Highly efficient, widely tunable, 10-Hz parametric amplifier pumped by frequency-doubled femtosecond Ti:sapphire laser pulses

We report a 10-Hz, highly efficient, widely tunable (from the visible to the IR), broadband femtosecond optical parametric generator and optical parametric amplifier (OPA) in BBO, LBO, and CBO crystals pumped by the frequency-doubled output of a regeneratively amplified Ti:sapphire laser at 400 nm. The output of the system is continuously tunable from 440 nm to 2.5 mum with a maximum overall efficiency of ~25% at 670 nm and an optical conversion efficiency of more than 36% in the OPA stage. The effects of the seed beam energy, the type of the crystal and the crystal length, and the pumping energy of the output of the OPA, such as the optical efficiency, the bandwidth, the pulse duration, and the group velocity mismatch between the signal and the idler and between the seeder and the pump, are investigated. The results provide useful information for optimization of the design of the system.     

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.     

Regenerative amplification of femtosecond pulses at 745 nm in Ti:sapphire

A regenerative amplifier for femtosecond pulses that operates at a wavelength off the peak gain of Ti:sapphire is reported. Apair of prisms and an adjustable slit are used in the intracavity space so that the operating wavelength can be tuned to 745 nm. The amplified and compressed pulse is 92 fs (Gaussian profile assumed) at an energy of 1 mJ. The pumping efficiency is 12.5%.     

Growth of Ti:sapphire single crystal thin films by pulsed laser deposition

This paper documents the growth of single crystal Ti:sapphire thin films, typically 10 μm thick, on undoped sapphire substrates using pulsed laser deposition from a Ti:sapphire single crystal target with a doping level of 0.1 wt.% Ti₂O₃. These thin films are shown to have very high crystal quality using ion beam channelling and X-ray diffraction techniques. The degree of titanium incorporation into the films is investigated using inductively coupled plasma mass spectrometry and particle induced X-ray emission. These techniques show that levels of up to 0.08 wt.% Ti₂O₃ are present in the deposited layers.     

High-energy picosecond near-vacuum ultraviolet pulses generated by sum-frequency mixing of an amplified Ti:sapphire laser

We demonstrate high-energy picosecond near-vacuum ultraviolet laser pulse generation. Frequency quadrupling is achieved by noncollinear sum-frequency mixing of the fundamental and the third harmonic of a two-stage Ti:sapphire amplifier in beta-BaB(2)O(4) crystal. UV pulses with energies of approximately 10 mJ tunable from 195 to 210 nm at a 10 Hz repetition rate are obtained.     

Surface polish characterization of industrial Ti: sapphire laser crystal rods by photopyroelectric scanning imaging

Photopyroelectric scanning imaging of a Ti:sapphire crystal with three different surface polishes was carried out using a novel non-contact experimental configuration. Bulk optical absorption coefficient, surface optical absorptance and theoretically normalized quadrature (Q) signal images were obtained. In addition to growth defects in the crystal, the photothermal Q images revealed variations due to the quality of surface polishes in terms of surface optical absorptance, and thermal resistance and homogeneity of each polish. Purely optical-transmission scanned images exhibited lower sensitivity to the degree of the defective state of the Ti:sapphire rod surface due to polishing. It is concluded that photopyroelectric scanning imaging can be used in the quality control of both crystal growth and surface processing of Ti:sapphire crystals.     

Comparative study of generation characteristics of CdS crystal laser pumped by low- and high-energy electron beams

A CdS crystal has been excited by radially converging pulsed electron beam with an electron energy of up to E ≈ 18 keV, a beam current density at the target of up to 4 kA/cm², and a pulse full width at half maximum within τ ≈ 12–100 ns. For comparison, the same crystal was pumped by electrons with E = 170 keV at τ = 2.2 ns. A specific distinctive feature of the excitation by powerful low- and high-voltage electron beams is the appearance of previously unreported long-wavelength generation with a peak at λ ≈ 535 nm in the electron-hole plasma band. In the region of the interband transition with a peak at λ ≈ 515 nm, the generation spectra are similar to those known from the literature.     

Generation of Fourier-transform-limited 35-ns pulses with a ramp-hold-fire seeding technique in a Ti:sapphire laser

We report on an injection-seeded Ti:sapphire laser pumped by the second harmonic of a Nd:YAG laser. The resonance between the low-power seed laser and the slave cavity is achieved by a ramp-hold-fire technique. Because of the triangular cavity design, the spatial beam profile is excellent; and combined with the narrow-linewidth pulses, the conversion efficiencies for nonlinear frequency generation are excellent.     

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.     

Direct Bonding of Ti:sapphire laser Crystals

Direct bonding without the use of adhesive materials was demonstrated on a titanium-doped sapphire laser crystal with a bonding surface dimension of 12 mm x 6 mm(2). The bonding surfaces were treated with chemical processes to clean up and to create a hydrophilic (-OH) thin layer for hydrogen bonding. Two different processes of heat treatment performed in succession transformed the hydrogen bonding into direct bonding. The performance of the bonded crystal was tested by laser oscillation with the second harmonics of a Q-switched Nd:YAG laser at a 20-Hz repetition rate. In comparison with a normal laser crystal, there were no differences in output power or spatial profile in an input pumping condition of 30 mJ.     

Protective materials for subpicosecond Ti:sapphire lasers

The high intensities provided by short-pulse Ti:sapphire laser systems call for the utilization of appropriate eye-protecting materials. We summarize the representative results of our characterization measurements on optical filters employed for laser radiation protection. Physical effects are discussed that influence the transmission (and thus the protective properties) of the investigated materials. Potential hazard factors have been recognized and characterized. We make recommendations to the extension of the current characterization methods and illustrate the acquired information in the form of operation charts.     

