Photoacoustic Detector: PA201

Research photoacoustic detector for laser sources

Custom photoacoustic gas cell for laser sources
Laser photoacoustic spectroscopy (LPAS) is a highly attractive method for the trace gas analysis dueto the high sensitivity, linearity and low sample gas volume.Tunable laser sources provide highselectivity and high measurement accuracy due to the zero background nature of the measurement
principle.
The use of the novel cantilever optical microphone provides unmatched sensitivity and enables
measurements in low pressures without compromising on the sensitivity. Narrower spectral
lines at lower pressures provide additional benefit for selectivity compared to other tunable laser
based systems operating at ambient pressure.
Gasera’s PA201 research gas cell is designed for laboratory measurements and can be tailoredfor different types of light sources such as the near infrared distributed feedback laser (DFB),
the quantum cascade laser (QCL) and the optical parametric oscillator (OPO).

Ultra-sensitive optical microphone
The heart of the system is the patented optical microphone comprising of a MEMS cantilever sensor
coupled with a laser readout interferometer that can digitally measure microscopic movements ofthe cantilever sensor, having a dynamic range greater that any analog circuitry can ever obtain.
The cantilever-type pressure sensor is designed to significantly improve the sensitivity of PAS. An
extremely thin cantilever portion moves like a flexible door due to the pressure variations in the surrounding gas. The movement of the free end of the cantilever can be about two orders of magnitude
greater than the movement of the middle point of the tightened membrane under the same pressure
variation. This is because the cantilever only bends and does not stretch.

The cantilever sensor is made out of silicon
which is a highly stabile material and thisis why the sensor is practically immune totemperature and humidity variations. Also,
the sensor is not exposed to wearing.
Pico-meter resolution of the cantilever displacement is achieved with novel opticalreadout based on laser interferometry.

The PA201 detector includes automatic gas exchange system which
can be controlled via separate controller unit.

Connections
The two gas input channels are equipped withuser changeable particle filters. The automaticgas exchange system can be programmed forgas monitoring from two different points. The
measurement enclosure can be purged with nitrogen. The photoacoustic gas cell is mounted
on a vibration-isolated support, which can belocked for transportation from the rear panel.
The laser source is connected through thefront panel. Direct fiber coupling to the photoacoustic cell is possible with a fiber connection
socket.

ExampleSpectrum of 3.7 ppm ammonia sample was measured using the PA201 combined with a continuous wave external
cavity quantum cascade laser (CW EC QCL), which was tuned over the wavenumber range from 1020 cm-1 to1100 cm-1. Mechanical chopper was used for modulation and the maximun optical power of the laser was 62 mW.

Features
Photoacoustic detector with cantilever enhanced optical
microphone
Virtual zero-background measurement principle
Total gas volume of the system is low, approx. 30 ml
The gas exchange procedure is user configurable by a simple
user interface with display and buttons. The gas exchange
can be started manually with a press of a button or theinstrument can be programmed to do it automatically usingtimer or an external trigger.
Three gas connections in the front. The sample gas has twoconnections, one for input and one for output. The input isequipped with a particle filter.
Gas cell is stabilized to 50 °C temperature.
Patented ultra-sensitive optical microphone based on aMEMS cantilever sensor coupled with a laser interferometer to measure microscopic movement of the cantileversensor.
Complies with the following standards or other standardization documents under the Low Voltage Directive
2006/95/EC and EMC Directive 2004/108/EC: EN 613261:2005, EN 61010-1: 2001.
12 months warranty

Technical specifications
Materials in contact with gas:
FPM (seals, solenoid valves)
NBR (solenoid valves, gas connectors)
PPA, PBT (solenoid valves, gas connectors)
PPS, EPDM (gas pump)
Stainless steel (solenoid valves, gas connectors)
IR-window of the cell: BaF2, KBr, ZnSe etc.
Nickel (gas exchange unit block, gas connectors)
PTFE (tubes, particle filters)
PP (particle filters)
Dimensions of the PA201 module: 17.2 cm W x 10.5 cm
H x 34.9 cm D
Weight: approx. 5 kg
Total internal gas volume: 30 ml
Operational conditions:Temperature range: 15 °C – +35 °C
Humidity range: Below 90% RH, non-condensing
Pressure range: Ambient level
Dust/water resistance: IP20 (IEC 529)
Shock/vibration endurance: Strong vibrations can affectthe measurement results.
Acoustical level: Loud sounds can affect to the measurement results

Storage conditions:Temperature range: 0 °C – +60 °C
Sample gas conditions:Temperature: Below the gas cell temperature and noncondensing
Pressure: 930 mbar – 1100 mbar
Moisture: Non-condensing at sample temperature
Gas flow with bypass flow: approx. 1 liters/minuteParticulates size < 1 μm
Gas connections:
Tube fittings for 6/4 mm tubing
Electrical connections:Power supply unit:
Input voltage: 100 - 240 Vac, 50 - 60 Hz
Input power max: 30W
Analog outputs:
Output connectors: BNC or D9 connector
Output signal voltage span: ± 3.3 V
Output signal frequency band: Low pass filtered, 0-10kHz
Output load: >2k resistive
Trigger I/O:
CMOS compatible input
Open collector output
Triggering sequence programmable
Measurement specifications:
Detection limit: Gas and light source dependent. Typicallyin the low ppb -region.
Optical path length: 100 mm at optical axis
Repeatability: < 1 % of measured value in operational
conditions at the calibration concentration (source dependent)
Temperature stability: Ambient temperature change within the operational temperature range will not cause drift.
The measurement pressure can be selected between 300
mbar - 1000 mbar.

Sales package content
PA201 photoacoustic detector
Optical microphone DSP module
Gas exchange controller module
Required cables and parts for connecting the modules
Power supply units
Measurement software for data acquisition via USB
Connector socket for optical fiber
User Manual
Storage caseGasera Ltd. reserves the right to change specifications without notice.

Gasera Ltd. | Tykistökatu 4 D, 20520 Turku, FINLAND | sales@gasera.fi | www.gasera.fi