Double-pass Pump Configuration Research Articles

High-performance cavity-dumped Q-switched Alexandrite laser CW diode-pumped in double-pass configuration.

We present a high-performance Alexandrite laser for LIDAR applications with repetition rates up to 20 kHz in cavity-dumped Q-switched operation continuous-wave diode-pumped in the red spectral region. With a double-pass pump configuration, short pulses with 2.8 ns duration at repetition frequencies ranging from 1 kHz to 20 kHz could be demonstrated. At 5 kHz a - to our knowledge - record pulse energy of over 500 µJ could be achieved at 755 nm in TEM00. Furthermore, a stability measurement at an energy of around 350 µJ with 5 kHz showed no degradation over 150 Mega-shots. The influence of the crystal temperature on the laser performance is also investigated, first in continuous-wave and secondly in cavity-dumped Q-switched operation.

Statistics of pulse enrgy fluctuations in a solid-state Raman laser

In this paper, we present the results of the study of the statistics of pulse energy fluctuations in a Raman laser under optical pump by the multimode nanosecond pulses. A system of coupled differential equations for slowly varying envelopes of the pump field and first three Stokes lines was integrated numerically with taking into account spatial inhomogeneity of the pump beam, spontaneous noise, and optical feedback. Data of the numerical simulation revealed a sharp increase in the fluctuation amplitude in the nonlinear regime of Raman frequency conversion when the optical length of the Raman cavity was matched with the cavity length of the multimode pump laser. At a mean 1st Stokes conversion efficiency of 3.5–3.8 %, the calculations showed an increase in the coefficient of variation (CV) of a random value from 9 % to 118 %. In the linear regime of Raman frequency conversion, when the conversion efficiency was 0.2–0.03 %, a further increase in the CV value up to 270–500 % was predicted. It is also numerically shown that the fluctuation statistics under the conditions of the cavity length matching is essentially non-Gaussian and described by the L-type probability density distributions (PDDs) with long tails and maxima located near zero. The numerical data were quantitatively confirmed by an experiment for a Raman laser on a barium nitrate crystal operated near the Raman threshold, when the 1st Stokes conversion efficiency did not exceed 0.3 %. A Raman cavity was formed by two flat mirrors providing a double-pass pump configuration. The Raman laser was excited by the linearly polarized frequency-doubled radiation of a Q-switched Nd:YAG laser generating multimode pulses with a duration of 7–8 ns. A Raman laser operating regime characterized by the hyperexponential PDDs with CVs reaching 480 %, which is 2–2.5 times higher than those observed earlier for the single-pass conditions of stimulated Raman scattering, was realized.

Efficient scheme for mid-infrared generation using simultaneous optical parametric oscillators and DFG processes in a double-pass pump configuration.

We present numerical results of an efficient scheme for mid-infrared generation using simultaneous quasi-phase matched optical parametric oscillators (OPO) and difference-frequency generation (DFG) processes in a singly resonant cavity with double-pass pump configuration. Considering an appropriately poled grating structure in MgO doped congruent lithium niobate, we have shown that it is possible to realize the double-pass pump singly resonant (DPSR) cavity configuration for the simultaneous OPO+DFG process, unlike the cascaded interaction scheme, leading to efficient mid-IR generation. Our numerical results are in agreement with the recently reported experimental results. We also present optimum parameters for the DPSR cavity configuration that could provide maximum conversion efficiency.

Compact infrared continuous-wave double-pass single-frequency doubly-resonant OPO

We demonstrate a compact continuous-wave single-frequency doubly-resonant optical parametric oscillator (DRO) in a double-pass pump configuration with a control of the relative phase between the reflected waves. The nested DRO cavity allows single longitudinal mode operation together with low threshold and high efficiency. Thermal effects are managed by chopping the pump beam, allowing continuous tuning of the emitted wavelength. The infrared idler wave (3200–3800nm) can be used for gas detection and the threshold pump power is compatible with diode pumping.

Fiber optical parametric amplifier with double-pass pump configuration

Characteristics of fiber optical parametric amplifier (FOPA) with double-pass pump configuration are experimentally investigated. The double-pass pump FOPA exhibits more than two-fold steeper gain slope in comparison to the conventional FOPA due to elongation of effective fiber length. In the L-band amplification band, a secondary idler is generated and used as the transmission signal in lieu of the original L-band signal. Gain measurement and bit error rate experiments are performed on the secondary idler and the results prove the usability of secondary idler, which is potentially useful for distribution networks.

