[Instrument usage tips] How to use Mozza spectrometer

Mozza is a new spectrometer based on acousto-optic modulation for wavelength selection. The internal spectroscopic element is not the grating or prism structure in the traditional spectrometer, but a bandpass filter (Acousto-optic Tunable Filter, AOTF) based on the acousto-optic modulation of TeO2 crystal.

The center frequency of this narrowband filter is selected by controlling the frequency of the acoustic wave loaded on the crystal. Therefore, by scanning the frequency of sound waves, different frequency components of the incident beam can be selected and their optical intensity values ​​can be recorded with a detector. Finally, the acoustic frequency is reconstructed into the optical frequency to obtain the complete incident light spectrum.

Due to the advantages of Mozza's large measurement range (1-5um) and high resolution, it has increasingly become an indispensable measuring instrument in infrared spectroscopy research.

Here, we take the measurement of 3.9um, 1kHz infrared light as an example to give a summary of how to use Mozza. I hope it can provide a reference for new users who have never used Mozza and old users who have not updated the software.

Step1: Install software

Install the latest version of setup-mozza-360-r241.exe and follow the instructions and software installation wizard. I will not go into details here.

Step2: Connect the lines

Mozza's wiring is very simple, with only 3 wires in total. That is, power wire, ground wire, external trigger wire. However, there is one thing that must be noted.

If the external trigger mode is used, the repetition frequency frep needs to be ≤640kHz. Mozza only recognizes trigger signals with a level of 5V TTL, so the trigger level should be converted to 5V. The author has tried that the ~4.3V level output by Master Clock can also trigger Mozza;

Step3: Prepare light path

1. The internal spectroscopic element of Mozza is an acousto-optic crystal, which is only sensitive to S polarization. Therefore, the light to be measured must be converted to S polarization.

2. Adjust the incident light to be along a straight line on the table and level. The height is the height of the Mozza light entrance;

3. Use a reflector to guide weak energy light into the Mozza's entrance slit.

Step4: Open the instrument and software

1. Turn on the power switch on the back panel of Mozza, and you will find 3 lights on the panel. The red light on the far right is flashing, which means that the MCT photodiode is cooling down. After 30 seconds to 1 minute, the cooling will end and the red light will disappear. Please wait;

2. Open the software and check the software status, as shown in Figure 1:

Figure 1. Mozza running status

If the external trigger signal in Step 2 does not meet the requirements, the software cannot recognize the external trigger signal, and a yellow warning "NO EXTERNAL TRIGGER" will appear on the panel. If there is no warning flashing and the status bar displays the current external trigger signal, such as 1000 Hz in the picture, the external trigger signal is normal.

3. Collect spectra

A) Shine the light and click the [start] button on the software. Then Raw reference appears on the right side of the software interface, as shown in Figure

2. This signal is the signal that the incident light is directly collected by the MCT after being reflected by the beam splitter in the previous section "Basic Principles of Mozza Spectrometer". This signal reflects the intensity of the incident light. Fine-tune the orientation of the Mozza or the direction of the incident light to maximize the Raw reference signal. This means that the light to be measured correctly enters the Mozza along the designed optical path. If the warning "RAW REFERENCE SATURATION" appears, use an attenuator to reduce the intensity of the incident light. After adjusting the incident direction of light, [stop].

Figure 2. Normal operating mode

B) External trigger settings

[Advanced settings bar], select the external trigger mode [EXTERNAL], as shown in Figure 2.

Click [Operation] on the menu bar to open [Trigger Wizard], as shown in Figure 3.

Select Wavelength in [Trigger Wizard] as the center wavelength, here it is 4um;

For KHz light, the Trigger delay can be read directly by the Mozza software, that is, click the [OPT] button. In this example, the Trigger delay is automatically obtained as 959us. This function adds new functions to the new software, which greatly facilitates users and simplifies the use of the software.

At this time, the spectrum of the pulse to be measured can be accurately captured after starting the scan;

However, the Trigger delay setting is not over at this time. Please be sure to strictly follow the following steps to continue setting.

C) Accurately perform external trigger settings

In the chart of [Trigger Wizard], change the range of the left and right vertical axes until the two curves appear as shown in Figure 3(a). The blue line represents Raw reference and the orange line represents Raw Signal. Vertical red lines and red arrows represent sampling locations.

Accurately change the position of the Trigger delay so that the red line is at the maximum value of the blue line and orange line. Figure 3(a) and (b) are correct and incorrect demonstrations respectively. The wrong situation in Figure 3(b) will cause the measured spectral distortion and signal-to-noise ratio to decrease.

Note: In external trigger mode, the [OPT] function in [Trigger Wizard] is only suitable for high repetition frequency mode, that is, 1kHz≤frep≤25kHz. For low repetition frequencies, this can be selected manually.

In the external trigger mode, if the repetition frequency frep ≤ 1kHz, the trigger signal must be made 40us ahead of the light pulse to be measured; if the repetition frequency frep ≥ 1kHz, the trigger signal must arrive at the same time as the light pulse to be measured.

Figure 3. Correct (top) and incorrect (bottom) external trigger delay settings

D) Appropriately modify the scanning range [start]/[stop], scanning step [step], unit [um/cm-1/THz], average [averages] in the basic settings bar, and start scanning. This results in accurate spectra with a high signal-to-noise ratio. As shown in Figure 2.

4. When the scan is completed, save the spectrum.

Possible problems:

1. If the signal cannot be captured on the scanning panel, you can follow the following steps:

A) First, check the polarization of the beam to be measured, Mozza must use S polarization;

B) Check the position and direction of the light to be measured and whether it is parallel to the Mozza slit;

C) The wavelength of the light to be measured is not within the scanning display range;

D) Checking the trigger signal may cause the trigger signal to be out of sync with the light signal to be measured, so Mozza cannot capture the spectrum information of the light to be measured.

This process can be determined by the following method: change the Mozza operating mode to the internal trigger 1kHz mode or higher, change the scan step size to a smaller value, change the scan average to a larger value, and start scanning. If the following phenomenon occurs, as shown in Figure 4, it means that there is no problem with the above A) B) C), directly use the external trigger mode, and go to [trigger setup] to modify the "trigger delay".

2. If a yellow warning appears during use of the instrument:

A) "NO EXTERNAL TRIGGER" cannot read the external trigger signal. It may be that the trigger signal level or waveform does not meet the requirements (5V, TTL);

B) "RAW REFERENCE SATURATION", the incident light is saturated, reduce the incident light intensity or cancel the gain option on the main panel;

C) "UNCALIBRATED", the calibration file is missing or cannot be read during Mozza installation;

Figure 4. Internal trigger mode testing 1kHz signal

During the use of the instrument, you will encounter various problems. After you are familiar with the basic principles of the instrument and understand the various setting functions, these problems can basically be solved.