Difference Frequency Generation Laser Research Articles

Extending mid-infrared wavelength to 6.84 μm in oxide nonlinear optical crystal via birefringence dispersion management.

Extending lasing wavelengths to the mid-infrared (MIR) spectrum is vital for both civilian and military applications; however, it remains challenging when employing oxide nonlinear optical crystals. In this study, we report the generation of MIR nanosecond pulses via difference frequency generation (DFG) with a near-IR pump using a newly designed langasite (LGS) crystal, La3(Nb0.6Ta0.4)0.5Ga5.5O14 (LGNT0.4), which incorporates birefringence dispersion management techniques with La3Ga5.5Nb0.5O14 (LGN) as a template. Due to the improved effective nonlinear coefficients and the maintained IR cutoff relative to LGN, the tunable DFG laser in LGNT0.4 extended from 4.24 to 6.84 μm, delivering a maximum pulse energy of 16.3 μJ at 5.02 μm. To the best of our knowledge, this is the first known oxide material capable of generating tunable nanosecond pulsed lasers beyond 6 μm at μJ-level energies, demonstrating promising potential for high-intensity MIR laser systems owing to its high laser damage threshold.

Novel 40 µm spot size 3050/3200 nm DFG laser versus CO2 laser for laser-assisted drug delivery.

The use of ablative fractional lasers to enhance the delivery of topical drugs through the skin is known as laser-assisted drug delivery. Here, we compare a novel 3050/3200 nm difference frequency generation (DFG) fiber laser (spot size: 40 µm) to a commercially used CO2 laser (spot size: 120 µm). The objective is to determine whether differences in spot size and coagulation zone (CZ) thickness influence drug uptake. Fractional ablation was performed on ex-vivo human abdominal skin with the DFG (5 mJ) and CO2 (12 mJ) lasers to generate 680 µm deep lesions. To evaluate drug delivery, 30 kDa encapsulated fluorescent dye was topically applied to the skin and histologically analyzed at skin depths of 100, 140, 200, 400, and 600 µm. Additionally, transcutaneous permeation of encapsulated and 350 Da nonencapsulated dye was assessed using Franz Cells. The DFG laser generated smaller channels (diameter: 56.5 µm) with thinner CZs (thickness: 22.4 µm) than the CO2 laser (diameter: 75.9 µm, thickness: 66.8 µm). The DFG laser treated group exhibited significantly higher encapsulated dye total fluorescence intensities after 3 h compared to the CO2 laser treated group across all skin depths (p < 0.001). Permeation of nonencapsulated dye was also higher in the DFG laser treated group vs the CO2 laser treated group after 48 h (p < 0.0001), while encapsulated dye was not detected in any group. The DFG laser treated skin exhibited significantly higher total fluorescence uptake compared to the CO2 laser. Additionally, the smaller spot size and thinner CZ of the DFG laser could result in faster wound healing and reduced adverse effects while delivering similar or greater amount of topically applied drugs.

Scaling the mid-IR radiation at 7 μm - two-stage double-pass 195 MHz narrow-bandwidth DFG laser system

We present a laser system based on difference frequency generation (DFG) to produce tunable, narrow-linewidth (<30 pm), and high-energy mid-IR radiation in the 6785 nm region. The system exploits nonlinear crystals (such as LiInS2, LiInSe2 and BaGa4Se7) and nanosecond pulses generated by single-frequency Nd:YAG and Cr:forsterite lasers at 1064 and 1262 nm, respectively. Various experimental configurations are used: single-pass and double-pass through the nonlinear crystal. Additional increments of the output energy can be obtained by performing two stage double-pass geometry.

Laser-based sensing in the long-wavelength mid-infrared: chemical kinetics and environmental monitoring applications.

We present chemical kinetics and environmental monitoring applications in the long-wavelength mid-infrared (LW-MIR) region using a new diagnostic that exploits a widely tunable light source emitting in the LW-MIR. The custom-designed laser source is based on a difference-frequency generation (DFG) process in a nonlinear orientation-patterned GaAs crystal. The pump laser, an external-cavity quantum cascade laser, is tuned in a continuous-wave (cw) mode, while the signal laser, a C O 2 gas laser, is operated in a pulsed mode with a kilohertz repetition rate. The idler wavelength can be tuned between 11.58 (863.56c m -1) and 15.00µm (666.67c m -1) in a quasi-cw manner. We discuss the unique prospective applications offered by probing the LW-MIR region for chemical kinetics and environment-monitoring applications. We showcase the potential of the DFG laser source by some representative applications.

