mid-IR Laser Sources Research Articles

High-speed multi-THz-range mode-hop-free tunable mid-IR laser spectrometer

We report on a widely (2.25 THz or 75 cm(-1)) and rapidly (4.5 THz/s) mode-hop-free (MHF) tunable mid-IR laser source at ~3.3 μm, consisting of a 5%-MgO:LiNbO(3) singly resonant optical parametric oscillator (SRO) pumped by an automated broadly MHF tunable extended-cavity diode laser (ECDL). The broad and rapid MHF tuning capability of the ECDL is readily transferred to the SRO idler wave owing to the quasi-noncritical pump spectral acceptance bandwidth of the quasi-phase-matching. Fast and broadband high-resolution Doppler spectroscopy measurements of the ν(3) band of CH(4) are presented to illustrate the performance of the mid-IR optical parametric oscillator spectrometer.

18- \mu J energy, 160-kHz repetition rate, 250-MW peak power mid-IR OPCPA

Progresses on the development of a high repetition rate mid-IR laser source suitable for the next generation of high-field physics experiments are reported. The presented optical parametric chirped pulse amplification (OPCPA) source currently delivers carrier-envelope phase (CEP)-stable 67-fs duration optical pulses with up to 18- \mu J output energy at 160-kHz repetition rate. The focusability of the output beam (M2~2) enables peak intensities exceeding 1014 W/cm2 and the record output energy stability-below 1% power fluctuation over 4.5 h makes this source a key enabler for the strong field physics community.

On the potential of mid-IR lasers for generating high harmonics with subnanometer wavelengths in gases

The influence of the magnetic field of a laser pulse and the depletion of bound levels of working-medium atoms on the generation of high harmonics of mid-IR laser radiation in gases is investigated using numerical quantum-mechanical calculations. The maximum attainable spectral widths of high harmonics are estimated for model atoms with different ionisation potentials taking into account the aforementioned limiting effects. It is shown (within a two-dimensional model) that high harmonics with wavelengths to several angstroms can be generated by irradiating helium atoms with high-power femtosecond pulses of a laser [] with a centre wavelength of 3.9 μm. The possibility of observing experimentally relativistic effects using modern desktop mid-IR laser sources is demonstrated.

Feasibility investigation of using tunable infrared communications laser for multiwavelength digital holographic Laplacian reconstruction

Access to both the phase and intensity of an image can be provided using digital holographic (DH) imaging techniques. Recently, the difference of two holograms captured with two appropriately related wavelengths was demonstrated to produce the Laplacian of an object field. Applying telecommunication lasers the feasibility of infrared (IR) DH and DH Laplacian reconstruction and the associated theoretical analyses are presented. This is achieved by combining a tunable mid-IR laser source and mid-IR sensitive InGaAs-based digital camera.

Ionization-assisted guided-wave pulse compression to extreme peak powers and single-cycle pulse widths in the mid-infrared

Ionization-assisted spectral broadening of high-energy 10.6 μm laser pulses in a gas-filled hollow waveguide is shown to yield single-cycle pulses with multiterawatt peak powers in the mid-IR. While the highest quality of pulse compression is achieved in the regime of weak ionization, careful management of complex ionization-assisted spectral broadening of guided-wave fields is the key to compressing the output of advanced high-power mid-IR laser sources to single-cycle pulse widths.

A high power hybrid mid-IR laser source

An efficient hybrid mid-IR laser system comprising a thulium fibre laser, Ho:YAG solid state laser and a zinc germanium phosphide optical parametric oscillator is presented. A 790 nm diode pumped 1908 nm thulium fibre laser operating at 30 W pumps an RTP q-switched Ho:YAG laser emitting 17 W at 40 kHz and 2090 nm. The zinc germanium phosphide optical parametric oscillator efficiently converts this into the 3–5 μm region producing 10.1 W with 59% optical conversion efficiency and an M 2 = 1.5.

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.

Highly transparent AgGaS 2 single crystals, a compound for mid-IR laser sources, using a combined static/dynamic vacuum annealing method

Mid-IR laser sources are of great interest for many applications. One interesting way to reach such wavelengths is the frequency conversion using a nonlinear material. Thus, the crystal growth of AgGaS 2 is presented in this paper. As often reported, it must be annealed to be as transparent as possible for optical applications. Nevertheless, traditional vacuum annealings are too much long and the mechanism occurring not so well understood. Here, a new method based on a combination of a static and a dynamic vacuum annealing is proposed as well as its mechanism. Thus, highly transparent AgGaS 2 samples were obtained for further optical experiments.

High-precision CO_2 isotopologue spectrometer with a difference-frequency-generation laser source

A precision laser spectrometer for the detection of CO(2) isotopes is reported. The spectrometer measures the fundamental absorption signatures of (13)C and (12)C isotopes in CO(2) at 4.32 microm using a tunable mid-IR laser source based on difference-frequency generation. The spectrometer attains a precision of up to 0.02 per thousand for 150 s of averaging. An overall accuracy of 0.05 per thousand was obtained when sampling various calibrated reference gases.