Continuous wave tunable fiber optical parametric oscillator with double-pass pump configuration

We demonstrate a continuous wave tunable fiber optical parametric oscillator in a Fabry–Perot cavity consisting of a 500-m highly nonlinear fiber. In this work, the pump propagates in both directions together with the signal, thus making full use of its parametric gain. The resultant laser peak power is uneven across the wavelength range of interest due to wavelength-dependent phase modulation by the single-mode fiber sections in the cavity. This can be solved by filtering the idler spectral component from the oscillating cavity.

High-efficiency near-degenerate PPMgLN optical parametric oscillator with a volume Bragg grating

We demonstrate a high-efficiency near-degenerate periodically poled MgO:LiNbO(3) (PPMgLN) optical parametric oscillator (OPO) using a volume Bragg grating (VBG) output coupler (OC) pumped by a multilongitudinal Q-switched Nd:YVO(4) laser at 20 kHz repetition rate. A total parametric power of 4.3 W with a conversion efficiency of 60% is achieved in a double-pass pump configuration. The output power improvement over the case of a single-pass pump is nearly 60%. Both the signal and the idler bandwidths are less than 40 GHz and are confined within 170 GHz bandwidth at 2128.8 nm. Such efficiency is, to our knowledge, the highest ever achieved from a degenerate OPO using a VBG OC.

Spectral hole burning for ultrasound-modulated optical tomography of thick tissue

We apply spectral hole burning (SHB)-aided detection in ultrasound-modulated optical tomography (UOT) to image optical heterogeneities in thick tissue-mimicking phantom samples and chicken breast tissue. The efficiency of SHB is improved by using a Tm(3+):YAG crystal of higher doping concentration (2.0-atomic%) and a double-pass pumping configuration, in which the pump beam is transmitted through the crystal twice to burn a deeper spectral hole with the available optical intensity. With the improved SHB-UOT system, we image absorbing, scattering, and phase objects that are embedded in the middle plane of a 30-mm-thick phantom sample. The imaging resolution was 0.5 mm in the lateral direction, as defined by the focal width of the ultrasonic transducer, and 1.5 mm in the axial direction, as determined by the ultrasonic burst length. We also image two absorbing objects embedded in a 32-mm-thick chicken breast sample. The results suggest that the improved SHB-UOT system is one step closer to the practical optical imaging application in biological and clinical studies.

Optical parametric generation in 2-µm-wavelength-pumped periodically poled LiNbO_3

An optical parametric generator based on periodically poled LiNbO(3) and pumped by a 2.051-mum-wavelength laser has been demonstrated. Pump pulses of 50-ns duration of 50-Hz repetition frequency were converted into signal and idler pulses in the 3.4-5.2-mum wavelength range in a double-pass pump configuration by a 5-cm-long quasi-phase-matched crystal. An average pump power of 180 mW generated 30-mW average signal power at 3.64-mum wavelength, corresponding to 16.7% signal conversion efficiency.

Broadband tuning of a continuous-wave, doubly resonant, lithium triborate optical parametric oscillator from 791 to 1620 nm

We report the use of extreme broadband, high reflectivity >99.5%, optical parametric oscillator (OPO) cavity mirrors. A continuous-wave, doubly resonant, OPO demonstrated tuning over a range of 791-1620 nm with a single mirror set. Wavelength tuning was performed by temperature tuning the nonlinear material of lithium triborate. Narrow linewidth oscillation was confirmed throughout the tuning range, and threshold pump power increased gradually from 50 mW near the degeneracy to 800 mW at the tuning band edge in a double-pass pumping configuration.

Continuous-wave, broadband tuning from 788 to 1640 nm by a doubly resonant, MgO:LiNbO3 optical parametric oscillator

This letter reports exceptionally broadband tuning of a continuous-wave optical parametric oscillator (cw OPO) using a temperature tuned, nonlinear crystal of MgO:LiNbO3 pumped by a diode-pumped, intracavity doubled Nd:YAG laser. The tuning range from 788 to 1640 nm, is about four times broader than those ever reported in cw OPOs operating around 1 μm. This performance was accomplished by newly developed, extremely broadband, high-reflection mirrors for the doubly resonant oscillation, designed to have a reflectivity of 99% from 0.7 to 1.6 μm. Threshold pump power increased from 80 mW near degeneracy to 150 mW at the tuning band edge in a double pass pumping configuration.