Extended mode-hop-free tuning by use of a dual-cavity, pump-enhanced optical parametric oscillator

1.8 W, high efficiency, pump-enhanced, narrow linewidth optical parametric oscillator at 3.8 µm

A high efficiency, continuous-wave, narrow linewidth, pump-enhanced optical parametric oscillator (OPO) at 3.8 µm was demonstrated, which was pumped by a 1064 nm fiber laser with a linewidth of 18 kHz. The low frequency modulation locking technique was employed to stabilize the output power. The wavelengths of signal and idler were 1475.5 nm and 3819.9 nm at 25 °C, respectively. The pump-enhanced structure was applied, leading to a maximum quantum efficiency of over 60% with pump power of 3 W. The maximum output power of idler light is 1.8 W with a linewidth of 363 kHz. The excellent tuning performance of the OPO was also demonstrated. In order to avoid mode-splitting and decrease of pump enhancing factor due to feedback light in the cavity, the crystal was placed obliquely to the pump beam and the maximum output power was increased by 19%. At the maximum output power of idler light, the M² factors in the x and y directions were 1.30 and 1.33, respectively.

Continuous-wave, singly-resonant, intracavity optical parametric oscillator based on a single-mode-laser-diode-pumped Yb:KYW laser

We report a continuous-wave (cw), intracavity, singly resonant optical parametric oscillator (ICSRO) based on an Yb:KYW laser pumped by a single-mode laser diode (LD). Pumping the ICSRO by a low-noise single-mode LD, combined with the reduced heat generation due to the lower quantum defect of the Yb:KYW laser system, effectively eliminated the onset of relaxation oscillations, which have been a long-standing problem in previous multimode-LD-pumped ICSROs, and resulted in a cw ICSRO being operated free of relaxation oscillations. At an LD power of 515 mW, the generated idler power was 21 mW at ∼3500  nm. To the best of our knowledge, this is the first demonstration of a single-mode-LD-pumped ICSRO.

A continuous-wave optical parametric oscillator around 5-μm wavelength for high-resolution spectroscopy

We present a continuous-wave optical parametric oscillator (OPO) capable of high resolution spectroscopy at wavelengths between 4.8 μm and 5.4 μm. It is based on periodically poled lithium niobate (PPLN) and is singly resonant for the signal radiation around 1.35 μm. Because of the strong absorption of PPLN at wavelengths longer than 4.5 μm, the OPO threshold rises to the scale of several watts, while it produces idler powers of more than 1 mW and offers continuous tuning over 15 GHz. A supersonic jet spectrometer is used in combination with the OPO to perform measurements of the transient linear molecule Si(2)C(3) at 1968.2 cm(-1). Fifty rovibrational transition frequencies of the ν(3) antisymmetric stretching mode have been determined with an accuracy on the order of 10(-4) cm(-1), and molecular parameters for the ground and the v(3) = 1 state have been determined most precisely.

Pump-tunable continuous-wave singly resonant optical parametric oscillator from 2.5 to 4.4 microm

We report a continuous-wave singly resonant optical parametric oscillator pumped by a widely tunable titanium-doped sapphire ring laser. It produces up to 0.8 W of mid-infrared power. The wavelength can be tuned in a few seconds from 2.5 to 3.5 microm or from 3.4 to 4.4 microm and scanned up to 40 GHz without mode-hops by only changing the pump beam wavelength. Spectroscopic capability is demonstrated by measuring parts of the photoacoustic absorption spectrum of NH(3) near 3196 cm(-1).

Pump-enhanced difference-frequency generation at 3.3 microm

The demonstration of continuous wave intracavity difference-frequency generation in the mid-infrared (mid-IR) is presented. A cavity for pump laser enhancement is constructed around a periodically poled lithium niobate crystal, and the cavity length is locked to the frequency of the pump laser using the Pound-Drever-Hall technique, producing a gain of 12 in the resultant idler power compared to the single-pass case. A widely tunable single-mode 3.3 microm idler beam with a power of nearly 10 mW is available for direct absorption spectroscopy. The pump-enhancement method demonstrated here should be readily scalable to produce hundreds of milliwatts of mid-IR light by using higher power signal and pump lasers.

Parts per trillion sensitivity for ethane in air with an optical parametric oscillator cavity leak-out spectrometer

Spectroscopic detection of ethane in the 3-microm wavelength region was performed by means of a cw optical parametric oscillator and cavity leak-out. We achieved a minimum detectable absorption coefficient of 1.6 x 10(-10) cm 1/square root of Hz, corresponding to an ethane detection limit of 6 parts per trillion/square root of Hz. For 3-min integration time the detection limit was 0.5 parts per trillion. The levels are to our knowledge the best demonstrated so far. These frequency-tuning capabilities facilitated multigas analysis with simultaneous monitoring of ethane, methane, and water vapor in human breath.

Compact, continuous-wave, singly resonant optical parametric oscillator based on periodically poled RbTiOAsO4 in a Nd:YVO4 laser

We describe a compact all-solid-state continuous-wave, singly resonant optical parametric oscillator (SRO) based on periodically poled RbTiOAsO4. The SRO is pumped at 1.064 microm by a Nd:YVO4 laser, which is itself pumped by a 3-W diode laser. Using the intracavity technique produced an oscillation threshold for the SRO of only 1.6 W (diode-laser power). For 3 W of diode pump power some 65 mW was obtained in the (nonresonant) idler (wavelength 3.52 microm). Temperature tuning over the range 10-100 degrees C resulted in tuning ranges of 1.52-1.54 and 3.41-3.54 microm for the signal and the idler waves, respectively. Importantly, relaxation oscillations were absent.

Single-mode, tunable output from a midwave-infrared-seeded optical parametric oscillator system

We have built a coupled master oscillator and a slave oscillator optical parametric oscillator (OPO) system that provides single-frequency, pulsed radiation in the midwave infrared (MWIR). The direct-diode-pumped master OPO provided narrow-band (<6-MHz, instrument-limited), tunable MWIR cw radiation that was used to seed a higher-peak-power pulsed slave OPO. When seeded directly at the MWIR idler, the pulsed output of the slave OPO was constrained to oscillate on a single longitudinal mode even though the slave OPO is pumped by a multilongitudinal-mode laser source. The linewidth of the pulsed output has been measured to be <220 MHz (instrument limited), which is well suited for coherent differential absorption lidar applications.

Stable, continuously tunable operation of a diode-pumped doubly resonant optical parametric oscillator

We demonstrate, for what is the first time to our knowledge, long-term stable, continuously tunable operation of a doubly resonant optical parametric oscillator (OPO) pumped by a single-stripe diode laser without the use of an external semiconductor amplifier. The OPO is based on periodically poled lithium niobate and is pumped by a 150-mW distributed Bragg grating diode laser. 18-mW total output power is generated at 1.3- and 2.3-mum wavelengths. A cavity-length servo system allows continuous signal tuning of 17 GHz and idler tuning of 10 GHz, limited only by the range of a piezoelectric cavity mirror mount. OPO tuning is demonstrated from 1.1 to 1.4 mum and from 2.2 to 3.7 mum.