video corpo

Trace Gas Analysis White paper
3Pages

{{requestButtons}}

Catalog excerpts

Trace Gas Analysis White paper - 1

white paper Tunable, narrow bandwidth mid-IR laser sources for compact trace gas analysis systems with ppb sensitivity Håkan Karlsson & Sauli Sinisalo The ultimate instrumentation for trace gas analysis and detection in air quality monitoring as well as industrial process control would be one that can simultaneously provide a sensitive, selective, and fast, multi-gas measurement with wide dynamic range all in a compact and robust system. One of the few such promising technologies that can deliver these requirements is laser based photoacoustic spectroscopy (PAS). In this white paper the PAS technique is presented using the Cobolt Odin™ tunable mid-IR laser. In PAS, the rotational and vibrational states of molecules are excited with infrared light pulses and the absorbed energy translates into kinetic energy pulses, which form an acoustic wave that can be detected with a microphone (1). Due to the nature of the direct absorption detection method of the photoacoustic effect, the instrument does not require long absorption path lengths and the background drift is virtually zero. This comes from the fact, that when no target molecules are present, no signal is detected (1, 2). The photoacoustic effect was already discovered by Alexander Graham Bell in 1880, but the sensitivity of the method was quite limited by the insensitive microphone technology until the late 20th Century. Now with the current state-of-the art MEMS fabricated cantilever microphones with optical laser readout it has been possible to achieve orders of magnitude enhancement in the sensitivity and the dynamic range compared to with condenser microphones (2,3). Additionally, the silicon cantilever withstands relatively high flow rates and external stress without stretching or breaking. Lasers (QCLs), Inter-band Cascade Lasers (ICLs), DFB diode lasers and Optical Parametric Oscillators (OPOs). In many aspects the OPO technology is the most ideal choice for driving CA-PAS instruments. OPO is a non-linear optical device that down-converts the wavelength from a pump laser into two longer wavelengths in an optical resonator. Figure 2. Schematics of signal-resonant OPO based on QPM nonlinear optical crystal The emission wavelengths depend on the configuration of the nonlinear optical crystal (NLO) and the accessible wavelength span is ultimately limited only by the transmission window of the NLO. This very broad spectral selectivity and tuning capability is a general advantage of OPOs over other mid-IR light sources. More specifically OPOs can provide high output powers and freely selectable wavelengths in the 2.8-3.6 µm range which is an especially important wavelength range for sensitive hydrocarbon detection as it encompasses some of the strong-est fundamental molecular transitions of several pollutive or poisonous industrial chemicals such as BTX, C2H2, CH4, HCN, HCL, HF etc. Figure 1. Schematics of a modern cantilever enhanced photoacoustic (CE-PAS) detector Thanks to recent development in technologies for mid-IR light sources it is now possible to run cantilever enhanced (CE)-PAS instruments with monochromatic and tunable wavelengths, broad spectral selectivity and high output powers. The joint use of these technologies bring a new level in sensitivity and selectivity with below ppb (partsper-billion) sensitivity (4). There are a number of laser tech-nologies now available on the market capable of providing spectrally flexible narrow-band emission in the mid IR spectral range; Quantum Cascade This wavelength region is not readily reachable with QCL’s and the available power levels of DFBs and ICLs in this region are orders of magnitude lower than those of OPOs and not suffi-cient for extreme sensitivity. Moreover, the broad tuning capability of OPO compared to other mid-IR technologies allows for multi-gas detection of several components with common signal processing and chemometrics. The main draw-back of the OPO technology has traditionally been the bulkiness and complexity of available sources. However, recent advancements in OPO designs and laser packaging technology have enabled development of a new class of OPO devices of significantly smaller size. The Cobolt Odin™ is based on a periodically poled NLO for ultimately wavelength flexible and efficient mid-IR emission. The OPO Cobolt AB | Solna, Sweden | PHONE +46 8 545 912 30 | FA X +46 8 545 912 31 | E-MAIL info@cobolt.se | www.cobolt.se Copyright ®Cobolt AB. All rights reserved Jun

Open the catalog to page 1
Trace Gas Analysis White paper - 2

white paper white paper is pumped with a high repetition-rate 1064 nm laser and resonant for the signal wavelength resulting in up to 100 mW output power in the idler wavelength. The QPM crystal can be engi-neered for emission anywhere between 2-5 µm and tailored for narrow-band (1 nm standard, <0.2 nm custom) emission. The emission line can also be continuously tuned over >60 nm. Figure 5.The OPO based CE-PAS measurement set-up. The Cobolt Odin™ coupled into Gasera’s PA201 pho-toacoustic The numerous promising applications for the compact OPO/CE-PAS technology include for instance the...

Open the catalog to page 2
Trace Gas Analysis White paper - 3

white paper white paper In the second demonstration (6), the same OPO was used to measure benzene, toluene and 3 xylene isomers (namely, o-, p- and m-xylenes). The samples were produced by evaporat-ing anhydrous liquid samples, with known rate, into 1200 mL/min flow of nitrogen (purity 6.0) and capturing a sample into the photoacoustic cell from the sample gas flow. The measured spec-tra were analyzed with Science Based Method, as described in reference (6) resulting in multi-compound detection limits (3x rms) for benzene 4.3 ppb, toluene 7.4 ppb, p-xylene 11.0 ppb, o-xylene 6.2 ppb and...

Open the catalog to page 3

All COBOLT catalogs and technical brochures