission Reduction by Use of Stimulated Brillouin Scattering: 2-ns Pulses from a Ti:Al(2)O(3) Amplifier chain

We constructed a cw Ti:Al(2)O(3) master oscillator-dye preamplifier-Ti:Al(2)O(3) power amplifier system that generates <2-ns, 100-mJ pulses. The system is tunable from 750 to 890 nm and has a repetition rate of 30 Hz. The output pulse has a near Fourier-transform-limited bandwidth of ~240 MHz. Backward stimulated Brillouin scattering is used to control the growth of amplified spontaneous emission (ASE). The content of ASE in the final output is under our detection limit (<10(-4)) for the entire tuning range.     

High-bandwidth laser-pulse generator using continuous-wave lasers

A laser-pulse generator for the transfer of continous-wave (cw) absolute radiometric calibrations to high-speed pulse photodetectors is described. The cw input lasers are modulated by a spinning polygon mirror in a ring cavity to produce high-speed, constant-amplitude, constant-shape laser pulses. Constantamplitude outputs range temporally from cw to 15-ns full-width at half-maximum (FWHM) Gaussian pulses. An all-reflective optical design permits operation of the device from the visible to the far-infrared spectral regions. Design and performance estimates for the pulse generator as well as experimental verification are presented.     

Pulse compression with a high-energy Nd:YAG regenerative amplifier system

We describe a method for the generation of readily synchronizable, near-transform-limited, 1064-nm, 6-mJ pulses with <20-ps duration at a repetition rate of 20 Hz. The method employs chirped pulse amplification of spectrally broadened and temporally stretched pulses from a cw mode-locked Nd:YAG laser in a commercial Nd:YAG regenerative amplifier followed by pulse compression with a grating pair. Linear amplification subsequent to regenerative amplification is not required with this method, although higher energies would be easily obtained.     

A Gigawatt High-Voltage Generator for Coherent Soft X-Ray Generation

A fast gigawatt high-voltage generator was developed to drive an argon-filled capillary for the generation of pulses of coherent short wavelength radiation in the extreme ultraviolet and soft X-ray region. A four-stage double Marx bank that is capable of delivering voltage pulses of 150 to 350 kV at 290-ns transition duration was used to pulse charge a 5-Omega-impedance water-filled pulse-forming line. A fast current pulse with amplitude ranging from 9 to 21 kA and 35-ns transition duration was generated through a 20-cm-long and 3-mm-diameter alumina channel filled with argon. Laser emissions in the Ne-like Ar at 46.9 nm have been observed in the pressure range of 0.14-0.38 mbar. It was also observed that over the spectral range from 20 to 70 nm, no other transitions, except the 46.9-nm line, experienced high gain and strong amplification.     

Duty cycle ratio dependence on the performance of a q-switched laser with an Er3+-Yb3+ codoped glass waveguide

We examine the performance of a hybrid Q-switched LiNbO(3) and Er(3+)-Yb(3+) doped glass waveguide laser as a modulation function of the duty cycle ratio. As the duty cycle ratio decreases, the laser operates at higher peak power and pulse width. At low duty cycle ratio (<1%), we observe variations in the Q-switched pulse shape; while the laser produces 59-W and 200-ns pulses to a 1-kHz repetition rate for a 50% duty cycle, it yields 27-W and 100-ns pulses to a 10-kHz repetition rate for a 0.01% duty cycle.     

High-energy,all-solid-state,ultraviolet laser power-amplifier module design and its output-energy scaling principle

We demonstrate that a coaxially pumped, large-aperture ultraviolet power-amplifier module with solid-state tunable laser medium Ce(3+):LiCaAlF6 has 98-mJ, 290-nm, and 3-ns output pulses with a sufficient extraction efficiency of 25%. The detailed information of design parameters, including the gain-coefficient dependence on pump condition, is successfully accumulated for further energy scaling for a terawatt-class ultraviolet chirped pulse amplification laser system or a high-pulse-energy laser system.     

Efficient Continuous-Wave and Q-Switched Operation of a 946-nm Nd:YAG Laser Pumped by an Injection-Locked Broad-Area Diode Laser

The efficient, low-threshold operation of a 946-nm Nd:YAG laser pumped by an injection-locked broad-area diode laser is reported. The implications of pump-beam quality for efficient, low-threshold operation, particularly with intrinsically inefficient transitions, are discussed in the context of previously published models. Results are presented showing that the M(2) = 1.3 pump beam of the injection-locked diode laser enabled a cw slope efficiency of 48% and a threshold of 52 mW to be attained. When Q-switched, 335 mW of pump power gave 27-ns, 5.2-muJ pulses. These were frequency doubled to obtain 19-ns, 1-muJ pulses at 473 nm. These results represent significant improvements over similar systems pumped by free-running broad-area diode lasers or arrays.     