High-resolution molecular fingerprinting in the 11.6-15 µm range by a quasi-CW difference-frequency-generation laser source.

We report an approach for high-resolution spectroscopy using a widely tunable laser emitting in the molecular fingerprint region. The laser is based on difference-frequency generation (DFG) in a nonlinear orientation-patterned GaAs crystal. The signal laser, a CO2 gas laser, is operated in a kHz-pulsed mode while the pump laser, an external-cavity quantum cascade laser, is finely mode-hop-free tuned. The idler radiation covers a spectral range of ∼11.6-15 µm with a laser linewidth of ∼ 2.3 MHz. We showcase the versatility and the potential for molecular fingerprinting of the developed DFG laser source by resolving the absorption features of a mixture of several species in the long-wavelength mid-infrared. Furthermore, exploiting the wide tunability and resolution of the spectrometer, we resolve the broadband absorption spectrum of ethylene (C2H4) over ∼13-14.2 µm and quantify the self-broadening coefficients of some selected spectral lines.

A mid-IR laser diagnostic for HCN detection

Hydrogen cyanide (HCN) is a major source of prompt-NOx formation especially in fuel-bound nitrogen systems. To date, there is still a significant disagreement between experimental data and theoretical predictions of the rate coefficients of combustion reactions involving HCN as a prompt-NOx precursor. Accurate modeling of NOx formation would greatly benefit from a diagnostic capable of performing high-fidelity measurements of HCN formation/consumption time-histories. In this study, a laser diagnostic is developed for sensitive and selective HCN sensing by probing its most intense absorption feature in the mid-infrared (MIR). The diagnostic is based on difference-frequency generation (DFG) between a CO2 gas laser and an external-cavity quantum cascade laser in a nonlinear orientation-patterned gallium arsenide crystal which results in a DFG laser tunable over 11.56 − 15 µm. HCN measurements were carried out at the peak of the Q-branch of its strong ν2 vibrational band near 14 µm. Pressure dependence of the absorption cross-section was investigated at room temperature over the pressure range of 0.07 − 1.07 bar. Temperature-dependent absorption cross-section measurements were conducted behind reflected shock waves over the temperature range of 850 − 3000 K. The diagnostic was demonstrated in reactive experiments in a shock tube where HCN mole fraction time-histories were measured during the thermal decomposition of isoxazole (C3H3NO) and the first-order rate coefficients of C3H3NO → HCN + CH2CO reaction were determined.

Tunable terahertz Bessel beams with orbital angular momentum

In this work we demonstrate a frequency-tunable terahertz (THz) Bessel beam with zero- and first- order modes and orbital angular momentum, by utilizing a Tsurupica Axicon lens in combination with a picosecond difference frequency generation laser. This system enabled the selective generation of zero- or first-order THz Bessel beams with frequency-tunability across the range 3–7 THz.

Applications of TDLAS based multi-species hydrocarbon measurement using a wide scanning range DFG laser

Tunable diode laser absorption spectroscopy (TDLAS) is a widely used hydrocarbon gas sensing method in many fields. However, the short scanning range limits its application where multi-species detection is necessary. In this paper, a laser system based on TDLAS using a difference frequency generation laser was applied for the investigation of the hydrocarbon gases produced in the coal pyrolysis process and engine exhaust. The coal sample was heated up to 623 K and the recorded spectra were analyzed by the comparison with the pure hydrocarbon spectra database. A least-squares fitting was performed to quantitatively determine the concentration of each component of the mixture. Totally nine different hydrocarbons were identified and the R2 values close to 1 indicate that the variance between measured and fitted data was small. The spectra of engine exhaust were recorded and analyzed using the same method. Hydrocarbon from C3–C8 and a small amount of methane and ethene were identified. The concentration variation with time was observed.

