Nanosecond parametric Raman anti-Stokes SrWO4 laser at 507 nm with collinear phase matching.

Collinear phase matching of the Stokes ↔ anti-Stokes interaction for Raman-active crystals with different birefringence was studied theoretically as well as experimentally. It was shown that collinear phase matching of the Stokes ↔ anti-Stokes interaction in low-birefringent crystals can be insensitive to angular mismatch if a phase matching angle is higher than 60°. We have developed and experimentally realized an extracavity parametric Raman anti-Stokes laser based on a low-birefringent SrWO4. Cyan 507-nm anti-Stokes conversion from green (532 nm) pump radiation of a 5-ns, 1-mJ second harmonic Nd:YAG laser has been obtained. Laser setup with a single beam excitation made it possible to use an output face of the SrWO4 crystal as an output coupler because of wide (6°) angular tolerance of collinear phase matching that resulted in an increase of slope efficiency of anti-Stokes generation higher than 3% at the anti-Stokes energy output of a 10-µJ level.

Extracavity pumped parametric Raman nanosecond crystalline anti-Stokes laser at 954 nm with collinear orthogonally polarized beam interaction at tangential phase matching.

The extracavity parametric Raman CaCO3 anti-Stokes laser at 954 nm excited by two orthogonally polarized (pump and probe) equal frequency laser beams was proposed and investigated. Tangential phase matching conditions for the orthogonally polarized Raman components four-wave mixing in the CaCO3 crystal at stimulated Raman scattering (SRS) under 1064-nm excitation were theoretically studied and applied for a novel nanosecond parametric Raman laser allowing to increase the 954-nm anti-Stokes generation efficiency. In agreement with the theoretical modeling, using the high-Q external cavity scheme we have experimentally achieved the highest optical-to-optical (1064 nm to 954 nm) efficiency of 4% in comparison with the known crystalline parametric Raman anti-Stokes lasers. The ~3 ns anti-Stokes output pulse energy was 0.3 mJ with high beam quality factor M2 = 1.1 × 1.2.

Cryogenically-cooled Yb:YGAG ceramic mode-locked laser.

This work reports on a liquid-nitrogen-cooled, SESAM mode-locked Yb:YGAG (Yb:Y(3)Ga(2)Al(3)O(12)) ceramic laser. The Yb:YGAG has a similar structure to Yb:YAG, but its emission spectrum at low temperature remains much broader, which is suitable for ultrashort pulse generation and amplification. A stable pulse train with 119-MHz repetition rate was obtained at a wavelength of 1026 nm. The measured pulse duration is 2.4 ps, which is more than four times shorter than that achieved with a cryogenically-cooled Yb:YAG. Furthermore, laser performance of the Yb:YGAG ceramics in continuous-wave operation and wavelength tunability at 80 K was investigated.

2-µm wavelength, high-energy Ho:YLF chirped-pulse amplifier for mid-infrared OPCPA.

A 2-µm wavelength laser delivering up to 39-mJ energy, ∼10 ps duration pulses at 100-Hz repetition rate is reported. The system relies on chirped pulse amplification (CPA): a modelocked Er:Tm:Ho fiber-seeder is followed by a Ho:YLF-based regenerative amplifier and a cryogenically cooled Ho:YLF single pass amplifier. Stretching and compressing are performed with large aperture chirped volume Bragg gratings (CVBG). At a peak power of 3.3 GW, the stability was <1% rms over 1 h, confirming high suitability for OPCPA and extreme nonlinear optics applications.

Tunable, high-energy, mid-infrared, picosecond optical parametric generator based on CdSiP2.