Optical limiting studies in a carbon-black suspension for subnanosecond and subpicosecond laser pulses

This paper presents results of measurements of short (0.3 ps, 0.2 ns, and 10 ns) laser pulse transmissions through a liquid suspension of fine carbon particles (named CBS for "carbon-black suspension") at input-pulse energies up to 10 mJ. The 10-ns pulses came from a Nd:YAG laser at 1064 nm, and the shorter pulses came from a Ti:sapphire laser at 800 nm. Limiting was observed with the 10-ns and the 0.2-ns laser pulses, but the 0.3-ps pulses produced white light and underwent the same level of attenuation in the solvent and in the CBS.     

Injection-seeded pulsed alexandrite laser for differential absorption lidar application

We describe a Q-switched alexandrite laser injection seeded with a cw single-mode titanium-sapphire laser. The reported experimental results show that this system meets the frequency stabilization required for differential absorption lidar measurement of humidity, pressure, and temperature. The emission of the cw titanium-sapphire master oscillator is locked to an atmospheric absorption line by means of a servoloop with derivative spectroscopy. The spectral position is stabilized within ±3.5 × 10(-4) cm(-1) (10 MHz) of the peak of the line over 1 hr. The alexandrite laser emits pulses of 30 mJ in 500 ns, with a spectral linewidth of ≈ 3.3 × 10(-3) cm(-1) (100 MHz). The position of the centroid of the emitted spectrum has a standard deviation of 6 × 10(-4) cm(-1) (18 MHz) and is held within ±1.3 × 10(-3) cm(-1) (40 MHz) of the peak of the absorption line over 1 h.     

Wide-bandwidth adjustable Q switch based on rubidium dimers

A new type of Q switching for a flash-lamp-pumped Nd:YAG laser based on the saturable absorption of rudibium dimers is demonstrated. The variation of laser parameters such as output energy, pulse length, and repetition rate by means of temperature-controlled vapor pressure is shown. For a temperature of 320°C, a train of 40-ns pulses separated by 6-μs intervals is generated. When the temperature is 360°C, a single giant pulse with energy of 100 mJ and a pulse length of 10-15 ns is observed. Comparison with a solid-state passive Q switch based on LiF is provided. The new cell construction, consisting of a sealed-off sapphire cell containing rubidium vapor, is proposed for reliable, efficient, adjustable Q switchingthat is applicable to all types of solid-state lasers. The advantages of this mechanism of Q switching, such as thermal insensitivity, frequency locking and line narrowing, and wide spectral bandwidth, covering 0.6-1.3 μm, are discussed.     

High-power dye laser using steady-state amplification with chirped pulses

Steady-state chirped-pulse amplification was applied to a five-stage dye amplifier system to extract available energy over the full gain duration and at the same time suppress the amplified spontaneous emission (ASE). An output energy of 41 mJ was generated with 1.4-ns chirped pulses having an ASE of 3% and a pumping efficiency of 8.8% for the final amplifier. After five-stage amplification these pulses were compressed to 320 fs FWHM.     

Random laser action from a natural flexible biomembrane-based device

Abstract

Incoherent random lasing action in flexible eggshell membranes infiltrated with rhodamine 6G laser dyes is demonstrated. Laser radiation is achieved by exciting samples with 1-ns pulses at 526 nm. A threshold of 58 μJ/pulse is measured for the samples. The minimum threshold decreases to 35 μJ/pulse after the sample is coated with gold nanoparticles using a magnetron sputtering technique. The peaks of emission spectra are observed to redshift from 576 to 596 nm as dye concentration rises from 0.03 to 0.6 wt%. A linewidth of approximately 5 nm is obtained for most samples. This study is expected to offer a new way to induce lasing emission using biological microfibrils, and enriches basic knowledge of biophotonics.     

Broadly tunable femtosecond pulse generation in the near and mid-infrared

High-repetition-rate (80-MHz) femtosecond infrared pulses are generated by difference frequency mixing (DFM) a femtosecond Ti:sapphire laser with a phase-locked synchronized cw mode-locked Nd:YAG picosecond laser. This DFM scheme is of particular interest for generating ultrashort near-IR pulses (~10 fs) because group velocity mismatch with a pump pulse can be ignored. The simplicity and the broad wavelength tunability (from the near IR to the mid-IR) of this scheme is demonstrated. Short (125-fs FWHM) optical pulses in the near IR around 1.5 mum are obtained with noncritical type-I phase-matched LiB(3) O(5). We also used a similar scheme to generate mid-infrared pulses at 3.0 mum with type-II phase-matched KTiOPO(4).     

Linewidth-determining Processes in Distributed Feedback Dye Lasers

Abstract

Processes determining the linewidths of distributed feedback dye lasers (DFDL) have been investigated. Time resolution of the frequency of the output pulse shows that the linewidth, averaged over a pulse, arises predominantly from a dynamic sweeping of the laser frequency during the course of the pulse. This sweeping results from refractive-index changes in the dye over the duration of the pumping pulse; either through thermal effects or dispersion associated with the saturated gain. Thermal effects may be minimized by suitable choice of solvent but the dispersive sweep is inherent in this type of laser. The magnitude of the dispersive sweep changes across the tuning range of the laser. By judicious choice of dye solvent and dye parameters we have developed a narrow linewidth DFDL of 140 MHz for τ = 3·2 ns pulses, which is close to the transform limit.     