Multi-species hydrocarbon measurement using TDLAS with a wide scanning range DFG laser

Tunable diode laser absorption spectroscopy (TDLAS) is a widely used diagnostic technique due to its high sensitivity, fast response, low cost, and other merits. Hydrocarbon detection is a field of great interest in the application of tunable diode lasers as hydrocarbons are fundamental molecules in many industrial processes. Many tunable diode lasers are only suitable for single species detection due to the short scanning range and in real situations. However, different hydrocarbon species tend to exist simultaneously. Here we present a laser system based on the difference-frequency generation (DFG) method for simultaneous hydrocarbon mixtures detection. The direct absorption spectra of different hydrocarbons covering various groups (e.g., alkane, olefin, and aromatic) were measured. The measurements of the concentration dependence of absorbance for each molecule were carried out. The R2 values were larger than 0.997, which demonstrated the system can measure hydrocarbons covering different molecular classes accurately. The mixture components were identified using the independent component analysis and quantitative analysis was performed using the classical least-squares method. Future studies will focus on the validation of the system in actual processes.

Broadband pulsed difference frequency generation laser source centered 3326 nm based on ring fiber lasers

A broadband pulsed mid-infrared difference frequency generation (DFG) laser source based on MgO-doped congruent LiNbO3 bulk is experimentally demonstrated, which employs a homemade pulsed ytterbium-doped ring fiber laser and a continuous wave erbium-doped ring fiber laser to act as seed sources. The experimental results indicate that the perfect phase match crystal temperature is about 74.5[Formula: see text]C. The maximum spectrum bandwidth of idler is about 60 nm with suitable polarization states of fundamental lights. The central wavelength of idlers varies from 3293 nm to 3333 nm over the crystal temperature ranges of 70.4–76[Formula: see text]C. A jump of central wavelength exists around crystal temperature of 72[Formula: see text]C with variation of about 30 nm. The conversion efficiency of DFG can be tuned with the crystal temperature and polarization states of fundamental lights.

一种新型的基于PPLN的多波长中红外激光光源

一种新型的基于PPLN的多波长中红外激光光源

Mid-Infrared Pulsed Laser Lithotripsy with a Tunable Laser Using Difference-Frequency Generation

A novel technique of lithotripsy was investigated with a mid-infrared tunable pulsed laser using difference-frequency generation (DFG). Human gallstone samples obtained from 24 patients were analyzed with their infrared absorption spectra. It was found that the principal components of the gallstones were different for the different patients and that the gallstone samples used in this research could be classified into four groups, i.e., mixed stones, calcium bilirubinate stones, cholesterol stones, and calcium carbonate stones. In addition, some gallstone samples had different compositions within the single stone. The mid-infrared laser tunable within a wavelength range of 5.5 - 10 μm was irradiated to the cholesterol stones at two different wavelengths of 6.83 and 6.03 μm, where the cholesterol stones had relatively strong and weak absorption peaks, respectively. As the result, the cholesterol stones were more efficiently ablated at the wavelength of 6.83 μm with the strong absorption peak. Therefore, it is suggested that the gallstones could be efficiently ablated by tuning the wavelength of the laser to the strong absorption peak of the gallstones. The higher efficiency of the ablation using the characteristic absorption peaks should lead to the safer treatment without damage to the surrounding normal tissues. In order to identify the composition of the gallstones in the patients, endoscopic and spectroscopic diagnosis using the DFG laser and an optical fiber probe made with two hollow optical fibers and a diamond attenuation total reflection prism should be useful. The absorption spectrum of the gallstones in the patients could be measured by measuring the energy of the DFG laser transmitted through the optical fiber probe and by scanning the wavelength of the DFG laser.

Spectroscopy of CH4 with a difference-frequency generation laser at 3.3 micron for atmospheric applications

The 3.25 micron spectral region is very suitable for the in situ sensing of CH4 in the troposphere and the lower stratosphere with light-weight laser sensors. Several transitions of the strong fundamental ν3 band of CH4 are revisited in this spectral region using an ultra-compact Difference-Frequency Generation (DFG) laser. Accurate intensities as well as self-broadening coefficients are reported for several manifolds that are particularly relevant to the monitoring of CH4. The study is extended to over hundred transitions reachable over the tunability range of the laser. Moreover, this DFG laser is the light source of a new, highly-compact CH4 laser spectrometer to be operated from weather balloon. The CH4 laser sensor is described and preliminary flight results are reported.