Amplified spontaneous emission in a Ti:sapphire regenerative amplifier

Amplified spontaneous emission power and contrast ratio in a linear miltipass Ti:sapphire regenerative amplifier with a wavelength centered at 1054 nm are calculated and measured. It is shown that the passive losses of a seed pulse and the losses in coupling to the regenerative amplifier cavity mode degrade the intensity contrast ratio to 10(-6)-10(-7). The advantage of an optical parametric chirped pulse amplifier with respect to the contrast ratio is discussed.     

Efficient pulsed 946-nm laser emission from Nd:YAG pumped by a titanium-doped sapphire laser

Efficient pulsed room-temperature laser emission at 946 nm is obtained from a Nd:YAG rod pumped by a Ti-doped sapphire laser in the free-running mode. Three bonded YAG rods of 3-mm diameter with different Nd concentrations and active lengths were tested. A maximum output energy of 83.5 mJ at 3 Hz was obtained with a slope efficiency of 32.3% in an end-pumping configuration.     

Low-threshold, single-frequency, coupled cavity Ti:sapphire laser

A novel coupled resonator was developed for narrow-bandwidth, tunable, solid-state lasers. Stable, single-longitudinal-mode, gain-switched titanium:sapphire pulses were obtained across a 130-nm operating range limited by the cavity optics. The low threshold fluence of 0.7 Jcm(-2) makes the cavity attractive for other tunable laser media, particularly when gain is low or parasitic loss is high. A model has been developed that can be used to predict the mode structure of the coupled cavity and for optimization at specific wavelength regions.     

Single-longitudinal-mode scan of a pulsed double-grating Ti:sapphire oscillator

The method of the single-longitudinal-mode (SLM) scan of a pulsed double-grating Ti:sapphire laser oscillator with the grazing incidence cavity configuration was proposed based on the analysis of the optical path length. The SLM scan was experimentally confirmed for this cavity configuration, where the second grating was rotated around an arbitrary point with the translational scan of a back mirror.     

Pulsed Ti:sapphire laser seeded off the gain peak

An external-cavity diode laser is used to seed a pulsed Ti:sapphire laser from 839 to 860 nm. Because this wavelength range is off the gain peak of Ti:sapphire, a bandpass filter is used in the cavity to permit seeded operation. We describe a tunable, wide-field-of-view birefringent filter especially suited for use in seeded lasers. Measurements of the ratio of unseeded to seeded output as a function of seed power are also presented and demonstrate an approximately reciprocal dependence on the seed power.     

Single-frequency, high-power, continuous-wave fiber-laser-pumped Ti:sapphire laser

We demonstrate a high-power, continuous-wave (cw), single-frequency green source based on single-pass second-harmonic generation of a Yb-fiber laser in MgO:sPPLT as a viable pump source for a cw single-frequency Ti:sapphire ring laser. By careful design and optimization, the Ti:sapphire laser can provide as much as 2.3 W of cw single-frequency output across a 47 nm tuning range, limited by the reflectivity of the cavity mirrors. By implementing active stabilization of the laser frequency to an external reference, an ultrastable Fabry-Perot interferometer, we obtain a frequency stability better than 12 MHz over 10 min and continuous tunability greater than 180 MHz. Stable output power with peak-to-peak fluctuation of 5.4% over 75 min, in high spatial beam quality with M(2)<1.34, is achieved.     

Ti:sapphire laser cavity mode and pump-laser mode calculations

Comprehensive calculations of the cavity mode size throughout a Ti:sapphire laser, made with the ABCD Gaussian beam formalism are reported. These calculations show that the beam is not collimated, in general, in what are normally referred to as the collimated arms of the laser cavity. Additionally, the mode size and volume (in the gain medium) of the argon-ion laser, which is used to pump the Ti:sapphire laser optically, are evaluated for different focusing geometries, and graphs that can be used to select suitable mode-matching optics are produced. It is concluded that an appropriate strategy for mode matching the pump beam to the Ti:sapphire laser mode is to use a zoom telescope to tailor the collimated pump-laser beam diameter to an optimum value. Finally, comparisons of the pump-laser mode and the Ti:sapphire laser mode are presented for selected pumping geometries.     

Self-seeding of a pulsed double-grating Ti:sapphire laser oscillator

A self-seeded pulsed double-grating Ti:sapphire laser oscillator consisting of a grazing incidence cavity geometry with a pair of gratings and a standing-wave cavity pumped by a frequency-doubled Nd:YAG laser was developed and characterized. With self-seeding, narrow-linewidth single-longitudinal-mode (SLM) operation and SLM scanning were possible with a reduced lasing threshold, which was desirable for the intended applications.     

用飞秒Ti：sapphire激光测定对称型化合物的双光子吸收和上转换荧光

用800nm波长的飞秒Ti:sapphire激光测定了2个对称型噁二唑衍生物2,5-二[4-(2-N,N-二苯氨基苯乙烯基)苯基]-1,3,4-噁二唑(PASPO)与2,5-二[4-{2-N,N-二(4-溴代苯)氨基苯乙烯基]苯基}-1,3,4-噁二唑(BrPASPO)的双光子吸收和双光子激发荧光光谱,其飞秒双光子吸收截面为20.6和9.91GM,双光子泵浦上转换荧光最大波长分别在535和545nm.测定了紫外吸收、荧光光谱,研究了化合物在不同溶剂中的溶致变色效应.化合物PASPO和Br-PASPO在二氯甲烷溶液中的吸收峰分别位于412和403nm,荧光发射峰分别位于511和495nm,荧光量子产率分别为0.73和0.70.