Picosecond-pulse wavelength conversion based on cascaded second-harmonic generation-difference frequency generation in a periodically poled lithium niobate waveguide

The wavelength conversion of picosecond optical pulses based on the cascaded second-harmonic generation-difference-frequency generation process in a MgO-doped periodically poled lithium niobate waveguide is studied both experimentally and theoretically. In the experiments, the picosecond pulses are generated from a 40 GHz mode-locked fiber laser and two tunable filters, with which the lasing wavelength can be tuned from 1530 to 1570 nm, and the pulse width can be tuned from 2 to 7 ps. New-frequency pulses, i.e., converted pulses, are generated when the picosecond pulse train and a cw wave interact in the waveguide. The conversion characteristics are systematically investigated when the pulsed and cw waves are alternatively taken as the pump at the quasi-phase-matching wavelength of the device. In particular, the conversion dependences on input pulse width, average power, and pump wavelength are examined quantitatively. Based on the temporal and spectral characteristics of wavelength conversion, a comprehensive analysis on conversion efficiency is presented. The simulation results are in good agreement with the measured data.     

Operation of a Ti:sapphire laser pumped by a 499-nm green laser

We report, for the first time, to our knowledge, the operation of a tunable Ti:sapphire laser pumped by a third-order Raman XeCl-H(2) laser system at 499 nm with a 60-ns pulse duration. The slope efficiency is 59% for this laser, producing pulses of 20-ns duration. The highest conversion-energy efficiency obtained is 41%, with an output energy of 1.2 mJ. The tuning range for a single set of cavity mirrors is 680-834 nm and is limited mainly by the mirror reflectivity. This study shows that a combined laser system based on a XeCl excimer laser can offer wavelength diversity.     

A simultaneous hit finding and timing method for pulse shape analysis of drift chamber signals

An algorithm for the analysis of the digitized signal waveform of drift chamber pulses is described which yields a good multihit resolution and an accurate drift time determination with little processing time. The method has been tested and evaluated with measured pulse shapes from the full size prototype of the OPAL central detector which were digitized by 100 MHz FADCs.     

Microchip lasers

Microchip lasers are miniature diode-pumped solid-state devices formed by dielectrically coating thin platelets of gain media. Their simplicity and small size give them the potential for inexpensive mass production, while their cw output characteristics are comparable to those of the best conventional devices. By incorporating a thin platelet of a second material into the device, tunable cw lasers and picosecond Q-switched microchip lasers have been produced which outperform larger devices in many aspects. Electrooptically tuned devices have demonstrated a flat-band tuning response of 15 MHz/V at modulation rates from dc to 1.3 GHz. Pulses as short as 115 ps, with peak powers of 80 kW, have been generated by electrooptically Q-switched microchip lasers, and pulse repetition rates as high as 2.25 MHz have been demonstrated. Passively Q-switched devices generate pulses as short as 218 ps and produce peak powers in excess of 130 kW, without the need for switching electronics. A variety of miniature nonlinear optical devices, including harmonic generators, parametric amplifiers, parametric oscillators, and fiber-based Raman amplifiers, have been used to frequency convert the output of these lasers, accessing the entire spectrum from 5 μm to 190 nm in extremely compact optical systems.     

Long-pulse narrow-linewidth dispersive solid-state dye-laser oscillator

We report on narrow-linewidth long-pulse laser emission from a dispersive solid-state dye-laser oscillator. Output energy was ~0.4 mJ/pulse at laser linewidths of 650 MHz and pulse lengths of 105 ns FWHM. The solid-state gain medium utilized was Rhodamine 6G dye-doped 2-hydroxyethyl methacrylate:methyl methacrylate.     

Optical limiting, pulse reshaping, and stabilization with a nonlinear absorptive fiber system

Optical limiting, pulse reshaping, and stabilization effects have been demonstrated based on a two-photon absorption mechanism with a dye-solution-filled hollow fiber system. The nonlinear absorptive medium is the solution of a new dye, trans-4-[p-(N-hydroxyethyl-N-methylamino)styryl]-N-methylpyridinium iodide (ASPI) in dimethyl sulfoxide, with which we filled a 20-cm-long quartz hollow fiber of 100-mum internal diameter. The input optical signal was a laser pulse train that contained ~30 pulses of 130-ps pulse width. When the input peak intensity reached 400-1000-MW/cm(2) levels, obvious optical limiting could be observed and the envelope of the transmitted pulse train became flatter and broader. By using another new dye solution, 4-[N-(2-hydroxyethyl)-N-(methyl)amino phenyl]-4?-(6-hydroxyhexyl sulfonyl)-stilbene (APSS) in benzyl alcohol, which interacted with a series of ~800-nm laser pulses of ~8-ns pulse width, we obtained a much higher nonlinear absorption coefficient and a superior optical peak-power stabilization effect.