宽调谐中红外差频激光及大气水汽浓度探测

宽调谐中红外差频激光及大气水汽浓度探测

宽调谐中红外差频激光及大气水汽浓度探测

宽调谐中红外差频激光及大气水汽浓度探测

宽调谐中红外差频激光及大气水汽浓度探测

宽调谐中红外差频激光及大气水汽浓度探测

Mid-IR multiwavelength difference frequency generation based on fiber lasers

A mid-IR multiwavelength difference frequency generation (DFG) laser source with fiber laser fundamental lights is demonstrated by using the dispersion property of PPLN to broaden the quasi-phase-matching (QPM) acceptance bandwidth (BW). Our results show that the QPM BW for the pump YDFL is much larger than that for the signal EDFL. Using a multiwavelength YDFL and a single-wavelength EDFL as the pump and the signal lights, the DFG laser source can simultaneously emit 14 mid-IR wavelengths with the spacing of 14 nm at a fixed PPLN temperature. Moreover, mid-IR multiwavelength lasing lines can be synchronously tuned between 3.28 and 3.47 microm.

Mid-IR multiwavelength difference frequency generation laser source based on fiber lasers

The quasi-phase-matched (QPM) wavelength acceptation bandwidth for a difference frequency generation (DFG)mid-IR laser source with fiber lasers as the fundamental sources is effectively broadened by using the dispersion relations and its temperature characteristic of periodically poled MgO-doped LiNbO3 (PPMgLN). Our simulation results show that, with an erbium-doped fiber laser (EDFL) and a ytterbium-doped fiber laser (YDFL) respectively operating near 1550 and 1060 nm wave-bands as the signal source and pump source, for the same mid-IR wavelength regions, the allowable wavelength range given by the QPM condition for the pump wave is much larger than that for the signal wave. When the wavelength of the signal wave is fixed at 1560 nm, for a given optimized crystal temperature, the acceptance bandwidth for the pump wave is over 17 nm, corresponding to the acceptance bandwidth for the idler wave of about 180 nm. Based on it, by using a multiwavelength YDFL and a single wavelength EDFL cascaded by an erbium-doped fiber amplifier (EDFA) respectively as the pump source and the signal source, 14-wavelength mid-IR laser lines, with a spacing of about 14 nm in between, are obtained simultaneously with our QPM-DFG laser system when both the temperature and the grating period of the PPMgLN used being kept unchanged at 73.5 ℃ and 30 μm respectively. Moreover, the mid-IR multiwavelength laser lines may be tuned synchronously by varying the signal wavelength.

Difference frequency generation laser based spectrometers

AbstractTunable mid‐infrared laser sources are the key to precision optical trace gas detection. Difference‐frequency generation (DFG) based laser sources are among a few practical laser sources that have demonstrated ultra‐high detection sensitivities during real‐world applications when combined with appropriate signal enhancing and noise reduction spectroscopic techniques. This article will discuss the technical approaches, illustrate application examples of DFG sources, and offer perspectives to competing technologies.

A frequency-stabilized difference frequency generation laser spectrometer for precise line profile studies in the midinfrared

A midinfrared laser spectrometer is built up based on the difference frequency generation (DFG) of a Nd:YAG (yttrium aluminum garnet) laser and a tunable Ti:sapphire (Ti:Sa) laser. Tuning the Ti:Sa laser and operating properly with the periodically poled lithium niobate crystal, the DFG emission is tunable in the spectral range of 2.3-5.0 microm. The 1064 nm Nd:YAG laser frequency is stabilized to the 10(-6) cm(-1) level on a Doppler-broadened I(2) absorption line at 532 nm. As a result, the DFG emission frequency is stabilized within 1x10(-4) cm(-1). The measurement of an absorption line of CH(4) near 3 mum demonstrates that the DFG spectrometer is very suitable for the molecular absorption line profile studies in the midinfrared region.