Efficient mid-IR spectral generation via spontaneous fifth-order cascaded-Raman amplification in silica fibers

Spontaneous cascaded Raman amplification is demonstrated as a practical and efficient means of power transfer from telecommunications wavelengths to mid-IR wavelength bands through use of conventional silica fibers and amplifiers. We show that silica fibers possessing normal dispersion over all near-IR and mid-IR wavelengths can facilitate 37% and 16% efficient Raman power conversion from 1.53 microm to 2.15 and 2.41 microm wavelength bands, respectively, using nanosecond pulses from an all-fiber laser source. In contrast to supercontinuum-based techniques for long-wavelength generation, the high levels of Raman gain generated at these wavelength bands could produce useful optical amplification necessary for the development of numerous mid-IR laser sources.

Broadband difference frequency generation around 4.2 μm at overlapped phase-match conditions

Broadband difference frequency generation is theoretically and experimentally confirmed. It is shown that a wide tunable range of greater than 220 nm (FWHM) around 4.2 μm can be obtained in a 40 mm long periodically poled lithium niobate crystal with a single quasi-phase-matched period at a certain temperature. The broad bandwidth can be explained by means of the group-velocity matching or phase-mismatch minimization at overlapped phase-match conditions. The result shows that the broadband mid-infrared (mid-IR) laser source may find profound applications in trace gases detection of multiple atmospheric species and high resolution spectroscopy.

Open path atmospheric spectroscopy using room temperature operated pulsed quantum cascade laser

We report the application of a distributed feedback quantum cascade laser for 5.8 km long open path spectroscopic monitoring of ozone, water vapor and CO 2. The thermal chirp during a 140 or 200 ns long excitation pulse is used for fast wavelength scanning. The fast wavelength scanning has the advantage of the measured spectra not being affected by atmospheric turbulence, which is essential for long open path measurements. An almost linear tuning of about 0.6 and 1.2 cm −1 is achieved, respectively. Lines from the ν 3 vibrational band of the ozone spectra centered at 1031 and 1049 cm −1 is used for ozone detection by differential absorption. The lowest column densities (LCD) for ozone of the order of 0.3 ppm m retrieved from the absorption spectra for averaging times less than 20 s are better then the LCD value of 2 ppm m measured with UV DOAS systems. The intrinsic haze immunity of mid-IR laser sources is an additional important advantage of mid-IR open path spectroscopy, compared with standard UV–vis DOAS. The third major advantage of the method is the possibility to measure more inorganic and organic atmospheric species compared to the UV–vis DOAS.

Trace-gas sensor based on mid-IR difference-frequency generation in PPLN with saturated output power

The development and characterization of a compact pulsed mid-IR laser source for sensitive on-line trace-gas analyses in the 3–4 μm wavelength range is reported. The source is based on an advantageous difference-frequency mixing configuration in periodically poled LiNbO 3 (PPLN) with a cw external-cavity diode laser (ECDL; 810–830 nm) for broad and accurate tunability and a diode-pumped passively Q-switched Nd:YAG laser (1064 nm) for high mid-IR peak power. With 5 mW cw pump and 4.7 kW signal peak power incident on a 19 mm long PPLN crystal, a maximum of 360 μW mid-IR peak power was generated. The narrowband (∼150 MHz) radiation was saturated by a factor of 15 compared with the nonsaturated case due to depletion of the pump laser radiation. This results in a very high amplitude stability of the generated mid-IR power and thus in a high detection sensitivity. A minimum detectable absorption coefficient of 2.8×10 −8 cm −1 was achieved in combination with a 36.2 m multipass cell in an averaging time of 20 s, as demonstrated by on-line analyses of formaldehyde traces near 3.53 μm.

Laser photoacoustics for gas analysis and materials testing

The application of laser photoacoustics to two different areas is discussed. First, laser-induced spallation and interferometric detection of transient surface displacements is proposed as a powerful noncontact tool for the investigation of adhesion properties of solid surface coatings. Results for nickel and plasma-sprayed ceramic coatings are presented. Delamination processes at the interface between substrate and coating could be detected with excellent spatial and temporal resolution and adhesion strengths in the 0.2 to 2 GPa range be determined. Second, laser photoacoustic spectroscopy is applied to trace gas monitoring. An automated mobile CO₂ laser photoacoustic system is employed for <i>in situ</i> air monitoring with parts per billion sensitivity in industrial, urban, and rural environments. An improvement in detection selectivity for multicomponent gas mixtures is achieved with a continuously tunable highpressure CO₂ laser with a narrow linewidth of 0.017 cm^-1. A CO laser photoacoustic system previously used for the analysis of motor vehicle exhausts is now employed for studying dimerization phenomena in fatty acid vapors. Finally, emphasis is put on the development of widely tunable, narrow-band, mid-IR laser sources based on optical parametric oscillation or difference frequency generation employing tunable diode lasers and AgGaSe² as nonlinear material.