Continuous-wave, two-crystal, singly-resonant optical parametric oscillator: Theory and experiment

Abstract

We present theoretical and experimental study of a continuous-wave, two-crystal, singly-resonant optical parametric oscillator (T-SRO) comprising two identical 30-mm-long crystals of MgO:sPPLT in a four- mirror ring cavity and pumped with two separate pump beams in the green. The idler beam after each crystal is completely out-coupled, while the signal radiation is resonant inside the cavity. Solving the coupled amplitude equations under undepleted pump approximation, we calculate the maximum threshold reduction, parametric gain acceptance bandwidth and closest possible attainable wavelength separation in arbitrary dual-wavelength generation and compare with the experimental results. Although the T-SRO has two identical crystals, the acceptance bandwidth of the device is equal to that of a single-crystal SRO. Due to the division of pump power in two crystals, the T-SRO can handle higher total pump power while lowering crystal damage risk and thermal effects. We also experimentally verify the high power performance of such scheme, providing a total output power of 6.5 W for 16.2 W of green power at 532 nm. We verified coherent energy coupling between the intra-cavity resonant signal waves resulting Raman spectral lines. Based on the T-SRO scheme, we also report a new technique to measure the temperature acceptance bandwidth of the single-pass parametric amplifier across the OPO tuning range.

Controlled switching of orbital angular momentum in an optical parametric oscillator

“…OPOs are recognized as versatile sources of coherent radiation providing high power and broad wavelength coverage from a single device, in all time-scales from continuous-wave (cw) to the femtosecond domain [19][20][21]. Therefore, direct generation and control of OAM modes in an OPO can offer an intriguing route to provide high-power OAM beams at arbitrary wavelengths.…”

Two-crystal, synchronously pumped, femtosecond optical parametric oscillator

“…While the primary goal of our earlier experiments on twocrystal OPOs has so far been arbitrary dual-wavelength generation, it would be desirable to also explore the feasibility of exploiting the concept to achieve further improvements in the OPO performance, for example, with regard to gain, efficiency, and output power enhancement. This can, in principle, be attained through intracavity optical parametric amplification (IOPA) of the circulating signal field in both crystals when operating at identical wavelengths, as observed in our earlier experiments on a two-crystal cw OPO in a single optical cavity [13,14]. In femtosecond OPOs, the exploitation of IOPA can be particularly advantageous for gain and efficiency enhancement because of the restrictions imposed by the spectral acceptance bandwidth (SAB) and group velocity mismatch (GVM) on the maximum usable interaction length of the nonlinear crystal for efficient parametric conversion.…”

“…In critically phase-matched configurations, spatial walkoff is another factor restricting the useful interaction length, since the relatively low intensities associated with high-repetition-rate pump pulses demand tight focusing. On the other hand, by deploying multiple thin nonlinear crystals, one can circumvent such limitations and maintain the same SAB, GVM and spatial walkoff as that of a single crystal of short length [14], while increasing the total effective interaction length for parametric gain, thus enhancing the efficiency and output power through IOPA. Here, we demonstrate this concept in a femtosecond OPO deploying a single optical cavity with two thin identical MgO:PPLN nonlinear crystals that are pumped in synchronization with two input pulse trains from the same Kerr-lens-mode-locked (KLM) Ti:sapphire laser.…”

“…Traditionally, all such ultrafast OPOs deploy a single nonlinear crystal as the gain element within a cavity that is synchronously driven by a single input pump pulse train. In a departure from this conventional approach, we previously demonstrated that the inclusion of a second nonlinear crystal in an OPO cavity can offer additional advantages, such as enhanced wavelength flexibility, while maintaining robust and practical performance of the device with regard to all important operating parameters including output power, efficiency, power stability, as well as spectral and spatial beam quality [11][12][13][14][15]. We demonstrated successful operation of OPOs in both femtosecond [11] and picosecond [12] time-scale, as well as in continuous-wave (cw) regime [13][14][15], using two-crystal configurations, enabling dual-wavelength signal-idler pair generation with independent and arbitrary tuning across broad spectral regions.…”

“…While in synchronously pumped femtosecond operation, we employed an antiresonant ring (ARR) interferometer to connect the two resonators [11], and in picosecond operation, we used a single optical cavity for the two-crystal OPO [12]. In the cw regime, we demonstrated the concept using both a single optical cavity [13,14] and an ARR to couple the two OPOs [15]. While the primary goal of our earlier experiments on twocrystal OPOs has so far been arbitrary dual-wavelength generation, it would be desirable to also explore the feasibility of exploiting the concept to achieve further improvements in the OPO performance, for example, with regard to gain, efficiency, and output power enhancement.…”