G. K. Samanta

Stable, 9.6 W, continuous-wave, single-frequency, fiber-based green source at 532 nm

We present a stable, high-power, cw, single-frequency green source in a compact and practical design based on a simple single-pass second-harmonic generation of a cw ytterbium fiber laser at 1064 nm in MgO-doped periodically poled stoichiometric LiTaO(3). Using a 30-mm-long crystal containing a single grating, we have generated 9.64 W of cw radiation at 532 nm with a fundamental power of 29.5 W at a single-pass conversion efficiency of 32.7%. The output power is naturally stable with a peak-to-peak fluctuation of 7.6% over the first 8 h and 9% over 13 h. Over the entire range of fundamental powers, the generated green output is single frequency with an instantaneous linewidth of 6.5 MHz and frequency stability of <32 MHz over 30 min and has a TEM(00) spatial profile with M(2)<1.33.

High-power, single-frequency, continuous-wave second-harmonic-generation of ytterbium fiber laser in PPKTP and MgO:sPPLT

Characteristics of high-power, narrow-linewidth, continuous-wave (cw) green radiation obtained by simple single-pass second-harmonic-generation (SHG) of a cw ytterbium fiber laser at 1064 nm in the nonlinear crystals of PPKTP and MgO:sPPLT are studied and compared. Temperature tuning and SHG power scaling up to nearly 10 W for input fundamental power levels up to 30 W are performed. Various contributions to thermal effects in both crystals, limiting the SHG conversion efficiency, are studied. Optimal focusing conditions and thermal management schemes are investigated to maximize SHG performance in MgO:sPPLT. Stable green output power and high spatial beam quality with M(2)<1.33 and M(2)<1.34 is achieved in MgO:sPPLT and PPKTP, respectively.

1.59 W, single-frequency, continuous-wave optical parametric oscillator based on MgO:sPPLT

A watt-level, single-frequency, continuous-wave (cw) singly resonant optical parametric oscillator (OPO) based on MgO:sPPLT is described. Pumped in the green by a frequency-doubled cw diode-pumped Nd:YVO(4) laser at 532 nm, the OPO can provide up to 1.59 W of single-frequency idler output with a linewidth of ~7 MHz at pump depletions of as much as 67%. Using a compact ring resonator and optimized focusing in a 30 mm crystal, a singly resonant oscillation threshold of 2.84 W has been obtained under single-pass pumping. With a single grating period of 7.97 microm, continuous signal and idler coverage over 852-1417 nm is obtained by temperature tuning between 61 degrees C and 236 degrees C. The influence of thermal lensing on idler output power across the SRO tuning range is also verified.

High-power, continuous-wave, singly resonant optical parametric oscillator based on MgO:sPPLT

High-power, continuous-wave (cw) mid-infrared optical parametric oscillators (OPOs) are of prime interest for variety of applications including spectroscopy and trace gas detection, requiring wide tunability and narrow linewidth. Singly-resonant OPOs (SROs) based on quasi-phase-matched(QPM) nonlinear materials such as MgO:PPLN represent the most viable configuration for such applications, because of high output power and simplified tuning. However, overcoming detrimental thermal effects is still a challenge [1]. The emergence of new QPM ferroelectric materials such as MgO-doped stoichiometric periodically-poled LiTaO3 (MgO:sPPLT), with improved optical and thermal properties [2], has lead to very important advances [3]. Also, cw SROs based on MgO:sPPLT, pumped in the green, have been previously demonstrated [3,4]. In spite of a lower effective nonlinear coefficient (deff∼9 pm/V) than PPLN (deff∼16 pm/V), increased resistance to photorefractive damage and better thermal conductivity in MgO:sPPLT make it an attractive new alternative to overcome performance limitations due to thermal effects. Hence, it would be of great interest to explore the feasibility of using MgO:sPPLT in cw SROs pumped at 1064 nm, for the generation of high optical powers in the mid-infrared.

High-efficiency, multicrystal, single-pass, continuous-wave second harmonic generation

We describe the critical design parameters and present detailed experimental and theoretical studies for efficient, continuous-wave (cw), single-pass second harmonic generation (SHG) based on novel cascaded multicrystal scheme, providing >55% conversion efficiency and multiwatt output powers at 532 nm for a wide range of input fundamental powers at 1064 nm. Systematic characterization of the technique in single-crystal, double-crystal and multicrystal schemes has been performed and the results are compared. Optimization of vital parameters including focusing and phase-matching temperature at the output of each stage is investigated and strategies to achieve optimum SHG efficiency and power are discussed. Relevant theoretical calculations to estimate the effect of dispersion between the fundamental and the SH beam in air are also presented. The contributions of thermal effects on SHG efficiency roll-off have been studied from quasi-cw measurements. Using this multicrystal scheme, stable SH power with a peak-to-peak fluctuation better than 6.5% over more than 2 hours is achieved in high spatial beam quality with M2<1.6.

