Jens Aage Tellefsen

Diode-pumped Er–Yb:glass laser passively Q switched by use of Co 2+ :MgAl 2 O 4 as a saturable absorber

We report on passively Q-switched operation of a diode-pumped Er-Yb:glass laser with a Co(2+):MgAl(2)O(4) plate as a saturable absorber. Optical pulses with peak power exceeding 2 kW and a pulse length of 2.3 ns have been generated. Single-longitudinal-mode Q-switched operation at 1.53 mum has been obtained by use of the Co(2+):MgAl(2)O(4) plate as an intracavity etalon. A discussion of the optimal Er(3+) concentration as well as optimization of the cavity design is included.

Efficient Nd:YAG Laser Frequency Doubling with Periodically Poled KTP.

Periodically poled flux-grown KTiOPO(4) was used for efficient extracavity 1064-nm Nd:YAG laser frequency doubling. A conversion efficiency exceeding 65% was obtained in Q-switched operation, and 1.34 W of average frequency-doubled power was generated with 2.2 W of mode-locked laser output. The conversion efficiency is approximately two times higher for periodically poled KTP than for conventional type II phase-matched KTP. The measurements indicate that periodically poled KTP is less susceptible to optical damage than type II KTP.

Hybrid diode-laser fiber-amplifier source of high-energy ultrashort pulses

We demonstrate what we believe is the first compact laser system for generating ultrashort microjoule-energy optical pulses. Linearly chirped pulses from monolithic tunable Bragg-reflection laser diodes were amplified in a diode-pumped two-stage erbium-doped fiber amplifier and compressed with a grating-pair compressor. The laser diodes had their emission wavelengths at 1.538 and 1.562 microm. The highest pulse energies obtained were 2 microJ at the repetition frequencies of 1-10 kHz and were at the saturation energy level of the fiber amplifier. The shortest duration of compressed pulses is 1.8 ps.

NONCOLLINEAR SECOND-HARMONIC GENERATION IN PERIODICALLY POLED KTIOPO4 EXCITED BY THE BESSEL BEAM

Frequency doubling in periodically poled KTiOPO(4) excited by the Bessel-like distribution of the fundamental radiation has been investigated. Theoretical analysis and experiments show that the use of noncollinear geometry provides new possibilities for engineering nonlinear interactions in periodically poled crystals. We demonstrate conversion of the ring-shaped fundamental mode to the axial second-harmonic beam with 30% efficiency for 220-muJ Q -switched Nd:YAG pulses.

Generation of femtosecond optical pulses with nanojoule energy from a diode laser and fiber based system

Linearly chirped, subnanosecond optical pulses, emitted at an arbitrary repetition rate by a fast‐tuned monolithic diode laser, were compressed down to 600 fs by group‐velocity dispersion in a standard optical fiber. Subsequent amplification and nonlinear compression in an erbium‐doped fiber amplifier produced pulses with the energy of up to 2 nJ and the duration down to 230 fs.

Real-time picosecond electro-optic oscilloscope technique using a tunable semiconductor laser

The feasibility of using a tunable semiconductor laser for real‐time electro‐optic measurements of picosecond electrical signals is demonstrated. The method is based on real‐time amplitude modulation of a relatively long optical probe pulse, whose frequency is linearly swept (chirped) to provide temporal information. Such chirped optical probe pulses were obtained by fast tuning of the emission wavelength of a three‐sectional distributed‐Bragg‐reflector diode laser. An electrical‐pulse rise time of 18 ps was measured. Temporal‐resolution limitations of this type of electro‐optic oscilloscope are discussed.

Design of fiber gratings for total dispersion compensation.

An optical fiber grating has theoretically been designed that would be capable of compressing a dispersionbroadened pulse of 100 ps down to the transform limit of 20 ps, with a total reflectance of ~75%. A numerical recipe is presented for the design of a fiber grating, whose spectral response closely follows an arbitrarily chosen profile, both for the reflectance and the phase factor. The resulting grating consists of a number of subgratings, all of which have the same grating period but a different spatial phase and coupling coefficient.

Q-switching of an Er–Yb:glass microchip laser using an acousto-optical modulator

Abstract We present a compact Q-switched Er–Yb:glass microchip laser operating at the wavelength of 1.535 μm using an acousto-optical modulator. A Q-switched peak power of 325 W with a pulse-duration of 38 ns and a pulse-to-pulse jitter of less then 10 ns was achieved. Well-controlled pulses were obtained for repetition rates up to 10 kHz while the maximum pulse energy was 12 μJ. The experimental results are compared with theoretical analysis, which shows how to optimize the laser as well as fundamental limitations.

Singly resonant optical parametric oscillator in periodically poled KTiOPO 4 pumped by a Bessel beam

Conical pumping was used in a periodically poled KTiOPO(4) optical parametric oscillator for singly resonant idler generation in a nearly diffraction-limited axial beam. A single signal-idler pair was generated over the whole tuning range by use of asymmetric reflectivity of the OPO mirrors. Pump depletion of 40% and total conversion efficiency of 27% were obtained. Additional OPO tuning capability was demonstrated by adjustment of the angle of the conical pump beam.

Noncollinear frequency conversion in the PPKTP

Summary form only given. Noncollinear interaction in birefringence phase-matched nonlinear crystals is usually used for the tuning of the output wavelength and group-velocity matching in short pulse optical parametric generators. The output beam shaping in travelling wave optical parametric generator (TOPG) with bulk crystal pumped by a Bessel beam in multiple noncollinear phase matching geometry has been demonstrated. In periodically poled KTiOPO/sub 4/ (KTP) (PPKTP) the effective nonlinear coefficients are several times larger than in the case of birefringence phase-matching. So relatively low parametric generation threshold has been demonstrated recently. We have investigated the second harmonic (SH) generation in PPKTP crystal pumped by Bessel beam in multiple noncollinear phase matching geometry.