Laser systems application for urban air control Prof. V.V. Zuev - - PowerPoint PPT Presentation

Laser systems application for urban air control

• Prof. V.V. Zuev

IMCES SB RAS Tomsk

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1 2 3 4 5 6 7 8 9 10 11 12 13 λ, µ

Gas absorption bands and atmosphere transparency spectrum

sm/mol

3

Trace DIAL gas analyzer

Mobile gas analyzer version CW-CO2-laser TEA-CO2-laser

N Gas Emission lines and their combinations MDC, pрb

• n-line
• ff-line

Main bands of СО2- lasers (9 and10 mkm) emission 1 SF6 10P(16) 10P(10) 8*10-2 2 NН3 9R(30) 9R(28) 1 3 Н2О 10R(20) 10R(18) 165*10+3 4 С2Н4 10P(14) 10P(12) 2 5 О3 9P(14) 9P(22) 5 Second harmonics and total frequencies of СО2- lasers (4,5÷5,4 mkm) 6 NO 2х10P(24) 2х10P(26) 5 7 CO 2х9P(24) 2x9P(26) 4 8 OCS 2x9P(30) 2х9P(14)' 1 9 CO2 10R(30)+9R(14) 2x9P(40) 4*10+3 10 N2O 9R(40)+9R(18)2 2х9R(40) 6

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Table of analyzed gases

Major problems

• 1. Size and power-consumption minimization
• 2. Spreading of IR laser emission spectrum lines
• 3. Absorption spectra interference of various gases

Mini TEA CO2 laser and a lidar with SHG on its basis

Miniaturization

1.

Generation range spreading via sequential, hot, double hot , and sequential-hot emission bands

2.

Development of gas lasers with СО2-lasers pumping

3.

Down-conversion into the THz range with frequency tuning

Spreading of IR laser emission spectrum lines

Hot emission lines position at the wavelength up to 11,4 mkm ( dashed lines) and water absorption lines.

Generation range spreading via sequential and hot emission bands

Absorption Wavelength, mkm

At optical pumping with TEA CO2 laser that emits 0111-1110 (λ ∼11.4 µm) at the hot band the emission in the far IR spectrum range 0001-1200 (λ ∼117 µm), 0001-2000 (45.6 µm) and 2000-1110 (38.9 µm) is generated in the TEA CS2 laser.

Narrow-band tunable gas lasers with CO2-laser emission optical pumping

THz emission signals in the range of 0.5-3 THz at the capacity of a ten kV’s and detectors’ voltage output signals Down – conversion is possible in the range of 0.4≥5 THz

Tunable down-conversion of СО2 – laser emission lines in non-linear GaSe in the THz spectrum range

G FD mkm

deg

mkm

external

Abcorption, %

sm-1

Allowed spectrum of fluid in the THz spectrum range

Gas analysis selectivity growth at gases interference by means of Sub-Doppler spectroscopy

ω ω

Absorption coefficient Absorption coefficient

• ff-line on-line

1. The development of super narrow-band lasers for Sub-Doppler spectroscopy 2. СО2-laser frequency merging with microwave sources in microwave frequency waveguides ( guided/controlled spectral emission lines shift) by means of electroscopic effect

Problems

• 1. Passive frequency stabilization (a massive resonator quenches high-

frequency oscillations)

• 2. Temperature stabilization ΔТ=±1°
• 3. ТЕМ00 mode selection
• 7. Slow independent magnetostrictive adjustment of the bearing resonator rods’

length in the range of 0.1-10 mkm (quenches thermal expansion during measurements)

• 5. Piesoelectrical fixation of a single longitudinal mode to the luminescence line

center Δν Δν=2⋅10-3 sm-1

• 6. A single longitudinal mode selection via power supply choice

Super narrow-band СО2-laser

Microwave frequency waveguide cross-section with electrooptic crystal CdTe ; tunable СО2-laser and tunable magnetotron pumping.

СО2-laser frequency mixing with microwaves in microwave frequency waveguides by means of electrooptic effect

Parameters:

• The efficiency of 16 GHz – 27% frequency shift;
• Frequency tuning via mechanical waveguide nodes (sidewall shift) in the

range of 13,9-17 GHz

The advantages of the direct CO2- laser emission merging with microwave radiation:

• High sweeping frequency (~ MHz) of the emission wavelength
• Possibility to use DAS methods of the first and second derivative
• A wide range of mixed radiation detuning up to 1-1,5 sm-1 that is equivalent to

continuously tuned emission spectrum with a narrow emission line width and high energy output parameters

Gas analysis selectivity growth on long path when gases interference takes place by means of CO2- laser frequency sweeping

Summary

As a rule, urban atmospheric conditions with complex gas composite are characterized by the absorption spectra super position that hampers acquisition of selective reliable data on gas concentrations:

• One of the ways of gas analysis growth is Sub-Doppler absorption

spectra measuring in the absorption cells of low pressure (spectrophones or multi-pass cells) by means of mixed emissions of CO2-laser and microwave emissions in the microwave frequency waveguide.

• Another way is to measure on long routes with fast CO2-laser

frequency sweeping at the direct merging with the tunable microwave emission.

• Certain perspectives of laser control of atmospheric pollution are

connected with THz spectrum range analysis.

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