1. Mid infrared laserEmission wavelength and gas absorption line coverage

ICL laser:

Covering the 3-6 μ m wavelength band, it covers the strongest absorption lines of gases such as methane (CH ₄), carbon monoxide (CO), carbon dioxide (CO ₂), and nitric oxide (NO), with absorption intensity several orders of magnitude higher than other infrared regions. For example, Nanoplus's ICL laser from Germany can provide any center wavelength of 3000nm-6000nm, making it suitable for high-sensitivity gas detection.

DFB laser:

Mainly covering the<3.5 μ m wavelength band, suitable for gas detection such as oxygen (O ₂), methane (CH ₄), carbon monoxide (CO), etc. But its threshold power density significantly increases in the frequency band above 3 μ m, which limits its performance.

QCL laser:

Covering the 4-12 μ m wavelength band, suitable for long wavelength gas detection (such as SO ₂, NO ₂), but with extremely high threshold power density within 4 μ m, power consumption and heat generation issues are prominent.

Selection suggestion:

If the absorption line of the target gas is between 3-6 μ m (such as CH ₄ CO、NO)， Priority should be given to choosing ICL lasers, whose wavelength highly matches the gas absorption line and has the best sensitivity.

If the detection gas absorption line is<3.5 μ m (such as O ₂, CH ₄), DFB laser is a low-cost choice.

If you need to cover wavelengths above 6 μ m (such as SO ₂, NO ₂), QCL laser is the only option, but you need to accept its high power consumption and cost.

2. Threshold power density and power consumption

ICL laser:

In the 3-6 μ m wavelength range, it has the lowest threshold power density. For example, Thorlabs' ID3250HHLH ICL laser has a significantly lower threshold current density than QCL at a wavelength of 3.5 μ m, with a power consumption of only 150mW (operating temperature of 20 ℃), making it suitable for portable devices.

DFB laser:

The threshold power density is low in the<3.5 μ m band, but the performance drops sharply above 3 μ m, requiring a balance between wavelength requirements and power consumption.

QCL laser:

The threshold power density is extremely high within 4 μ m, for example, QCL with a wavelength of 11 μ m requires higher input current, significant power consumption and heating issues, and requires an efficient heat dissipation system.

Selection suggestion:

ICL lasers are preferred for battery powered or portable scenarios such as vehicle exhaust telemetry and medical breath analysis, as their low power consumption can extend the device's range.

Fixed industrial monitoring systems (such as combustion exhaust gas detection) can accept high power consumption of QCL in exchange for long wavelength coverage capability.

3. Output power and detection sensitivity

ICL laser:

The typical output power is 5mW (20 ℃), which is lower than QCL. However, by selecting the strongest gas absorption line (such as CH ₄ at 3.3 μ m), ppb level detection sensitivity can be achieved. For example, ICL based quartz enhanced photoacoustic sensors have achieved ppb level concentration detection of methane and ethane.

DFB laser:

The output power is low, but with narrow linewidth and high wavelength stability, ppm level detection can be achieved in the<3.5 μ m band, which is suitable for environmental monitoring and other scenarios.

QCL laser:

The output power can reach several hundred milliwatts, supporting high concentration gas detection or long path systems, but high power may cause nonlinear effects and require optimization of optical path design.

Selection suggestion:

ICL lasers are preferred for trace gas detection, such as medical breath analysis and environmental monitoring, as their low power and high absorption line matching can achieve optimal sensitivity.

QCL lasers can be considered for high concentration gas monitoring (such as industrial process control) or long path systems (such as open path TDLAS).

4. Cost and Industrialization Maturity

ICL laser:

At present, only a few manufacturers such as Nanoplus can provide products with 3-6 μ m wavelength, which is relatively expensive (the price of a single laser is about tens of thousands of dollars). However, the European MIRPHAB project reduces size and cost through silicon-based integration technology, and is expected to achieve consumer level applications in the future.

DFB laser:

The technology is mature and the cost is low (the price of a single laser is about thousands of dollars), but the wavelength coverage range is limited, making it difficult to meet the high sensitivity detection needs of mid infrared.

QCL laser:

The cost is relatively high (the price of a single laser is about tens of thousands of dollars), and it requires efficient heat dissipation and driving circuits, further pushing up the system cost.

Selection suggestion:

Choose DFB laser for scenarios with limited budget and wavelength requirements of<3.5 μ m.

Choose ICL laser for scenarios with high sensitivity requirements and sufficient budget, such as medical and environmental protection.

Choose QCL laser for scenarios that require long wavelengths and accept high costs.

5. Comparison of typical application scenarios

Application scenarios	Recommended laser	Core strengths
Remote sensing of motor vehicle exhaust emissions	ICL	Covering the strongest absorption lines for gases such as CO and NO, with low-power support for portable devices, and real-time monitoring of exhaust emission components.
Medical Breath Analysis	ICL	Detecting trace components such as 13CO ₂ and NO in exhaled breath to diagnose diseases such as Helicobacter pylori infection and asthma, with a sensitivity of ppb level.
industrial process control	QCL	High power support for long path system, monitoring high concentration gases such as SO ₂ and NO ₂ in combustion exhaust gas, with strong anti-interference ability.
environmental monitoring	DFB/ICL	Choose DFB (such as CH ₄ and CO detection) for the<3.5 μ m band, and ICL (such as H ₂ O and HCl detection) for the 3-6 μ m band to balance cost and sensitivity.