dual-comb spectroscopy based on quantum-cascade-laser frequency combs - home battery system

Dual-
Comb spectrum in the middleinfrared—
The molecule has the strongest vibration absorption line.
Promise to provide high spectral resolution broadband spectrum at a very short acquisition time (μs)
No moving parts.
Recently, we demonstrated a quantum. cascade-laser.
We are now in a compact, double
Comb spectrometer
The noise characteristic of the ultra-poor beat is close to the limit of the beat noise. Broadband (15u2009cm−1)high-resolution (80u2009MHz)
The absorption spectra of the AAS standard apparatus and water vapor are shown, and the quantum-cascade-
Laser frequency comb as the basis for compact, all solid
Broadband chemical sensors.
QCLs is used to implement dual-
Comb spectrum Group-
The Up is not cut together, so different comb spacing is presented.
The difference between the two comb spacing is, where is the group index, for a = 6-mm-
For long devices, the maximum length difference Delta is reached between two devices less than 40 μm.
By controlling the current and/or temperature of each comb, the frequency difference delta can be set between 5 and 40 mhz.
Each comb is first made by 1-
1-inch f/1 caliber non-spherical mirror.
Our double-sample to be investigated
Comb spectrum Group-
Injecting gas batteries upward (6-Cm length with ARcoated 2-
Inch zinc selenium window).
The gas cell is also placed in the electric phase and can be moved out of the optical path.
Otherwise, low
Excellent gaasetlon is placed on the electric stage.
Both of these combs are heterogeneous into one fast (
590 mhz with a cut-off frequency of 3 db)
Thermoelectric refrigeration (TEC)
Mercury cadmium nitrateMCT)
Photovoltaic Detectors (Vigo PV-4TE-10. 6)
Give the sample signal.
Reference measurement (without sample)
, Both the sample and the LO comb were separated by the 50-50 wedge splitter and, without being affected by the studied sample, the foreign phase was separated in the second identical detector.
To avoid saturation of the detector, decay the beam with a neutral density filter.
Then, through the spectrum analyzer or 12-
Bit vertical resolution, 1 ghz analog bandwidth, 2.
5 GSample/s sampling frequency oscilloscope (
The memory of the XL memory option is 250 m samples (used for )
Or 100 MSamples per channel for L memory options (
For all other numbers)).
On the two different channels of the oscilloscope, the sampling signal and reference signal can be obtained with the same trigger. The entire set-
Up in nitrogen-
Clear the environment.
All sources of technical noise on television
A serious investigation and reduction of up.
Reduced noise and temperature fluctuations in the room by placing the complete set of equipmentup into a box.
Low Noise current driver is used for both lasers (
Wavelength electronic QCL1000)
Has a specified average current noise density.
Besides, a home
A battery system capable of driving two lasers for several hours was used.
By using a low thermal drift temperature controller, the temperature fluctuation of the laser is also reduced to less than 10 mk (
PTC10K-wavelength electronic devicesCH)with a 50-kΩ thermistor. The multi-
Detection of external signals by rapid MCT Photovoltaic Detectors (Vigo PV-4TE-10. 6).
Three narrow bandwidth (5u2009MHz)band-
Bypass filters centered on 30, 70, and mhz are used to isolate beat notes.
Three frequency counters (Agilent 53220A)
Used to calculate the frequency oscillation of the beat notes.
Active stability was implemented in order to perform weak locking (
~ 1 khz bandwidth)
For correction of multiple
Ultra-poor beat spectrum for slow drift. A band-pass filter (
Center frequency 20 mhz, bandwidth 5 mhz)
Used to isolate the fourth note used as an error signal.
The frequency oscillation of this shot is converted to amplitude oscillation by RF frequency detector (Miteq FMDM-21. 4/4-2B-
Center frequency 21.
4 MHz, 8 MHz bandwidth, 1 MHz V MHz sensitivity).
The output of the RF frequency detector is used as the input of the proportional integral correction device (
Zurich instruments HH2LI-
PID, 5 khz bandwidth)
Act on the current of one of the combs. High SNR (30u2009dB or more)
In order to be correctly detected by the frequency counter, the beat notes were used in this experiment.
Door and time control are controlled by triggers (
Agilent 33220 A, pulse mode).
In order to verify that the counter is correctly synchronized, the FM signal with a slow-changing carrier frequency (
Carrier frequency 10 mhz, frequency deviation ~ 1 khz, FM frequency ~ 1 hz)
Generated by a frequency generator (
Agilent 33220 A, FM modulation mode)
Counted by three counters
The deviation from the equal distance spacing is measured, and the value of the deviation of the equal distance spacing measured by QCL comb is shown to be at least one order of magnitude lower.
All instruments connected to the same 10-
MHz clock reference.
By blocking the two beams to evaluate the Allen deviation of the noise floor, measure the amplitude oscillation at the corresponding beat note frequency, and standardize these oscillations by the average amplitude of the corresponding beat note.
The Allen deviation of photon noise explains the amplitude oscillation of the injection, in the case that the only noise source is the shoot noise of the laser (see ).
The HITRAN 2008 database is used to simulate the transmission of water vapor in the air.
The split pressure of water vapor in the air used in the simulation is, total pressure = 101.
When the temperature is 20 °c, the temperature is 3 kPa.
The frequency resolution is set to 0. 001u2009cm.
A voitt profile is assumed and no instrument line is considered.
The transmission of water vapor is related to the voltage generated by the super differential shoot on the detector: where is the transmission ,(respectively )
Is by multiple
Ultra-poor beats with a pool of gas filled with water vapor ().
Therefore, any voltage fluctuation ()
It is characterized by s. d. ()
Affects transmission by: where is sd.
Transmission.
We assume that we estimate by measuring s. d.
And the average value of the voltage oscillation generated by each Super difference beat note, as shown.