High-power, continuous-wave, second-harmonic generation at 532 nm in periodically poled KTiOPO 4

We report efficient generation of high-power, cw, single-frequency radiation in the green in a simple, compact configuration based on single-pass, second-harmonic generation of a cw ytterbium fiber laser at 1064 nm in periodically poled KTiOPO(4). Using a crystal containing a 17 mm single grating with period of 9.01 microm, we generate 6.2 W of cw radiation at 532 nm for a fundamental power of 29.75 W at a single-pass conversion efficiency of 20.8%. Over the entire range of pump powers, the generated green output is single frequency with a linewidth of 8.5 MHz and has a TEM(00) spatial profile with M(2)<1.34. The demonstrated green power can be further improved by proper thermal management of crystal heating effects at higher pump powers and also by optimized design of the grating period to include thermal issues.

Multicrystal, continuous-wave, single-pass second-harmonic generation with 56% efficiency

We report a simple and compact implementation for single-pass second-harmonic-generation (SP-SHG) of cw laser radiation, based on a cascaded multicrystal (MC) scheme, that can provide the highest conversion efficiency at any given fundamental power. By deploying a suitable number of identical 30-mm-long MgO:sPPLT crystals in a cascade and a 30W cw Yb-fiber laser at 1064nm as the fundamental source, we demonstrate SP-SHG into the green with a conversion efficiency as high as 56% in the low-power as well as the high-power regime, providing 5.6W of green output for 10W and 13W of green output for 25.1W of input pump power. The MC scheme permits substantial increase in cw SP-SHG efficiency compared to the conventional single-crystal scheme without compromising performance with regard to power stability and beam quality.

Continuous-wave, single-frequency, solid-state blue source for the 425–489 nm spectral range

We report a new source of cw, single-frequency radiation in the blue, offering extended tunability and practical powers in a compact, all-solid-state design. The device is based on a green-pumped, cw, singly resonant optical parametric oscillator using MgO-doped stoichiometric lithium tantalate (MgO:sPPLT) as the nonlinear material. By internal second-harmonic generation of the resonant near-infrared signal radiation in a 5 mm BiB(3)O(6) crystal, we generate nearly 450 mW of cw, single-frequency blue power over a tunable range of 425-489 nm with a linewidth of 8.5 MHz and a Gaussian spatial beam profile. The demonstrated wavelength coverage can be further extended by using alternative gratings for the MgO:sPPLT crystal.

Continuous-wave singly-resonant optical parametric oscillator with resonant wave coupling.

We report major enhancements in the overall performance of continuous-wave singly-resonant optical parametric oscillators (cw SROs) through finite output coupling of the resonant wave. Using a cw SRO based on MgO:sPPLT pumped at 532 nm, we demonstrate improvements of 1.08 W in total output power, 10% in total extraction efficiency, and a 130-nm extension in the useful tuning range, while maintaining pump depletions of 70%, idler output powers of 2.59 W, and a minimal increase in oscillation threshold of 24%. The output-coupled cw SRO can deliver a total power of up to 3.6 W at 40% extraction efficiency across 848-1427 nm. The single-frequency resonant wave also exhibits a higher spectral purity than the non-resonant output.

Continuous-wave optical parametric oscillator pumped by a fiber laser green source at 532 nm.

We report a high-power, cw, singly resonant optical parametric oscillator (SRO) using a simple, compact fiber pump laser architecture in the green. The SRO, based on MgO:sPPLT, is pumped by 9.6 W of single-frequency cw radiation at 532 nm obtained by single-pass second-harmonic generation (SHG) of a 30 W Yb fiber laser, also in MgO:sPPLT. Using two identical crystals of 30 mm length for SHG and SRO, we generate cw idler powers of up to 2 W over 855-1408 nm, with a peak-to-peak power stability <11.7% over 40 min, in a TEM(00) spatial mode with M(2)<1.26. Using finite output coupling of the resonant wave, we extract 800 mW of signal power with peak-to-peak power stability <10.7% over 40 min, and a frequency stability <75 MHz over 15 min. The signal and idler output have TEM(00) beam profile with M(2)<1.52 across the tuning range.