Jan-Peter Meyn

Fourier-transform external cavity lasers

We explore the potential of a new laser resonator design that uses an intracavity Fourier transformation and allows for multi-color operation, gain extension and intracavity second harmonic generation (SHG). First, purely electronically controlled wavelength tuning is demonstrated using liquid crystal displays (LCDs) and digital mirror devices. Moreover, the new design can be applied to different lasers as shown on the examples of a laser diode and a Thulium-doped fiber laser in the mid-infrared. Furthermore, we demonstrate the simultaneous control of multiple gain media within one single external cavity. In addition, tunable emission in the 490 nm range is obtained using intracavity SHG with one single control parameter. Finally, we unambiguously prove simultaneous multi-wavelength operation with variable wavelength spacings and apply it to the generation of THz difference frequencies.

Single-frequency continuous-wave optical parametric oscillator system with an ultrawide tuning range of 550 to 2830 nm

We present a cw single-frequency laser source with what is to our knowledge the largest emission range ever demonstrated, from the green to the mid-IR range. It employs a cw optical parametric oscillator with subsequent resonant frequency doubling. Typical output powers are 30–500 mW, with 160 mW at 580 nm. Mode-hop-free oscillation, high absolute frequency stability, 20-kHz-signal linewidth, and up to 38-GHz continuous tuning are demonstrated. Both PPLN and PPKTP are used as nonlinear materials, and their performance is compared.

Singly resonant continuous-wave optical parametric oscillator pumped by a diode laser

We report on what is believed to be the first singly resonant cw optical parametric oscillator (SRO) that is directly pumped by a diode laser. The SRO consists of a 38-mm-long periodically poled LiNbO3 crystal in a four-mirror signal-resonant ring cavity. Pumped by 2.5 W of 925-nm diode-laser radiation, the SRO generates 480 mW of single-frequency idler radiation at 2.1 µm. The wavelengths of the signal and the idler output are tuned in the ranges of 1.55 to 1.70 µm and 2.03 to 2.29 µm, respectively, by tuning the wavelength of the diode laser from 924.0 to 925.4 nm.

Periodically poled potassium niobate for second-harmonic generation at 463 nm.

We report on the fabrication and characterization of quasi-phase-matched potassium niobate crystals for second-harmonic generation. Periodic 30-mum -pitch antiparallel ferroelectric domains are fabricated by means of poling in an electrical field. Both birefrigence and periodic phase shift of the generated second harmonic contribute to phase matching when the d(31) nonlinear optical tensor element is used. 3.8 mW of second-harmonic radiation at 463 nm is generated by frequency doubling of the output of master-oscillator power-amplifier diode laser in a 5-mm-long crystal. The measured effective nonlinear coefficient is 3.7pm/V. The measured spectral acceptance bandwidth of 0.25 nm corresponds to the theoretical value.

Nanosecond periodically poled lithium niobate optical parametric generator pumped at 532 nm by a single-frequency passively Q-switched Nd:YAG laser.

We report an efficient, visible, nanosecond optical parametric generator of periodically poled lithium niobate pumped at 532 nm by a frequency-doubled, diode-pumped, passively Q -switched, single-mode Nd:YAG laser with 90-muJ pulse energy. The signal radiation is tunable from 637 to 593 nm. The maximum signal-conversion efficiency is 23%. Optical parametric amplification of a He-Ne laser at 632.8 nm is also studied.

Generation of sub-6-fs blue pulses by frequency doubling with quasi-phase-matching gratings

We demonstrate the generation of sub-6-fs pulses centered at 405 nm by frequency doubling of 8.6-fs Ti:sapphire laser pulses. The frequency doubling is carried out in a nonlinearly chirped quasi-phase-matching grating fabricated in a lithium tantalate substrate. This device simultaneously provides frequency conversion and pulse compression of the positively prechirped fundamental pulses. The second-harmonic pulses are characterized in a cross-correlation setup, and their pulse shapes are retrieved by two iterative phase-reconstruction algorithms. The generated second-harmonic spectrum spans a bandwidth of 220 THz. To our knowledge, these are the shortest pulses ever generated in the blue spectral region.

Diode-pumped continuous-wave widely tunable optical parametric oscillator based on periodically poled lithium tantalate.

We report on a diode-laser pumped cw optical parametric oscillator (OPO) based on quasi-phase-matched periodically poled lithium tantalate. Pumped by the 2.3-W single-frequency, nearly diffraction-limited 925-nm output of an InGaAs diode master-oscillator power amplifier, the pump and signal resonant OPO generates a single-frequency idler wave with an output of as much as 244 mW. The wavelengths of the signal and idler waves are widely tunable in the range 1.55-2.3mum by use of different poling periods (27.3 to 27.9mum) and by variation of the crystal temperature in the range 70-190 degrees C.

Single-frequency continuous-wave radiation from 0.77 to 1.73 µm generated by a green-pumped optical parametric oscillator with periodically poled LiTaO 3

We describe a cw optical parametric oscillator (OPO) with multigrating periodically poled LiTaO(3) . Pumped by a single-frequency 532-nm laser, the OPO emits single-frequency radiation at wavelengths from 0.77 to 1.73 microm with as much as 60 mW of output power. Mode-hop-free operation for as long as 50 min, a low frequency drift (<70 MHz/h), and as much as 700-MHz continuous frequency tuning of signal and idler are demonstrated.

Self-injection-locking of a CW-OPO by intracavity frequency-doubling the idler wave

We report on the observation of self-injection-locking of the signal wave of an optical parametric oscillator (OPO) with the intracavity frequency doubled idler wave. The two-mirror OPO is based on a periodically poled LiNbO3 (PPLN) crystal and pumped with a grating stabilized, continuous-wave (CW) single-frequency diode master-oscillator power-amplifier (MOPA) system. Simultaneous quasi-phase-matching (QPM) of OPO and second harmonic generation (SHG) is provided in the same crystal which carries two different domain gratings. The beat of the signal wave and the frequency-doubled idler wave is suppressed within a 500-kHz wide frequency range centered around zero as expected for self-injection- locking. The measurements prove the feasibility of optically phase-stabilized by-three-division of an optical frequency with CW-OPOs using cascaded nonlinearities.

Electro-optic modification of second-harmonic phase-matching spectra in segmented periodically poled LiNbO3

We demonstrate a method that enables in situ modification of the spectral shape of the parametric-gain profile in quasi-phase-matching crystals. In our experiment we used the electro-optic effect to modify the phase-matching profile for second-harmonic generation in a 57-mm-long nonuniformly poled LiNbO3 crystal. In the direction of beam propagation the crystal is divided into three segments, where the first and the third segments have an equal length of 17 mm. Both segments are periodically poled with the same period of 21.6 µm, in order to obtain quasi phase matching for frequency doubling a fundamental wavelength of 1653 nm. The center segment is single-domain LiNbO3 whose index of refraction is changed by the electro-optic effect by applying a voltage. Using a continuously tunable, single-frequency, single-stripe, distributed-feedback diode laser as the fundamental source, we recorded the parametric phase-matching profile for second-harmonic generation as a function of the laser wavelength and investigated the modification of the profile in dependence of the voltage applied to the crystal center segment. The measured phase-matching spectra are in excellent agreement with the theoretical prediction. The demonstrated method opens the possibility of rapidly changing the parametric-gain profile for all types of χ(2) nonlinear conversion processes.