Shanghai China

Herriott Multi-pass Absorption Cell

   The Herriott Multi-pass Absorption Cell developed by Healthy Photon independently, is applicable to a variety of common gas samples spectral analysis and test. Special lens design technologies enable the laser beam to be reflected many times inside the absorption cell, and achieve effective optical path up to decade meters in a small space in order to implement highly effective absorption of light for the small volume gas samples. Compared to White cell, Herriott cell is more stable and more resistant to light beam walk-off. It has a small size and is easy to install and operate. It is also well adapted for lab laser gas analysis, industrial process gas detection, environmental gas monitor, biochemical analysis etc.




   · Transparent gas chamber, real-time optical alignment monitoring, easy to adjust

· Two gas chambers status, free switch between open and close

· Air pressure down to decade pascal under close status, effectively reduce the overlapping interference of lines

· The laser inject port and eject port can be designed on the same side or opposite sides of the unit according to customer’s requirements

· Two structures to choose from: desk style and freestyle


Product Photo 

 multi-pass cell of 3m optical path


 multi-pass cell of 15m optical path


(Note: Healthy Photon has the ability to design optical components independently and  provide customized industrial and lab Herriott multi-pass cells according to customers requirements. The effective optical path can reach up to several meters or decade meters.) 



The cell consists of shockproof base, cell body, concave mirrors, plane mirrors, window, standard optical fiber interfaces, gas entrance and exit, heating band, temperature sensors and pressure sensors etc. Install the shockproof base inside the cell body and the gas to be measured enters the cell through the gas entrance and leaves the cell through the gas exit. The laser beam penetrates through the gas to be measured and then enters the spectral analyzer through the fiber. Compared to the original background spectrum, the absorption spectrum decreases, we can measure the gas concentration according to Lambert-Beer Absorption Law. The number of the laser beam reflections inside the cell depends on the cell length, optical path length and relevant optical design.




Effective Optical Path

14.5/3.3m (customized version available)

Beam Diameter


Gas Volume

0.84/0.05L (1 standard atmosphere)



Operation Pressure

10Pa to 102kPa

Lens Coating

Oxide layer coating metal (Reflectivity up to 98%)

Wavelength Range

0.2 to 12um

Window Material

No coating or coating CaF2/ZnSe

Main Body Material

Oxide layer protective aluminum alloy, Stainless Steel

Gas Interface

Diameter 3mm or 6mm quick connector




Upgrading Functions

√ Fixed Optical Path Fiber Collimating Input Output ----collimate the laser optical path in advance, PNP(plug and play), no need to be adjusted by users.


 √ Real-time Temperature and Pressure Sensors inside---monitor the gas temperature and pressure inside the cell in real time


√ Mid-and-Far Infrared Long Wave Optical Window---use specific materials and coating design for Mid-and-Far Infrared Band to ensure the transmittance  


Healthy Photon NH3 absorption peak around 1512nm test report

Test date2016-3-21

Required Components: TDLAS System Integrated Control Box (includes 1512nm DFB Butterfly Package Laser and its driver, phase-locked demodulated board), long path gas absorption cell (14.9m), InGaAs Detector and its operational amplifier board, NH3, and other connectors and displayers etc.


Host PC Software Parameter Setting:


 NH3 Absorption Spectrum (second harmonic)

Figure 1. High Concentration NH3

10ppmNH3 Absorption Spectrum 

ConclusionBy building and testing this NH3 system, we verified that Healthy Photon TDLAS control box and multi-pass cell both work well and have good performance. The NH3 system can detect NH3 down to 10ppm concentration very well and has low noise,  estimated sensitivity can reach up to 0.5ppmusers can feel at ease using it.


Shanghai Healthy Photon Co., Ltd. Reserved

ICP Recard: 沪ICP备14038530号

Hotline: 86 21 61111380  Welcome to: 200 East Guoding Road, Shanghai, China