We report a tunable, high-energy, single-pass optical parametric generator (OPG) based on the nonlinear material, cadmium silicon phosphide, CdSiP(2). The OPG is pumped by a cavity-dumped, passively mode-locked, diode-pumped Nd:YAG oscillator, providing 25 µJ pulses in 20 ps at 5 Hz. The pump energy is further boosted by a flashlamp-pumped Nd:YAG amplifier to 2.5 mJ. The OPG is temperature tunable over 1263-1286 nm (23 nm) in the signal and 6153-6731 nm (578 nm) in the idler. Using the single-pass OPG configuration, we have generated signal pulse energy as high as 636 µJ at 1283 nm, together with idler pulse energy of 33 µJ at 6234 nm, for 2.1 mJ of input pump pulse energy. The generated signal pulses have durations of 24 ps with a FWHM spectral bandwidth of 10.4 nm at central wavelength of 1276 nm. The corresponding idler spectrum has a FWHM bandwidth of 140 nm centered at 6404 nm.

High-power diode-pumped picosecond Nd(3+):YVO(4) laser.

A diode-pumped Nd(3+):YVO(4) laser passively mode locked by a nonlinear mirror based on second-harmonic generation has been developed. Pumping with a fiber-coupled 10-W diode array, we generated nearly diffraction limited, linearly polarized 11-ps pulses at 1064nm, with average power of 2.7 W at a 150-MHz repetition rate. Pulses as short as 7.9 ps were measured with reduced output power (1.35 W) by optimal focusing in the nonlinear crystal.

Percutaneous laser angioplasty with a pulsed Nd:YAG laser. Initial clinical experience and early follow-up.

Percutaneous laser-assisted balloon angioplasty with a pulsed Nd:YAG laser coupled to sapphire tipped optical fibers was used for the treatment of 22 patients presenting with 30 chronic occlusions of peripheral arteries (mean length 11 cm) during 25 sessions. The procedure was completed by balloon dilatation in 67%. Successful recanalization was achieved in 92%, clinically the procedure was successful in 68% with mean ABPI increase from 0.43 +/- 0.13 to 0.79 +/- 0.21. In 8 cases complications occurred. Two reocclusions were treated by streptokinase infusion, and 2 procedures were repeated 2 months later, one patient was referred to elective bypass surgery, and 3 patients were treated conservatively. Six patients were followed-up for more than 6 months. In 1 patient claudication of 400 m reappeared. These results are encouraging and it is likely that this method could become an important adjunct to balloon angioplasty.

Mode locking of a Nd:YAlO(3) laser at the 1.34-microm transition by a second-harmonic nonlinear mirror.

A second-harmonic nonlinear mirror formed by a LiIO(3) frequency doubler and a dichroic output mirror is employed to mode lock the 1.34-microm transition of a pulsed Nd:YAlO(3) laser. Pulses of 15-ps duration are reliably generated simultaneously at 1.34 and 0.67 microm.

[Percutaneous recanalization of the femoral artery using a laser]. / Perkutánní rekanalizace femorální tepny laserem.

The authors performed, in the period from February to May 1989 seven recanalization interventions on occlusions of femoral artery with a laser angioplasty. In six cases the dilatation of the formed primary canal was made by subsequent balloon angioplasty. In all patients the intervention was followed by a significant clinical improvement and increased doppler index. No significant clinical complications occurred during the interventions.

Active-passive mode-locked Nd:YAG laser with passive negative feedback.

Stationary ultrashort light pulses of 10-psec duration and with an energy of 10 microJ per pulse were obtained from an active-passive mode-locked Nd:YAG laser by using a two-photon absorption limiter (GaAs) inserted into the resonator. The stability of energy in the steady-state part of the pulse train, containing approximately 90 pulses, is better than +/-1.5%. The dynamics of the pulse-shortening mechanism are described, and it is shown that maximum pulse compression is reached after only approximately 10 round trips.

Nearly on-line picosecond streak camera diagnostics of the cw mode-locked YAG laser radiation.

An image-converter streak camera incorporating a TV video-recording system interfaced to a computer HP 2100 was used to record and instantly display the processed shape of a picosecond laser pulse. The output versus input exposure response curve linearity of the whole system was verified over a dynamic range of at least 10. Performance testing of the system was done using a cw mode-locked YAG laser.